Weissach1982

I have a recently rebuilt motor with less than 5k miles. If I wanted to switch out my regular Castrol GTX 20-W50 for some good synthetic oil, would that result in any benefits? Also, i've read that you have to flush your existing oil completely or the deposits will come loose by using synthetic oil. If anyone could help me out on this that would be great.
Cory J.
Weissach 82'

John Struthers

Cory,
As yours is a fairly recent rebuild I wouldn't worry.
Some have posted that the switch from Dino oil to synthetics like Mobile 1 result in seepage/leaks from any number of gaskets and possibly seals.
These are generally, -from post's- engines with a lot more miles/hours on them.
Reportedly, some leaks stopped all by their selves, and other reports were a simple switch back to Dino oil stopped the leaks.
Viscosity, me thinks.
I would not worry about 'deposits' breaking loose and attacking sensitive bearing surfaces or clogging anything up.
This is not like stripping paint, the filter does wonders, and again you have a low hour/mileage engine.
Unless you've been roasting your engine on a spit over a roaring fire for several days there should be little or no buildup to begin with.
I switched to Mobile 1 from -stickers- Quaker State which supposedly has an outrageous ash content.
No complaints or leaks from Pattycakes.

Weissach1982

John since you own the same car as I do, in a sense. I wanted to know about a few things.
When i'm driving around 3k rpm in any gear and speed there is a constant vibration that happens around there. Its enough to where you can feel it in the seat of the car and happens between 2800-3200rpms then goes away completely. I'm not sure what it could be, do you?
About the oil topic, you don't have to change oil in any porsche, just keep adding more because all of em will eventually leak it out. lol
Thanks John,
Cory J.

John Struthers

Cory,
If there is no clunk/thump when shifting into gear or from drive to reverse -particularly when cold- you might be looking at one of two/three things or a combo.
1. Check your half shafts for loose mount/anchor hardware.
2. Trans. mount.
3. Engine mounts. -you might have unwanted heat/sauna in cockpit with this one -.
When all else fails get under the car and really look at your tires.
Odd wear to the inside even a little or "minor" cupping (feel from sidewall to sidewall) can cause anything from a hop, buzz, hum, intermittent howl, to strange quick turn ins when turning a slow speeds or even lack of response at above normal speeds.
If you can get up on a lift or ramps check all of the above as well as any steering component boots.
I'd get into the archives on all of the above and the Nichols site as well before you jack her up.
Two other things: the minor one is resonance. Where vibration resonates at a different frequency at different engine speed -rpm-/roadspeed conditions. Make sure all your heat shields are snugged up especially if you have modified the exhaust as well as examining all hangers and the exhaust itself for rubbing or to much flex -unsupported bounce-.
Try hitting those rpms where you notice the problem now but do it in each gear. Same rpm? Make sure the Batt. is secure and there isn't anything bouncing around in the spare tire well. If you are still hauling the spare around make sure the rubber pads that keep it from vibrating on the floor are glued in place, and that the batt door/cover latches securely or ....Vibration. Get under the drivers, rear tire well- might have to pull the rear splash guard and insure the antenna is mounted securely. Mine was just hanging there it still worked but it wasn't anchored -would bounce around at certain speeds , though you'd swear it it was secure when waxing etc... .
Have you check for the dreaded thrust washer creep? Archives: TT, TC balloning. Finally how is your front spoiler? Is your belly pan still installed?

Ed MD

Still in regards to the question of benefits? In a non-turbo, non-race engine what additional benefits is a synthetic over regular like Castro other than longer times between changes. And shouldn't you change the oil filter every 5K even the oil can go 15K? I've 60K on a 85S 5 speed that has had synthetic, Mobil 1, in it since 35K after all the seals were replaced by the PO. And since then it doesn't leak oil. ( Be real, none of the Porsches that I have owned really "leaked". I have a MGB that I just rebuilt a 5 main bearing engine for racing and it still leaks, "normal sepage" per the British)
The other question has to do with the comments re: the spare. Should you run without it? I have 17" Turbo twists w/225f, 255r.
Thanks Ed Meier

mark kibort

watch out for the mobil 1. most all engine blow ups have been using this oil . Use redline 20-50 or amzoil racing 20-50. the record in the holbert car and the old 84 as well as the part euro 5 liter speaks for itself. over 100track days, no 2-6 bearing issues, and no accusump.
plus, look at the discussions with the 944 turbo guys as well. they are seeing low pressure with mobil 1, as I have seen. the oil changed out, and the pressure goes up an average of 1bar. mobil 1 looks like water when its hot!!
Just my opinion.

otherwise, change it every 3k and use Kendall 20-50.

MK



mk

heinrich

I've run Mobil1 exclusively in my S4 5-speed. It is not a racecar, but I've been through two high-G left-handers that sucked quarts of oil, and she is in perfect shape. Perfect. I bought her on dyno juice, and promptly switched to Mobil1 synth ..... she has never leaked a single drop in 35k miles and almost 3 years.

Doug Hillary

Hi,

The benefits of Synthetic v Mineral engine oils in a 928 - in normal "non race" use. This oft raised question unfortunately usually raises more questions than it answers

Firstly, the 928 engine is very easy on its engine oil. It has a large capacity sump, high oil pressure, a thermostat controlled oil cooler and a very robust and substantial oil filter.
( Some say that MANN filters are the very best made anywhere )

The 928 engine therefore starts off with a very big lubricant advantage over most others

A correct specification and viscosity synthetic oil will have the following benefits when directly compared to a similar specification mineral oil;

a) it will last longer
b) it will have better low temperature performance
c) it will have a better high temperature performance

additionally;

d) it may keep the engine's internals cleaner
e) the engine may consume less
f) the engine may run cooler ( not able to be measured via the gauge )
g) the engine may "appear" to have less rotational friction
h) see g) it may result in slightly more power

Some of the additional benefits noted above may be oil brand and type specific

There is no concrete evidence that a synthetic oil will make a car engine ( in total ) last longer if the same oil/filter change and use factors are analysed throughout the engine's life cycle. Certain internal parts ( valve train ) may have a lessor wear rate. Some circumstantial data exists but it is certainly non-conclusive

Drain intervals
The Oil Condition Reports numbered 1 to 5 on this Board show clearly that Porsche's recommended drain intervals are conservative. These intervals can be used with confidence especially when using modern oils - mineral or synthetic - that have SJ>/CF> or A3/B3 anywhere on the label

There is no conclusive evidence that more regular oil and filter changes than those recommended by the Manufacturer will extend engine life - actually it may be the reverse!

There is some University based Used Oil Analysis research data that tracks higher wear metals during the first 2-3k miles after an oil change. This may indicate that more frequent oil changes actually increase wear rates. I tend to believe this - reaserch continues

Oil Filters
The OEM oil filter ( MANN etc. ) is the only one to use in a 928. It has a high pressure by-pass valve which enables the cold oil to be filtered sooner. It is also especially constructed to take the very high cold oil pressure generated in the 928 with cold oil
Being of a large capacity it will withstand a full recommended oil change interval with ease

Brands
Well, oils ain't oils - oils are complex fluids and in real terms you get what you pay for. The more expensive oils have higher quality base fluids - both mineral and synthetic

Viscosity
The correct viscosity for your use is that nominated in your Handbook. The Porsche engineers knew best then - they still do. This is a most important part of the oils specification

For instance, subject to suitable viscosity a heavy duty "fleet" diesel oil is most suitable for the 928 and they are available as a mineral and a synthetic.
This oil should have a API CG-4>/SH> rating. Most fleet oils are sold as 15w-40 oils and are suitable for a temperature range from -15C to 40C+ ( 5F to 105F+ ) but check your Handbook
( "fleet" synthetics may have a viscosity of 5w-40 and these would be suitable for use almost anywhere - I use such an oil see Oil Condition Report No 5 on this Board )

The choice is yours !

The benefits in using a fully synthetic ATF and gear oils in the 928 are quite substantial and will definitely aid the durability of these components

Manufacturers of quality vehicles and engines have factory filled engines and the driveline with synthetic oils for many years now. The warranty and fuel efficiency benefits to them outweigh the costs

I have used synthetic lubricants for some decades and all of my fleet runs on fully synthetic lubricants

No magic oils exist but you do get what you pay for!

Regards