KFZ_schmierstoffe.pdf in German, but good reading stuff

ok guys.......what types of oils and filters are you all using?

I noticed (from a receipt of what looks like my car's last oil change) that the guy used Castrol GTX 20w50 and a WIX filter. Is it better to use a synthetic oil such as Mobile One? And will a Wix filter be ok in this car or do you all suggest something else?
Deb/'87 S4


since I started this discussion, i feel that I should end it as well.
Ok, so this might be the final version from comments I had so far:

I've been using Mobil 15w40 in my '88 928s4. Previously Castrol GTX 20w50 was used by PO. I used Mobil because think that Mobil has a very good reputation. No fancy evaluation, I know.

Viscosity (20w50) is measured in units called "weight". The "w" indicates a "winter" qualified multigrade oil. The 20 is a measure of the amount of flow at low temp, as the 50 indicates the amount at high temp. A lower rate means thicker, and more flow. It is like "less resistance to flow".
The 20w50 equals the flow of a single-weight 20 oil at low temp, and a single-50 weight when hot in a 20w50 multigrade oil. Modern oils try to stabilize the viscosity on a level 20wt~5w30, 35wt~15w50 throughout the entire temperature range (0wt-60wt). This is done by choosing a certain mixture of components.

Dino type oil:
>>Pros: cheap and decent quality available. Should however preferably not be mixed with other brands. Use a multigrade oil 15w40 or 15w50. Porsche says API/SE in older, and API/SJ spec in the newer 928. API/SJ-CF should be the minimum, which never seems to be a problem to find.
>>Cons: not the best on the market, especially in high temp fluctuation environment. It is known to leave buildup's on the seals.

Half/Semi synthetic blend:
>>Pros: fairly cheap, and better quality than Dino. Available from almost any shop, gas station etc. Can still be mixed with same Brand-dino oil whenever required (to top up). Mobil 1 is one of them. The new Mobil 1 seems to "pour" even better at low temps than a full synthetic. 20% synthetic/80% dino mix is commonly used. This ability to mix oil is one of the criteria to pass the API certification. If money is an issue, this is a fair deal. But for a few bucks more take a full-synthetic oil. Some say that the semi-synth has the same effect as a full synth. It eventually also cleans out the crud in the engine.

>>Cons: Kind a expensive for a 20/80 blend. You might mix them yourself by using the oil of same brand. At least you know what's in there.

Full synthetic oil:
>>Pros: premium performance at low and high temps, clean engine, no build up of residue because of impurities of the oil. Due to purity of synt. oil it can cope with longer intervals between oil changes. Less oil breakdown. The engine may or may not leak due to the removal of residue from previous Dino oils, and thus making room for more leaks, especially seals and gaskets. It is recommended to stay with same brand in order to avoid different additives and solvents that have negative effects on seals and o-rings. So if your seals are in top condition, you're ok. With bad seals the crud may just prevent more leakage, and cleaning out will increase the leaking. The older Mobil-1 0w15 is known to un-swell the seals causing leaks, but the engineers fixed this by altering the additive package some time ago.

>>Cons: you may reconsider using Synth. when already experiencing leaks and want to avoid the chance of more leaking. You can still switch back to Dino without big problems but this will not reverse the leaks. Try to stay within one brand to avoid other solvents working on the seals. This is one of the reasons that full. Synth gets blamed for leaks. The full Synth is the most expensive choice.

So the advice: Use a good Synthetic oil (Mobil 1 ?) when the engine seals are in good condition and money is not an issue. Always use oils from the same brand in the engine regardless of Synthetic or Dino.

See also: More Than You Ever Wanted to Know About Motor Oil

'88 928s4 cherry red
The Netherlands



Nice analysis but one thing needs correcting.

A lower API "weight" means a thinner oil that flows more easily.

Multi-viscosity oil ratings are a source of confusion because the cold rating is lower ("thinner") than the hot. Of course, oils become thicker as the temperature lowers.

The complicating factor is that back when ratings were started, oils were single-weight. The behavior for each weight was predicted for viscosity vs. temperature. When more advanced oils, "multi-weights," were developed, they didn't fit into the accepted patterns. So the two value system was adopted.

The two numbers identify what single-weight oils the multi-viscosity oil behaves like when hot and cold. So a 20w50 means like a single-weight when cold and a single-weight 50 when hot.


thanks for your comments. I meant to say the same, but reading my lines again, apparently I made a mistake. A lower rate means the resistance to flow is less, so the oil is thinner.... and you're right. Must be caused by my inability to translate the word "stroperigheid" (as we say in Dutch) into the proper English. Sorry about the confusion.

>Full synthetic oil:
>...Cons: you can no t step back to Dino oil without completely rinsing. The engine may still keep, leaking because of the cleaning of varnish the Synt. oil has done to your seals. So the engine has a tendency to leak the expensive oil a bit more due to the low viscosity.

This statement completely wrong. A full synthetics can be mixed with regular oil. That is one test that needs to be passed to get API certification. As for leaks. The reason for some motors to leak with synthetic is the fact the molecules in synthetic are all the same size and smaller. Dino oil which has all different size molecules. So worn seals might leak more with synthetics, then again maybe not. You can always switch back. Also the statement about leaks due to viscosity is also wrong. Are you telling me that a synthetic 15-50 will leak more than a conventional 5-20 just based on viscosity?

Sorry, but I needed to clear up some mis-information.

John Veninger


Like John is saying,

Leaking caused by a change to synthetic has nothing to do with the synthetic oil per se. It has to do with the relative health of the motor's seals. If the seals in the motor (o'rings, front rear main, oil pan, etc...) are old, dry and hard then the only thing making them work may be the giant wad of crud and carbon black built up behind them. Synthetic oil is a solvent for these things and it will clean them out. This can start a gusher. Going back to dino oil is not a problem and you don't need to do a flush of any kind in fact you can mix them. Ever heard of Castrol Syntec Blend? That is a mix of about 20% synth in a dino oil base. Going back to dino oil after you start a gusher may not seal your motor back up and it might. Dino oil tends to swell
seals that are old. But if the build up of crud was keeping your motor dry and you cleaned it all out on the first synth change you might not seal it back up.

Synth is good stuff and will make your engine last longer, run cooler and most important it will protect it from high temperatures where normal dino oil WILL break down! But if you have an older car (10+ years) that has a history of drips you might want to think twice before a change.

BTW, blends will also clean an engine out. Even one synth quart in 8 will start cleaning your motor out. It is dramatic. If you do a change with synth look at the first change. Black goo after a few heat cycles! Jay Kempf (not opinion I started a gusher and had to completely re-gasket my whole motor)


> >Full synthetic oil:
> >...Cons: you can not step back to Dino oil without completely rinsing.
> The engine may still keep, leaking because of the cleaning of varnish the Synt.oil has done to your seals. So the engine has a tendency to leak the expensive oil a bit more due to the low viscosity.
> This statement completely wrong. A full synthetics can be mixed with regular oil. That is one test that needs to be passed to get API certification.

I agree. Furthermore "synthetic motor oil" is not some strange wildly different elixir brought to earth by extra-terrestrials. Its exactly the same product the refinery engineer would make if only he could.

> As for leaks. The reason for some motors to leak with synthetic is the fact the molecules in synthetic are all the same size and smaller. Dino oil which has all different size molecules. So worn seals might leak more with synthetics, then again maybe not. You can always switch back.

That too is wrong. The molecules are the same size its just the synthetic engineer had more control over the mix of molecules which got into the product. Leaking gets blamed on "synthetic" when the real issue has more to do with changing the brand/blend. Once seals get soaked with one oil and its additive package, then another comes along and leaches the oil oil out of the seal, the seal un-swells, and leaks.

In ancient history when Mobil-1 was new and only available in something ridiculous such as 0W-15, it was bad about un-swelling old seals. Once this was observed the engineers fixed it by altering the additive package. But modern folklore fails to forget.

> Synth is good stuff and will make your engine last longer, run cooler and  most important it will protect it from high temperatures where normal dino oil WILL break down! But if you have an older car (10+ years) that has a history of drips you might want to think twice before a change.

I agree but think it should be emphasized that once old oil seals get used to an exact brand and blend of oil that one is asking for leaks by changing to anything else. All this hoopla about "synthetic causes leaks" is only because most often when one changes blends it just so happens to be to a synthetic.

David Kelly


Viscosity is subject to temperature. However, at the same temperature a 15W/50 or a 5W/30 can be different viscosities. It is the extreme ranges of cold and warm that vary. A multi viscosity motor oil does not change viscosity but because of synthetic additives or remanufactured Hydro-carbons (Mobil 1 has an extra molecule) It rather maintains the same viscosity through out desired temperature ranges( 0W to 60 wt.) Most manufacturers try to maintain a stabilized 20 wt for 5W/30 and approx. a 35wt for 15W/50. the newer oils now maintain a different anti wear and detergent from the oils we had. They will work but as you pointed out they sometimes do too good a job.


Wally had some interesting thoughts on synthetic oils and 928 about 6 months ago.
We want as closely an oil recommended by Porsche during the 928 lifetime.
You will not always get improved performance by going to whatever the current SAE rating is.

Example: put Mobil 1 in a Porsche 356 and you can smoke out a traffic lane better than a crop duster.
Bill Wilhoit


There has been a lot of synthetic oil discussion on the web forum.

Doug Hillary, of Airlie Beach, Australia, has done a lot of oil research.
I'll post one of his submissions. This one focuses on racing ... but an important concept discussed is High Temperature High Shear. He states Porsche's requirement is 3.5, and the older Mobil 1 didn't meet this but the newer mix may.

Another bit of research he has done is proven (for him) that synthetic oil easily meets Porsche's oil change mile recommendations - people are wasting good oil by doing changes at 3,000 miles - 5,000 miles intervals.
Once per year or 15,000 miles is quite safe.

I use Mobil 1 15W/50 in all three of my 928s. Never had leak problems, never had any oil related problems.

'93 GTS
'87 S4
''79 Euro

===Doug's June 2004 post ======


some several months ago the issue of engine oils suitable for racing was covered on here and I prepared a list - but no feed back has ever been posted

In short I had suggested:

1 - "Poor performance" by certain oils were almost certainly due to an incorrect oil choice and mis-application (The obsolete Mobil 1 TriSynthetic 0w-30 had a HTHS* vis. of about 2.6? - Porsche's HTHS minimum vis. is 3.5) Mobil 1 SuperSyn is now again at the forefront of synthetic oil technology unlike the obsolete TriSynthetic formulation

NOTE 1: "HTHS" is High Temperature High Shear and is a test of the oil's viscosity measured at 150C. It is generally accepted as the test of the oil's film strength when under load and heat. This is a very grueling test and indicates if the oil may "shear" and loose viscosity temporarily or permanently or alternatively gain viscosity through oxidation etc.
NOTE 2: Mobil's new "Mobil 1R 0w-30" specific racing oil does NOT meet Porsche's standards of viscosity of 11cSt @ 100C (10.3) and HTHS vis. of 3.5 (2.99). By all accounts it is performing very well in NASCAR vehicles and in other racing applications which may be due to its extremely advanced chemistry!

2 - Oil Brands are less important than using the correct oil specifications

3 - That oil specifications applicable and critical to "sports" use were;

a) A synthetic oil with A3/B3 ACEA specification be considered
b) The oil's viscosity should be around 5w>-40> but importantly note; c, d, below)
c) While Porsche's minimum HTHS vis. is 3.5, a HTHS vis. above 4 should be used
d) Using a HTHS vis. that was too high (5>) would sap power and perhaps hinder oil flow and cooling
e) Any oil with a HTHS vis. below 3.5 may well be a contributing cause of bearing failure in 928 engines when racing
f) After the correct HTHS vis.,oils with less than 12% evaporation during the high temperature (250C) NOACK test are probably best used in a 928 when racing

4 - That oil pressure (restriction to flow) was too often the only parameter considered rather than the combination of pressure and flow (volume)

5 - Oil flow is a constant (regardless of pressure) due to the positive displacement of the oil pump and even though pressure may be lower with certain oils at certain times, flow may be higher (oil not by passing full circulation) within the engine and therefore assist component cooling whilst still maintaining the critical film strength (HTHS above 4) needed

6 - Taking oil samples after racing use (distance/time) and conducting Used Oil Analysis (UOA) trending may provide valuable data when compared to those trends published here by me


This is the fourth and the final Oil Condition Report concerning the oil in my car - at approx. twelve (12) months and at the oil change point

The Used Oil Analysis ( UOA ) commenced nine months ago - the oil had been in the engine three months then. It was undertaken to confirm Porsche's original oil change recommendations for the 928 - namely, 20000kms or 12 months for "normal" use.

The engine oil is now at the maximum time limit set by Porsche, not the distance limit.

Used Oil Analysis is used by Equipment Manufacturers, Fleet Managers and Race Teams worldwide. The standardized testing processes compare the original ( virgin ) oil's composition alongside the used oil sample. I have been involved with this process since the late 1960's

The oil and filter were changed at this sampling point even though the Exxon Mobil report OK'd the oil for continued use

It was my call to change it out now as it follows Porsche's prescribed maximum time limit


Car - MY89 - 928S4 Auto
Speedo - 117084kms ( 72709 miles)
Oil - Shell Helix Ultra full synthetic 15w-50 - SJ/CF**, A3-96/B3-96 Oil/filter change date - 10/17/02 Distance since Oil/filter changed - 13569kms (8426 miles) Oil used since fill - nil ( level only 200ml down = total volume of all samples ) Date of this sample - 10/07/03 Distance since last sample - 2236kms (1388miles) Use in this period - 16% town,40% urban,44% hiway Avg speed in this period - 71 km/h ( 44mph) Fuel economy in this period - 11.7ltr-100km (24 mpg Imp) ( 20 mpg US ) Ambient in this period - 28c high to -2c low Ambient - annual historical averages - 27.5c max. & 21.5c min.
Ambient - actual in 12 months - max. 40c & min. -2.5c Humidity in this period - 96% highest
** This oil has a later "rating" than in the 928 S4's Handbook - technology has moved on since 1989. It is not the very latest API oil rating - SL/CF ( and A3/B3 ) - which should perform even better than this oil did over the time and/or distance limits!

Oil Condition - "use" factors;

Note - report figures below are shown thus: now-3-2-1(1=first sample)

Viscosity OK - 98-98-98-94 ( excellent ) Water OK - 0.06%-0.05%-0.01%-0.00% Soot Index OK - 0.00-0.00-0.00-0.01 TAN OK - 3.8-4.6-2.6-3.2 ( excellent ) the Max allowed is 8.9

Lab. Report Summary

Exxon Mobil's rating now - "Normal"
Status-Excellent for continued use
Last Report - "Normal"

Estimated oil's lifespan left until change required - 24500kms ( 15200 miles ) Estimated total of oil's lifespan - 38000kms ( 23500 miles )

Elemental ( & wear metal ) Analysis;

Industry "acceptable" rates (range rounded) - not 928 specific - shown as ((?))
My engine's averages are shown as [?]

Iron 10-9-7-6 ( excellent ) ((30-100)) [ 8 ] Aluminum 4-3-2-3 ( excellent ) ((5-30)) [ 3 ] Chromium 1-1-<1-1 ( excellent ) ((1-30)) [ 1 ] Copper 4-8-5-3 ( excellent ) ((10-30)) [ 5 ] Lead 7-7-4-4 ( excellent ) ((40-100)) [ 5.5 ] Silicon 5-5-11-22 ( excellent ) ((10-30)) [ 10.75 ] Sodium 6-2-2-5 ( excellent ) ((8-10)) [ 3.75 ]


None of the elemental "movements" have ever been significant. All are at or well below Industry acceptable figures. This indicates that rings, pistons, bores, cams, bearings and other major components are wearing at a very low rate

Oil Condition Summary:

The oil itself has survived for 13569kms ( nearly 8500 miles) and nearly twelve (12) months very very well. The oil's degradation has been very low and its ability to fight acidic corrosion is better than many new cheaper oils. It's viscosity has remained exceptionally close to the original new "virgin" oil - virtually no thicker or thinner than at the start 12 months ago On the oil's condition readings alone, it could have been left in for another extended period of use. This is but one advantage of a good quality synthetic lubricant

UOA Test Results Summary:

Porsche's Handbook recommendations for normal use are hereby confirmed by the UOA and with a big margin too!! Newer specification oils either mineral or synthetic, will extend the margin still further Like everything else, time has "moved on" and so has the quality of the oils we can readily purchase today. There has been about five quality upgrades since 1989 alone!!

As a result of the UOAs, the engine has now been put on to Mobil's Delvac
1 5w-40, a lighter viscosity Heavy Duty commercial diesel oil. This oil is the very latest rated diesel oil - API CI/SL - it also exceeds ACEA's A3 and B3 ( E3,4,5 & B4) and is suitable for high performance petrol engine vehicles too. It will stay on this oil as I have good access to this product - it is also used in my heavy and light trucks - and in my other cars too

It will be argued by some ( and indeed already has been here ) that my car gets an "easy life" - I accept that I am probably rated as a smooth and sensible Driver. I was involved Prototype Vehicle Development including Test Driving many years ago and by experience/knowledge do not abuse my vehicles - but I always know their limits!
I would say that my car is treated close to the way the average 928 owner treats their vehicle.

According to our "Landsharkoz" information, the ownership profile of the 928 is 95% male and aged in the 45-50 range. 57% are self employed and own two or three other cars. I'm about an "average" owner/user then, just a bit older and I own more cars! And I drive about 40000 miles per annum

I hope this is of interest



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