JET951

2017 , big year at Buchanan Automotive , we have never ever put out so much work & on the bigger jobs , the Ripple Effect is still a significant cause



Ripple Effect ? ,what ripple effect I hear you ask

Answer = Very Simple Physics with incredible damaging effects on last century Porsche engines in our climate , or just about any climate for that matter when using completely stupid Low Viscosity, Low Oil Film Strength engine oils( like the stupid use of a this century 5w-40 viscosity) in last century Porsche engines in our climate, its not as bad as it was 10-20 years ago , but its still bad enough & boy oh boy its costly to the owners & its Completely Avoidable & worst still , the use of these so called synthetic Low Viscosity , Low Oil Film Strength 5w-40 & 10W-40 engine oils has had far reaching consequences over the decades , meaning these last century Porsche engines only needed to be on a Low Oil Film strength engine oil for as little as 10,000 - 20,000 Kms to create accelerated internal engine wear & if that engine ( later ) switched back to a decent Oil Film strength 15w-50 or a 20w-50 the internal wear was slowed or even stopped( relative to how fast the wear was ) at that point in time

During 2017 we had multiple ( new to us ) 944 / 951 / 944S2 / 968 Porsche cars where we were preparing for the new owner to do a bit of club track driving & naturally with these cars typically already travelled 200,000 Kms + & some 23 to 35 years old already , we even had a very nice 968 that was low recorded Kms , but with Shocking amount of Valve Guide Wear & excessive con rod bearing wear , the silliest thing would be to take one of these old cars to the track without some basic preparation , because engine life on a race track with a human behind the steering wheel & the "Red Mist" appears ( it usually does ), engines that are worn / fatigued just go bang & its mostly avoidable & naturally ,preparation is not just the engine / engine bay ( fuel /oil /coolant hoses) , but steering & brakes + ball joints checking & or replace

Note } Red Mist is a saying when a driver gets way too excited on a track & goes all out , even though the driver had no intention at all in doing that in the first place (Male humans in cars Verses other Male humans in their cars = Interesting Mix of engines going BANG with old worn engines )

Three Main Areas of concern that we look / rectify before letting out onto the track , particularly if the previous service records show anything other that 15w-50 or 20w-50 engine oils being used previously over the decades , this applies to all 944 variants & naturally the 928 series ( two 944 engines combined ), but generally only if they are going to the track to be punished

Area of Concern 1 }

Twin Cam 944S / 944S2 / 968 ( in many ways they are basically half a 928S/32v / 928S4 / GT/GTS engine ) , yes I know there are lots of small differences , but in basic terms they a pretty much half a 928 quad cam engine & like what we see on the 928 Quad cam engines . The thin single row timing chain between the two cams , this is on the 944S , 944S2 , 968 & the quad cam 928 series , these tiny ,thin single row chains( one per head ) are quite suitable for what there are designed to do & thats simply to drive the Inlet cam by the Exhaust cam & naturally there is going to be a hydraulic ( Oil Pressure Fed) tensioner with its nylon pads putting sufficient out -ward tension on the chain , now this is where the problems start if the engine oil pressure is too low when the oil is HOT & no I am not talking about the track at the moment at all , I am talking about the years of driving , might be to & from work ( normal street deriving ) in the normal thick / heavy Sydney / Melb / Brisbane traffic snarls , engine oil hot & getting hotter ( all very normal ) except for one small detail , this poor 944 twin cam or 928 quad cam engine is on a Low Viscosity , low Oil Film Strength 5w-40 or 10w-40 so called synthetic engine oil during these few years or so , made even worst still in the simple fact that the very very low Oil Pressure at idle has to supply Oil Pressure to the timing chain tensioners at the TOP of the engine , the oil pressure that is already too low & is even lower oil pressure at the top of the engine

So what is the concern I hear you ask ?

Answer = The Death Rattle , the engine oil viscosity is so low( 5w-40 is a good contender here ) for the conditions ( mentioned above ) it means that at that normal idle speed ( in traffic ) the oil pressure at the hydraulic tensioner/s is so low the tensioner is no longer tensioning & the poor little timing chain is whipping around on and leading to the cam sprockets on the cams , this death rattle also damages the nylon tensioner guides ( shortens their lives remarkably ) and naturally beat the hell out of this thin single row chain because the engine oil is Low Viscosity & Low Oil Film Strength the metal timing chain is able to cut through the oil film( much lower oil film strength ) and bite into the cam chain "CAST" metal sprockets , causing excessive wear to them , which in turn causes more slack to occur ( metal missing from the teeth )& its a recipe for breakage & break they do and its very nasty ( bent valves , hydraulic tensioner ripped from the head & smashes through the magnesium twin cam cam-cover ( what an expensive mess )& completely avoidable

Note 1 } The" twin cam " camshafts chain sprockets are situated in the middle of the camshaft & are not replaceable separately , they are cast & machined finished with the camshaft( all one piece) , its quite a trick centre drive setup , but expensive if worn & they basically do not wear "IF" that are given every possible chance to survive , meaning good OIL PRESSURE hot at idle = 15w-50 or 20w-50 = ( correct chain tension at idle ) & sufficient Oil Film Strength Engine Oil to keep the chain from biting through the oil film & making metal to metal contact

Both Sean & I have heard the death rattle on many occasions ( engine oil hot at idle speed ) , but never when the twin cam 944s/S2/968 or quad cam 928 has been on sufficient oil viscosity for our Australian conditions = 15w-50 or 20w-50 and the basic condition of the timing chains, nylon guides & hydraulic tensioner is in reasonable to good condition

We have lost count how many " New to Us " 928 Quad Cam ( 86-95) , 944 Twin Cam ( 87-95) , 964 911 , 993 911 that had dropped by our workshop ( Mid Summer/hot day ) engine Oil Warning Pressure light Glowing RED , Oil Pressure gauge reading virtually nothing , engine making interestingly bad noises (loose timing chain noises, all at idle ) and all these were on a 5w-40 & even some 10w-40 engine oil viscosities , drained this incompatible oil out of them , changed the oil filter & refilled with 20w-50 & noises dramatically reduced or completely gone & oil pressure warning no longer glowing at idle with that oil temp , but then again is says to use 20w-50 in the owners manual that was printed by Porsche when these cars were new , so its not rocket science

On a 944S , 944 S2 or a 968 ( Twin Cam Engines ) we routinely remove the cams about every130,000 - 150,000 kms & replace the nylon tens pads ( genuine Porsche ) and the timing chain ( Street Car ) but on a more dedicated track & some road driving 944 , then we replace them more often ( cheap insurance ) , removal of the two cams on the 944 series ( 87-95) is much much easier than on a 928 quad cam , access is far better

-------------------------

Area of Concern 2 }

Valve Guide wear , like on a air /oil cooled 911 engine excessive valve guide wear is always a great concern if the said engine is taken to the track & flogged , there is a reasonable chance the engine could drop a valve head , thats because the heat from the valve head is not getting dispersed through the valve guide & into the cylinder head , instead the excessive valve guide wear is trapping the heat in the valve head just enough that at high RPM it will fail & the valve head will just fall off & into the combustion chamber ( Good Night Nurse ). Naturally the bigger the valve head the more it literally weighs & the valve springs closing force is very high & these single cam ( 2 valve heads ) are slightly more prone to it , so be careful with old Porsche engines going to the track for the first time with unknown valve guide wear ( it can catch you out easily )

As I briefly mentioned above , we had a very nice example of a 968 ( manual trans ) at our workshop recently & during repairs & tests , we had the cams out & I removed 4 or 5 of the 8 exhaust valve hydraulic lifters & I had made years ago a special tool were I can easily do a cursory valve guide wear check ( while the cams were off doing the timing chain and slipper guides ) & I was dumbfounded by the amount of( valve stem side ways movement ) valve guide wear , I even took out some of the inlet valve hydraulic lifters & even found one or two inlet valve guides with way way way too much wear ,we removed the cylinder head this 1992 968 engine ( still had its original wax fibre composite graphite head gasket )which was rotted away( good to get rid of that and install a metal custom head gasket ) , but when we had the 16 valves out , the valve guide wear was out of this world ( way way war too excessive for there Kms travelled ) long story to this car , but in a nut shell the valve guides were worn by the previous use of a low viscosity , low oil film strength engine oil , very very common 15 to 20 years ago to use these oils in these cars , but it was all the rage then ( Emperor's New Clothes ), even though the correct answer was in the owners manual printed by Porsche

Remember } There is NO Oil Pressure at the valve guides , its just very very minor splash( more of a weep at best ) & in fact the valve stem seal keeps most of it off the valve guide/valve stem , so the valve stem & valve guide relies on High Oil Film Strength engine oil ( Very Simple Physics ) , so a Low Viscosity , Low Oil Film Strength so called synthetic engine oil can easily turn into high wear for mechanical items in these engines that get No Oil Pressure

Basics Physics Time }

A this century low viscosity engine oil , say a normal street emission compliant 5w-40 ( available to the public off the shelf ) is always going to be lower oil film strength than a last century 20w-50 that has good levels of WWII vintage ZDDP AW packages & then if you compare the same 5w-40 emission compliant engine oil up against a 25w-60 racing oil( we use on track prepared 944 etc ) , then the oil film strength difference is greater still

Oil Pressure } the lower the Oil Viscosity the lower the oil pressure in the same test engine at the same oil temps , so in other words a 5w-40 will give ( Hot ) a lower oil pressure in the same last century Porsche engine than a 20w-50 engine oil ( same engine , same oil temp , same RPM Testing / reference points , Very Basic Physics )

Note 2 } In a last century 944 engine ( all ) last century 928 engine ( all ) last century 911air/oil cooled engine ( all ) , here is the list of engine components that get NO ( NO ) Oil Pressure & must rely on Oil Film Strength

A ) 944 & 928 ( all ) tall wide pointy cam lobes striking at high speed against the flat hydraulic lifter face , and the lifter/s is held up with two big valve springs ( no valve bounce with this spring tension ), this is whats known as High Wiping Loads ( High Loaded Flat Tappet Design ) , meaning the force applied is wanting to just wipe the oil clean off the lifter face , if the pointy tall cam lobe/s break through the oil film its instant metal to metal , the oil film is the liquid bearing , naturally its this area that ZDDP pressure induced cross linking AW film forms & with the correct Oil Viscosity , from minus 10 deg cel to unlimited high ambient temps = 20w-50 the cams will survive & as mentioned there is No Oil Pressure here at all , just splash

B ) 911 Air/Oil cooled , rocker shafts to cam lobes , same deal , no oil pressure , just a spray of oil in the general direction & the Oil Film Strength has to be high , same goes for the rockers pivoting on their rocker shafts , the lubrication here ZERO , oil film strength only

C ) 944 twin cam , 928 quad cam , 911 air/oil cooled Timing Chains against their Timing Chain Sprockets , , lots of forward and back shockwaves in this area ( opening and closing valves causes the shock waves ) , No Oil Pressure here to protect from excessive metal to metal contact , just slash & Oil Film Strength

D ) Alloy Pistons in their Alloy Cylinder Bores , be it 944 , 928 , 911 , No Oil Pressure here , just splash & Oil Film Strength

E ) Piston small end bearing ( top of con-rod inside piston ) , just splash feed & Oil Film Strength

F ) Piston Rings against cylinders & inside the piston lands , just splash feed & Oil Film Strength

G ) Piston gudgeon pin ( Wrist Pin in USA speak ) moves inside the alloy piston ( 944 , 928 , 911 ) and must be lubricated , no oil pressure , just a bit of splash feed & Oil Film Strength

H ) Crankshaft Thrust Bearing , this stops the crankshaft from moving forward or back in operation & with a manual transmission 944 , 928 , 911 the load from the clutch arm pushing or pulling ( depending on the design ) will transmit massive forces in one direction & if the thrust bearing is having to cope with low oil film strength engine oils there is always going to be issues with the thrust bearing

Note 3 } The crankshaft thrust bearing has grooves / openings through which the engine oil escaping from the adjacent main bearing must must be let through at the same rate as the other engine main bearings , hence the openings / grooves in the working face of the thrust bearing , in my opinion there is no oil pressure at this thrust bearing surface , and it relies on Oil Film Strength , hence why we see ZERO thrust bearing wear on any last century Porsche if its been on a 20w-50 engine oil at all times , but on lesser oil film strength engine oils we see thrust bearing wear , meaning oils like 5w-40 & some 10w-40 etc in our Australian climate , but then again the answer has always been in the owners manual that came with these last century Porsche cars

Note 4 } 928S/S4/GTS Auto Trans version / Front Flex Plate deflected & pushing the bowl shaped flywheel in constantly against the engine thrust bearing , in a nut shell we have seen many of these over the last 15 or so years that the "rear of T Tube" coupling has not been maintained & the single bolt holding it tight has stretched & with the twist of the shaft under acceleration ( shortens the shaft momentarily )& because the front coupling does not loosen as much , the shaft pulls out of the rear coupling and over time you end up with the front flex plate deflected , its not a lot of tension ( you can move the flex plate in with you thumb ) but its a constant inwards tension & with the engine thrust bearing having NO oil pressure to protect it , it has to rely on the Oil Film Strength to protect it & if the oil film strength is low , then bad luck for you , because the engine thrust bearing will wear out & the crankshaft will eventually grind through the thrust bearing & into the crankcase .
BUT we have caught quite a few ( new to us 928S / S4 / GTS 928 Auto ) cars that we have done our T Tube reset & new coupling index bolts & measure the axial play of the crank ( thrust bearing check measurement ) & the ones that are worn ( but not worn out ) we have noted / recored the wear measurement number for that particular 928 , change the engine oil & oil filter to a good quality 20w-50 & then a few years later we go back in to do a T Tube reset & re-measure the wear amount & we have never seen one yet that the wear amount has increased one bit , the wear has completely Stopped , thats because we switched back to a high oil film strength engine oil & looked after the T Tube ( very easy stuff if you know what you are doing )

Remember , the Oil Film Strength varies greatly between most 10w-40 , 5w-40 & even a few 15w-50 in different brands & even great differences between the same brand but different countries , but the difference in oil film strength between a so called synthetic this century 5w-40 engine oil( low oil film strength ) & a last century 20w-50 engine oil is remarkably different , hence why we see no 928 / S / S3 / GT / GTS thrust bearing wear at all when they have been & stay on a high oil film strength 20w-50

Area of Concern 3 }

In a 944 / 944S / 944S2 / 951 / 968 ( all ) the con-rod bearing journal ( big end bearing ) that will starve of oil pressure at high sustained RPM with normal hot oil temperature with a Low Oil Viscosity ( classic example = 5w-40 ) is journal no 2 & when it starves its all over in a second or two , crankshaft is destroyed & often the con-rod lets go = good night to the engine crankcase & sometimes cylinder head as well ( piston smashes into it , because its now free from constraint )

In a 928, 928S , 928S4 , 928GT, 928GTS ( all ) its con-rod journals no 2 & 6 ( they are on the same crank journal ) and like on a 944 its all over in a few seconds when its at high sustained RPM with the engine oil at normal high temps , the first one we came across was Charles Falzon who destroyed his engine ( on the road ) No 2 & no 6 con-rod bearings staved of oil at high RPM on a famous brand so called synthetic 5w-40 , the so called synthetic side of things did sweet F---k all for that engine ( destroyed / turned to scrap in a second or two ) & since then we have seen a few more , always on a 5w-40 or even a 10w-40

In a air / oil cooled last century 911 > 993 , they will destroy con-rod bearings 2 & 5 , not on the same journals , but in the middle of the crank , same outcome if on the wrong oil viscosity at high sustained RPM & hot operational oil temps with a 5w-40

But Why is it So ?

Answer is quite simple }

The above engines are all road engines & all road engines in last century & this century for that matter have to be functional with BOTH ends of the crankshaft to be used in practical ways , meaning the rear of the crank will need a flywheel , so there is no possible way of doing the Porsche 917 engine thing of having the engine oil pressure feed coming in at that end of the crank( axial feed ) & at the front of the engine we have on road engines pulleys, with a massive bolt in the centre holding the pulleys on that drive fan belts / A/C belts / Power Steer belts etc etc etc , so there is NO possible way of getting engine oil pressure into the front of the crank ( axial feed )

So what are we left with with all of us playing around with ROAD ENGINES , we have to put up with RADIAL feed into the crankshaft to feed oil pressure to the critical con-rod bearings ( big end bearings )


Think about it for a few seconds and it becomes crystal clear ,radial feed on road engines ( 911 , 928 , 944 ) is perfectly fine for most road conditions even at high RPM momentarily , so long as you keep the oil pressure up HIGH ENOUGH to overcome the high spinning speed of the crankshaft throwing the engine oil out ( centrifugal force ) through the very hole the oil is trying to get in to feed the Con Rod bearings along the length crankshaft , its a terrible compromise , but works OK until the Oil Pressure is insufficient & when it is at high RPM , you do not get any warning , its all over in a second or two ( BANG )

Here are some notes written by Hans Mezger ( the designer of quite a few Porsche race engines including the famous 12 cylinder 917 engine }

Because the 911 air/oil cooled engine used for road and competition had Radial feed into the crankshaft to the con-rod bearings , the Oil Pressure needed at 9,000RPM was 70 Lbs Sq " ( 5kp/cm/2) MIN pressure at max racing oil temp

The 908 ( 8 cylinder ) 3.0L air/oil cooled race engine had Radial feed to the con-rod bearings , to overcome con-rod bearing issues in racing the crankshaft required at 9,000RPM was 100 Lbs Sq " ( 7 Kp/cm/2 ) Min oil pressure at Max racing oil temp ( Thats Massive Oil Pressure )

Hence why proper race engines like the 917, 12 cylinder engine had Axial feed & with axial feed there are NO centrifugal forces pushing away the oil trying to get into the crank , so with Axial feed the 917 engine only required at 10,300 RPM was 34Lbs Sq " ( 2.3 Kp/cm/2 ) Oil pressure

So with these last century Porsche road engines we play around with , remember none of them are race engines , yes you can take them to the track , but we need to know why they go BANG & try to avoid it , so obviously we can not turn these into radial feed crank designs ( not going to happen ) , but what we can do is what Porsche did with their 1960's road / race engines , you work with what you have and recognise you need to compensate for the loss of oil pressure going to the con rod bearings ( big ends ) as the crank spins faster & faster ( radial feed has to fight against centrifugal forces ) , its not perfect but we can work with it

Using LOGIC , we know that the lower the oil viscosity , the lower the oil pressure , very simple physics & as you can see , last century Porsche road engines need high oil pressure going into the crank & thats why over the last 11 years in the PCNSW we have never lost a single 944 , 944S , 944S2 , 951 , 968 engine that compete at the track ( Supersprints ) & we and our customers have won multiple Drivers Championships & Super Sprint championships & Motorkhana Championships , so to let you into a secret we use at the track a Minium Viscosity of 25w-60 Racing oil in all these 944 variants , two of these Porsche's ( 3.0L 951's on E85 ) put out just on 600 HP and they are all wet sump , no acusump & no dry sump & remember all these Porsche's are road & track cars , meaning they all drive to the track & drive home again , they are not dedicated race cars & remember the tracks we compete at do not have some of the very very long sweeping corners that exist at some tracks in other countries , so we can get away with no dry sump in our circumstances , the closest to that is the vary fast corner 1 at Sydney Motor Sport Park , it is a very fast sweeping corner at high RPM , but we have no issues with it

So remember , prepare a last century Porsche engine for the flogging if its going to the track & the beauty of the 944 engines ( like the 928 engines) , is we can remove the engine sump to change the sump gasket & at the same time remove the individual con-rod caps to check the condition & or replace the bearing shells & cap nuts ( all in the car ) , just like on an old Datsun 1600 or Ford escort , Fantastic Design

The Above is MY OPINION in what I have experienced as a independent Porsche Specialist working on Porsche sports cars 6 days a week since 1977 ( getting on 41 years ) & the reason is I am sick & tired of seeing lovely last century Porsche engines being flogged at the track & even on the road on a way too thin this century engine oil & it all ends in tears ( Con Rod Bearings starvation mostly ) & another Porsche engine going to scrap metal ( lost forever ) , I just hope I can save a few last century Porsche engines from this stupid avoidable destruction

And lastly , the above has NOTHING at all to do with this century Porsche engines , meaning Boxster , 996 , 997 etc etc etc ,I am ONLY talking about oil viscosity & Oil Film strength & Oil pressure issues to the 944 ( all ) , 928 ( all ) and air / oil cooled 911 ( all ) road going Porsche cars from deep last century from when 20w-50 engine oils were the norm

Regards
Bruce Buchanan

FredR

Bruce,

First of all best wishes to all for the New Year and much appreciate the effort you have taken to articulate your thoughts- a fascinating read.

As you have heard from me previously and being in a climate as hot and probably more so than yours, I run a mineral oil 20W50 supplemented by a pot of STP that should make the oil a bit more viscous and hopefully to help the ZDDP content a bit. Maximum I will run this oil s 5k miles and invariably not that much.

Oil pressure is an interesting subject in its own right. At the end of the day pressure is a transport phenomena, not a lubrication performance indicator. As oil heats up its viscosity reduces and as this happens oil flow through a given restriction will increase. The trouble is the oil pump is a positive displacement device and only generates enough oil pressure to move a given amount of fluid. If there was no resistance there would be no pressure. In the case of our engines the system has a safety valve set at 8 barg so when the oil is cold the pressure goes straight to this value and then as the motor gets to operating temperature the pressure drops to circa 5 barg and pretty much maintains that from about 2500 rpm upwards give or take a bit.

Throwing a lower viscosity oil into the sump means that more oil will flow through the path of least resistance and given a fixed amount of flow this means less oil will flow elsewhere. If experience dictates a given engine needs more pressure to support lubrication what that tells me is that at lower pressures not enough oil is reaching the site of the lubrication that fails, the bearing starts to overheat and bingo it fails. Doubtless this is why the 2/6 bearing is invariably the first to fail on a 928 engine when pushed hard under certain conditions that may include lateral acceleration and direction. Oil pressure is a good general performance indicator but it does not really tell us whether oil is getting distributed as Porsche intended but if the motor is not making 5 barg then driver beware that all may not be well. When I put my S4 motor into my current 928 the local agents filled it with Mobil 1 0W40. I challenged them over this, they contacted technical support and were advised that Porsche supported this. I took the car for a soft drive, saw the oil pressure dropped to 1 barg when warmed up and promptly took it back and told them to ditch the Mobil 1 and put some Castrol GTX 20W50 in the the motor and have run on that or similar since.

That our motors have two lubrication modes often escapes peoples attention. We have force fed plain bearings and we have splash lubricated surfaces. It seems the most arduous duty is the cams and that is where the ZDDP content is critical. The ZDDP has not much to do with lubrication but it helps make the surface being splash lubricated more resilient so we need an oil that takes this need need into consideration.

On the automatics I understand you are of the opinion that this is a problem caused primarily by slippage of the rear coupling. Many of us in the rest of the world believe it is more often caused by slippage of the front coupling but the result is the same- the extended shaft puts unacceptable pressure on the thrust bearing that becomes a pseudo disc brake. An oil with lower film strength will fail first but even a 20W50 will not survive this even though it will likely survive longer.

Bottom line- our motors were designed for 20W50 oils in hot climes- seems pretty dumb to me not to use such oils as the motor was designed for. .

DeWolf

The first thing I do when I've bought home a 928 is drain the oil and fill it 20W/50 Dino oil. I change it every 5000kms. Never had an issue with pressure even driving the car in 44C.

hb253

Uh oh, new year, new oil thread.....

SwayBar

Here is a VERY interesting article on engine oils, it is very long and not for the faint-of-heart:

https://540ratblog.wordpress.com/201...-test-ranking/

To whet the appetite of those interested, here is a small snippet regarding the rampant misinformation of ZDDP:

"In addition to that, my oil test data has also been validated and backed-up by a total of FOUR other independent Industry sources. They are as follows:

1. Well known and respected Engineer and Tech Author David Vizard, whose own test data, largely based on real world engine dyno testing, has concluded that more zinc in motor oil can be damaging, more zinc does NOT provide today’s best wear protection, and that using zinc as the primary anti-wear component, is outdated technology.

2. The GM Oil Report titled, “Oil Myths from GM Techlink”, concluded that high levels of zinc are damaging and that more zinc does NOT provide more wear protection.

3. A motor oil research article written by Ed Hackett titled, “More than you ever wanted to know about Motor Oil”, concluded that more zinc does NOT provide more wear protection, it only provides longer wear protection.

4. This from the Brad Penn Oil Company:
There is such a thing as too much ZDDP. ZDDP is surface aggressive, and too much can be a detriment. ZDDP fights for the surface, blocking other additive performance. Acids generated due to excessive ZDDP contact will “tie-up” detergents thus encouraging corrosive wear. ZDDP effectiveness plateaus, more does NOT translate into more protection. Only so much is utilized. We don’t need to saturate our oil with ZDDP."


I'm glad I can help straighten that out for everyone. Carry on.

FredR

Oil companies have known for years what the optimal ZDDP content is and non that I am aware of have added more than is needed. The problem is that modern engines do not need ZDDP to the extent that engines like ours seemingly do with flat bucket tappets so the oil companies were put under environmental pressure to reduce ZDDP - they tried to find a compromise and as per info from one well known racing oil company I used to liaise with ZDDP levels ended up about half that needed for optimal protection in our older engines. More modern engines like my Cayenne turbo S allegedly do not need ZDDP and Porsche used to stuff synthetic 0W40 into these engines but were concerned about the reported rate of oil consumption [where have we heard that before] and now use oil with a higher viscosity to reduce oil consumption- so much for what the experts purport to know!

SwayBar

Not quite sure I see the correlation...

A 0w-40 and a 15w-40 has the same viscosity hot, how would that reduce oil consumption?

FredR

No idea where you got the 15w40 bit from albeit it sounds like a commonly available brew. Must check what they are currently using- I suspect it will be something like a 15w50 but I do not know that for a fact. I am a bit lazy with the Cayenne as to date I have had little trouble with it over the 5 years I have owned it. Keeping on top of the 928 is about as much as I want to attempt DIY but even that may have to change now I am a man of leisure!

JET951

Hi Fred R , happy New Year to you & you're family + all the Rennlisters as well

Regards
Bruce B

JET951

Hi SwayBar , do not think for a minute that a 0w-40 & a 15w-40 will have the same viscosity hot , it doest work that way at all in the real world , they may be close "ish" when they are both new and just poured into a test engine , but they soon get further apart more than you realise with every heat cycle as the one with more Vii's ( viscosity Index Improvers additive package begins to break down ), the wider the spectrum the more Vii's

You have to remember , we are only talking about engine oils not something strictly regulated like human baby formula made in the USA or Australia or medical , with engine oils the oil companies round up or round down numbers to something that they think the customer will recognise & buy ( its close enough ), in other words when tested, "brand X " 0w-40 may actually be closer identified as a 0w-36 & same brand 15w-40 is actually a 15w-39 or even a 15w-42 , they are just rounded off on the labelling purposes

Its gets even more interesting , one oil company will be adamant that their formulated viscosity of say a 0w-40 ( actually a 0w-37 ) is very close & is correct , then another brand but same 0w-40 labeled oil viscosity may be a 0w-35 which is slightly different again , but close enough

I have even found differences in 20w-50 oil brands & Oil Pressure ( actual) when hot

I tested on my 5.0L 928S ( 1986 quad cam ) a few years ago , very hot Sydney summers day , it was a Saturdays afternoon at work ( thats when I work on my own Porsche's ) & I wanted to change the oil on my 928S & I had a thought , the engine was stinking hot after I was in bumper to bumper traffic for an hour getting back to the workshop & my oil company Rep had previously dropped off 10 litres of 5w-50 fully synthetic engine oil ( just for me to try out ) & I was not sure at that stage whether the 5w-50 would work ( Oil Pressure Wise ) & there was no better time to do the experiment , I am reading through my old notes as I am writing this

A ) Placed my 928S on the hoist & with my engine Workshop Oil Thermometer I have ( it goes down the oil dip stick tube on a 928 to quickly measure the engine oil temp in the sump & I wrote it down ) & it was 95 deg celsius

B ) I ran the engine and took a quick note of the dash oil pressure gauge at idle in Park ( Auto Trans Park )

C ) I connected our workshop ( seperate mechanical ) Oil Pressure gauge ( only takes me 5 minutes to install ) rechecked the oil temp ( engine off ) just 95 Deg cel , ran the engine for 10 minutes to put a little heat into it & read off the actual mechanical workshop Oil Pressure gauge & like normal its nearly always a bit different to the in dash one & it read 2.2 Bar at idle in Park

D ) I drained the 20w-50 engine oil & removed the oil filter & installed a new one & then installed the 5w-50 engine oil ( same famous brand as the 20w-50 , just different viscosity )

E ) I ran the engine for quite a while , I remember even raising the coolant temp a bit by blocking off air part of the radiator to get heat into the oil as quick as possible , but being such a hot day it didn't really take that long to get the new oil in the very hot engine up to 80 deg , then 90 deg then 95 deg , at this point I read the mechanical Oil Pressure Gauge & it read = 1.9 bar at idle in Park

Oil Viscosity changes oil pressure & this taught me a valuable lesson , the last number on both these oils ( same brand ) were the same ( 50 ) , but they were similar & not the same , the 20w-50 gave better oil pressure hot & there was nothing I could do to change that

And Yes , I changed out the 5w-50 & changed the oil filter again & reinstalled new 20w-50

It was a good in the field experiment that I could do to see what happens ( on my own Porsche )

The Above is only my opinion in what I have found working on Porsche sports cars for 40 + years & nothing more

Regards
Bruce B

ptuomov

High viscosity oil makes sense to me for my car. I've got Liqui Moly 10W-60 synthetic in the blue engine. My logic for high hot viscosity is that the bearing loads are much higher with turbos.

There seems to be a tradeoff with oil flow, viscosity, and pressure. While the oil pump is a positive displacement device, the bypass circuit makes it so that for a given pressure the flow is lower with higher viscosity oil. Lower flow rate leads to somewhat poorer cooling and hotter oil in the bearings, so I've got a big *** oil cooler to go with high viscosity oil.

One potentially significant thing about the 928 oiling system is that the pickup tends to suck air in corners if the sump oil level is low. I speculate that lower flow rate of high viscosity oil leads to the sump emptying slower in cornering. It's a complex issue, so I'm just speculating.

I think that the 928 32-valve models flow more oil at low pressures and low rpms to the heads and valve train than the 944 16V models. I haven't been too concerned about the lifter and cam chain oiling for the 928s. Similarly, the bore walls seem to have too much, not too little oil.

Strosek Ultra

What is the worst oil for our 928 engines? I have used Motul 300V Competition 15W-50 oil which is supposed to be a top-end racing lubricant for racing cars. For a BMW Alpina B10 4,6L V8 it ended up as you can see from attached pictures. This particular oil has caused severe oil sludge problems in the Alpina engine not once but twice. First time I cleaned the sump and changed oil and filter. At next oil change I found the problem much worse. The oil change intervals are according to the service indicator which means about 7500 to 1000 km between oil changes. Right now I have taken the Alpina engine fully apart for cleaning. Cleaning the hydraulic valve lifters has caused me a lot of trouble but finally I managed to do it well. Most sludge has been found in the sump and at the cylinder heads. Fortunately I cannot find any abnormal wear of the engine. Normally engine oil with good cleaning additives will change color to dark brown or black after rather short useage. The Motul 300V oil retains its golden brown color even after long usage. I have two 928 cars with the same oil. It will be interesting to see how much sludge I will find when I remove the oil sump on these two engines.
Åke

SwayBar

Bruce, I appreciate you sharing your experiences. Your style reminds me of how Doug Hilary posted while he was here; I always liked his detailed posts.

I think it is safe to say, that, it's always tricky navigating an oil thread, regardless of the forum!

hb253

If you could replicate the test exactly for a variety of different brands and grades of oils, we would have more definitive information and finally have the oil thread to end all oil threads

30, 40, and 50 are grades and within each grade there is an allowable range of kinematic viscosity (measured in centistokes at 100 C). In your test, it's very possible the two oils you tested were at opposite ends of the allowable range for 50 grade. I suppose it's even possible that different batches of the same brand and grade may exhibit variation within the allowable range.

I concede that racing is a different animal, but for my street driving in the 928 and 968 (and previously 911SC) Rotella T6 5W40 works well with no discernible difference in oil pressure compared to 20W50. The 911 ran about 20 degrees cooler with 5W40 vs. 20W50.

Hugo

FredR

For purposes of consistency between manufacturers and oil blenders the SAE came up with specification J300 that quite tightly defines multi-grade viscosity requirements. To meet compliance to the SAE requirements the oil has to comply with certain defined values which can be minimum viscosity, maximum viscosity or a range of values. Thus there is no such thing as a 0W37 grade of oil albeit the intent of using the number 37 to define a range limit is understandable.

Thus not all 20w50 grades are exactly the same. Similarly multi grades with base stock viscosity of a higher number will invariably demonstrate lower oil consumption or so I have found. Back in my days of riding British motorcycles I found that a straight 40 weight oil would use less oil than a 20w50 multi grade but boy was it a pig to kick the engine over when it was cold! Castrol R is still available and popular with racers and boy does that Castor oil smell nice. Incidentally that is how "Castrol" got their name derived from "Castor Oil".