UpFixenDerPorsche

I put this up earlier in the thread.

The bottom right part of the graph opened my eyes a bit, and is why I'll be fitting an oil temp gauge.

It shows that in order to lubricate properly the oil must be hot enough for its viscosity to be the protection zone range, so it's important to have enough oil cooling available for the hot weather.

FredR

I'd be wary about putting too much credence in this diagram. Generically it has some merit but specifically it is somewhat meaningless. In lubrication the only thing that really matters is film strength versus applied load beyond that minimum drag should be the next goal as it is a parasitic loss.

I have no doubt that cold starting is a potential vulnerability but if it was terminal all motors would have pre-heaters that would not allow an engine to fire up until a certain temperature level was reached. As a rule of thumb in cold conditions I would never allow a motor to warm up at tickover and I never load an engine hard until it is up to temperature.

Our engines were designed in a different age of technology and one should be careful about what oil one uses. A 20W50 would be of concern to me were I trying to start my engine at minus 30C like Malcolm probably has to in Calgary. When I visited the place I saw many car parks had power points to connect to sump heaters. Modern low viscosity oil probably does away with such need because the oil can still flow satisfactorily at these temperatures.

In a warm climate you have the opposite problem. Porsche use Mobil 1 0w40 in the likes of my Cayenne Turbo S, even in these hot climes and the motor does not wear because it was designed for such lube. However oil consumption was such that nowadays they use a heavier grade just to modulate the oil consumption rate [a 15w50 I think] and I am happy with that. Those in the know advise that such oils are not suitable for our type of tappets- too little zinc [allegedly]. For this reason I use a mineral 20w50 with good zinc content, throw in a bottle of STP that also enhances zinc and call it quits. I then change the oil every 5k miles and possibly a bit sooner.

For track work down under it seems to make a lot of sense to run with something a little more viscous but I would not worry about cold starts down there. Start the motor and get it running at 2k to 3k rpm as soon as possible to get the oil flowing round the motor and warmed up as quickly as possible.

Over here we do not see much engine wear [providing the oil is changed regularly] and we do not have cold starts. The engine failures we do see are usually caused by failed cooling systems wherein the driver did not spot the failure in time and the heat crispy fries the oil..

Rgds

Fred

ptuomov

That temperature / zone graph is missing a loss function... how bad is it to be above or below the "zone"?

Also, it's not clear to us Rennlisters what the temperatures are referring; are they sump temperatures, temperatures of oil entering the bearing, temperatures of oil exiting the bearing, or the bearing shell itself? The doc implies it's the temperature of oil in the bearings, and that's maybe 50F or something higher than the oil in the sump. Hands up who knows the oil temperature inside the 928 bearings?

The document is oriented towards air cooled engines, which is important since many air cooled engines are really oil cooled. Does that make a difference? Furthermore, that graph's zone of protection is for the 1960 Corvair which the author says was designed to run 9.3-12.5 cSt viscosity oil in the bearings. Do we know what those values are say for the 928, which is not air/oil cooled?

I do agree with the document on a couple of things. First, one should bring the engine to operating temperature before stressing it. Second, mixing in aftermarket additives is usually a fools errand as the impact of the existing additives interacting with the new additives is impossible for almost everyone to understand.

Then again if someone has 1,000 track hours under his belt with specific "brew" and has experienced no problems, that counts for something. Whether it goes against the theory or not.

JET951

Hi John C , you can toss that chart its almost useless , actually in the case of last century Porsche engines its completely useless , the " Zone of protection" yellow line is way too funny( where did you find that ? ) , I am surprised you fell for it .As you may know , conrod ( slipper) bearing shells are protected "From" touching the crankshaft journal by oil pressure , not by an ideal temp range that is so small that no four stroke engines in the world would survive more than a day or two if that was the case , I am glad you put that up its very funny

Crankshaft conrod bearing shells ( as well as the main bearing shells ) are protected by oil pressure first & formost , in a way the oil "Pressure" contained for a moment in time is the bearing , the bearing shells & the crank journals are just the two opposite surfaces that the oil pressure is contained between ( back pressure ) as it squeezes past & back into the sump

Thats why one sees very low oil pressure at the engine oil galleries if ( indicated oil pressure) }

A ) The oil viscosity is too low as per manufacturer spec for the given ambient temp when the oil is at operating temp ( yes like a 5w-40 in a 928 in the ambient temp range you live in )

B ) The oil pressure is too low because the conrod bearings & or main bearings have too much clearance , meaning heavily worn & the oil pressure ( back pressure ) in the galleries is being lost because its getting past the bearings way too fast = hence too low oil pressure

Here is something you may find interesting as I did( about conrod bearings & oil pressure ) , I have been reading about Hans Mezger , probably Porsche's best know engine designer ( he designed the famous 917 12 cylinder racing engine , plus a stack of 911 engines & the very famous GT3 Mezger Engine ) , anyway in one of his technical papers he mentions the very interesting 8 cylinder engine Porsche used in the late 1960's , the famous 908 quad cam racing engine & the air cooled 911 racing engines

This is what he says about the oil pressure to keep the "conrod bearings " of these engines from failing

Quote } One of the criteria of a high performance engines is the lubrication quality of the connecting rod bearings , We ran comparative tests with the crankshafts which produced the following results }
The 6 cylinder 911 crankshaft needs min 5 bar ( 70lbs ) oil pressure at 9000 RPM & the 908 8 cylinder quad cam engine crankshaft requires 7 bar ( 100 Lbs ) oil pressure at the same engine speed of 9,000 RPM
End of quote .

That / those oil pressures are used to stop the conrod bearings from making contact with the journals , this is all very simple stuff

So as you can see its Oil Pressure that keeps the conrod bearings going , high oil pressure at these critical components is Extremely important & no Porsche did not race these engine on low viscosity oils for that reason

The other thing you may already know & is also very interesting is that the 928 / 944 ( all versions ) & the 911 SC & later 911 engines have a partial oil pressure gauge in their instrument cluster , meaning the oil pressure gauge only reads from 0 to 5 Bar only

The humble little 2.0L 924 & 924 Turbo & the earlier 911 series had an oil pressure gauge in the dash cluster that reads /indicates oil pressure between 0 to 10 Bar , meaning these showed complete oil pressure present

Why did I mention that ?
Answer = Because the 928 ( all versions )the Oil Pressure Relief Valve opens at about 8 bar , but we do not get to see it because the oil pressure gauge appears to be maxed out against the 5 bar stop & this gives a misleading piece of information , because the owner/driver may see only 4 bar oil pressure indicated ( engine at normal hot core temp )at high RPM , on his 928 that has an engine oil that is way too low oil viscosity for the ambient temp range , like a 5w-40, the oil pressure is too low to guarantee sufficient oil pressure at the critical no 2 & no 6 conrod journals , but on a correct 20w-50 ( as prescribed by Porsche in the owners manual ) the oil pressure will be around 2 bar higher = excellent & sufficient oil pressure where its needed ( the conrod journals)

PS , Sean posted up on youtube( bottom of this post ) today another session at last Sunday's SuperSprint at SMP , its the top video listed & titled } SMP North Porsche GT3 Playground

Here you will see stock standard Glyco ( soft) 928 / 944 conrod bearings taking punishment from a bit over 600 HP ( Sean backed off the boost because of the damp track ) & his "soft" standard Glyco conrod bearings do it easily because his engine has excellent oil pressure , and his road going ( drive to work ) 3.0L 16V E85 Porsche 951 just plays with GT3's & yes its on 25w-60 + STP ( good USA product ) & this engine never gets anything else in the way of oil , meaning Sean drives this to work summer & winter with this viscosity at all times , we actually did this as an experiment & it works fantastic for our climate

ptuomov

One clarification:

The main determinant of the required supply pressure in the galleries is the crank journal diameter for crankshafts that pick up the oil from the mains for the rods. The drilling scheme makes some difference, but the main journal diameter is the elephant in the room for cranks oiled from the mains. The oil pressure is needed to overcome the surface speed and centrifugal force of caused by the crank rotating, both going up with the square of the rpm. As long as enough oil makes it to the crank centerline, the centrifugal force will force the oil into the rods at very high pressure.

Our 928's have pretty big mains compared to most modern engines, so we need higher oil pressure than most modern engines, especially at high rpms, just for that reason alone. If the pressure is low at low rpms but the oil supplied doesn't have much air, it's usually not a problem. At high rpms, high oil pressure is absolutely necessary.

Cranks oiled from the snout can use very low supply pressures and work just fine at all rpms.

UpFixenDerPorsche

This is the source of those viscosity curves:

http://www.widman.biz/Corvair/English/Links/Oil.html

http://www.widman.biz/English/index.html


In the end I think it's up to each owner to do what they think is safest for their engine. Plenty of accounts here of pressure/viscosity loss in slow, HOT, heavy traffic situations, improved with oil cooler fans.

When I first purchased my '90 GT (using 20W-50 c/- the po) I became concerned as there was always a sense of "this feels too hot", particularly in any sort of city traffic. Further, after a brisk run up a local twisty mountain road the oil pressure was always a bar lower at idle at the top and took more revs to see 5 bar. Hmmm.

Never happened with the '89 S4 (using Delvac 5W-40). Hmmmm. Could only mean oil is getting too hot, and btw, any brand or viscosity of oil can be heated to where it's too thin to to lubricate.

As it was time for an oil change I deliberately went with a higher vis oil as a precaution until I sorted the cause of the high temps. Pentite 15W-60. Penrite says it's the same as a 15W-50 but with Extra Ten viscosity point for extreme temp running. (I still can't the rationale behind all that).

Overheating problem worsened. On 40C (104F) summer days, at 100 km/hr (60 mph), oil pressure was just below 4 bar. Turn on A/C and I could watch the needle sink below 3.5 bar. A/C off and pressure back to 3.9 bar. Increase speed to 70mph and pressure began to fall again. Then some stop/start traffic and it was under 2 bar at idle.

Then I went in search of the oil cooler. I had totally forgotten that on MY '90 cars the oil cooler had been separated form the coolant radiator. Go to the start of this thread and you'll see what I found, and why it was not helping with cooling.

OK. Clean cooler and remove the metalwork impeding airflow. Some improvement, but still unhappy in v.hot weather.

Next question: what is the 100C viscosity of this stuff? Came up with 21 cSt for the Penrite. Typical xW-50 is lower at 16 or so. Delvac 5W-40 is around 14.5. (But with a HTHS of abvout 3.2).

I reasoned that while oil flow is used to cool a bearing, a higher vis oil will take longer to pass through a bearing. If the oil is too thick, it could spend so much time inside the bearing that it will generate its own frictional heat purely because of internal shearing of the oil film, thus adding to the heat load.

OK. Went staight back to Delvac and got immediate improvements. While the viscosity still varied in hot weather, the oil pressure remained closer to 5 bar, while in slow, hot traffic it fell to abt 4.1- 4.2 bar, but overall - less pressure loss with less pressure variation. This was with a clean oil cooler, but without a fan.

Then I banged the cooler on a curb, causing a seeping leak. Grrrr.

So my friends, that is how I came to start this thread. And the thread on fixing stripped threads in the oil thermostat housing. LOL. Might get finished by this summer if I'm lucky.

JET951

Hi John , this is the GT that Laurie had/Purchased in Melbourne that I thought you purchased from Laurie ? ,the one with the 928S4 cams( wrong cams) in it because the oil film strength of the engine oil used in it ( years ago )destroyed the GT cams ? , if it is the same car , then when the previous owner had the car ( you're 1990GT ) it was on 15w-50 so called fully synthetic oil , I know because the independent Porsche specialists in Melbourne ( who serviced it for some time) only ever used 15w-50 in last century Porsche's as a lot of them do ( nothing wrong with that viscosity ), its just the oil company during the early part of this century decided to dramatically reduce the amount of ZDDP in this version of 15w-50 & hence the destroyed GT cams & the interesting part is that this same famous international oil company ( after hearing about the destruction of cams & engines on their oil ) decided some time later to reinstate the higher levels of ZDDP ( what a joke that was )

So I think you will find it has never been on a 20w-50 engine oil , at least not while it was being serviced at the independent Porsche repairer in Melbourne ( only ever 15W-50 ) & better still it was the brand you really like

UpFixenDerPorsche

Yes Bruce. That's the one.

But 18 months ago on both Rennlist and Landshark, it was the use of 5W-40 oil that you were blaming for a range of failures in both 928's and 911's, and for the failure of the cams in 'my' car.

Now, you're talking about only xW-50 oils and implying that Mobil dramatically reduced ZDDP levels in 15W-50, and that was the cause of the cam failure in 'my' car.

Bruce, as this has nothing whatsoever to do with the current thread, I have nothing more to say to you, and I do wonder what you thought you would be contributing by way of this post?

WallyP

ptuomov said, "The main determinant of the required supply pressure in the galleries is the crank journal diameter for crankshafts that pick up the oil from the mains for the rods. The drilling scheme makes some difference, but the main journal diameter is the elephant in the room for cranks oiled from the mains. The oil pressure is needed to overcome the surface speed and centrifugal force of caused by the crank rotating, both going up with the square of the rpm. As long as enough oil makes it to the crank centerline, the centrifugal force will force the oil into the rods at very high pressure."


I have a dim memory of a Porsche engineer telling about not being able to make one of the top-level racing engine's rod bearing live with approx 120 psig oil pressure and "conventional" oil feed (block to mains, into crank at mains, drilled to rod throws). When they fed from the end of the crank, both the rod and the main bearings were very happy at 18 psig...

I wonder what the NASCAR boys do to the oil flow with their 9,000 rpm V-8 engines.

Jim Devine

Might be unrelated, but someone I know runs the "F" streamliner class at Bonneville. Power is a 3 liter Ford sho engine that they run 9500 rpm. Ran a record of just over 250 with it.
They ruined a lot of parts including Moldex cranks until they opened up the rod side clearance by a lot.
Previously, the oil couldn't get out fast enough due to crank speed etc. & the bearings couldn't take it.
Might be something to it for track cars.

JET951

Hey John C , don't take my word for the early this century farce of the oil company that you really like lowering the ZDDP levels in their 15w-50 oil , ask / email Glenn Evans , he was the one that gave me the details of that oil company suddenly reinstalling the ZDDP after they realised what a problem it was causing, that's because the oil film strength on that oil with low ZDDP was very poor & hence high loaded flat tappet designed engines ( quad cam 928 series is a good last century example of this high wiping loads present ) suffered because of the low oil film strength that the oil had at that time

This emphasises the very strong combination needed in oil film strength needed in these last century Porsche engines , one might have the viscosity OK ( 15W-50 ) but that alone was not enough , the low levels of ZDDP was the clincher in this episode , in fact ( you may of seen this written as I have ) , there is info that states very low levels of ZDDP is a disaster , meaning very low levels of ZDDP works against the oil in its ability to maintain Oil Film Strength , meaning oil companies have now realised there is a PPM ( parts Per Million) ceiling that should not be lowered below in regards to ZDDP added to engine oil

Its really quite funny/sad that the paying public has to pick up the pieces ( worn out cams etc ) because oil companies experimenting for emission ACEA protocols reasons

PS } I have mentioned this episode about that particular 15W-50 with low ZDDP levels in early this century on quite a few posts before( rennlist & Landshark) , you either missed them or just didn't read them , either way no big deal , you know now

hacker-pschorr

It has been discussed and something I'm very surprised doesn't get more air time around here, the one perceived downside is you will see lower oil pressure.

The engine sitting in the corner destined for my 79 track car is only coming apart so Turbo Todd can machine the connecting rods to open up that clearance. I'm also doing the same for the 944S engine I'm putting together. Even though it's a 100% street car.

The specifications for every stroker I've seen had wider side clearances than a stock engine.

UpFixenDerPorsche

That is interesting, Hackers.

Oil can be in a bearing for just so long before it overheats and becomes part of the problem.

Oil pressure is not the be-all and end-all. Just ask your heart doctor why he gets upset when your BP is something like 220/170. Great pressure but little flow.

Rob Edwards

I essentially never see 5 bars of pressure on my stroker unless I'm way up in the rev range. Cruising around at 3K rpm, I'm typically below 4 bars.

The first road trip I called Greg shortly after I took this picture. He laughed and said, 'Yeah, they all do that'.

hacker-pschorr

IMHO it's a no-brainier to increase oil flow across the rod bearings, especially when you compare how tight the 928 tolerances are compared to other tried and proven performance engines.

A while ago I talked to Todd about adding an oil pressure sender after the rod bearings like the GM LS motors have. I think that would be very useful in a track car.