Rich9928p

A friend of mine from Germany, Dieter, owns an S4 and wrote to me about 928 oil consumption. Paraphrasing his note:

My favorite driving speed on the Autobahn is 195 kph, about 120 mph. At this speed the motor turns at 4000 rpm and I lose only a small amount, less than 0.5 liter/1000km, of oil. If I drive very fast, 250 kph or about 150 mph, and if I reach 6000 rpm often, my S4 will drink oil very hard, at a rate up to 3 - 4 liters/1000km.

This is normal when the 928 S4/GT/CS/GTS reaches 150,000 - 200,000 km but is not a problem for me because I prefer "slower" driving. I've heard about this oil consumption topic from many 928 drivers of 5.0-5.4 liter 928s.

This is what Manfred Krämer, ex-Porsche employee and owner of Krämer Motorsport-Service, told me about this problem:

1. The oil sump is much too small for this large of an engine because there is not enough space in the engine compartment. The oil doesn´t have enough time to reach fluid state and is often in a gasious state.

2. The silicon crystals in the cylinder bores are responsible for sealing, too. After 150,000 -200,000 km the bores become polished and you lose oil which is in the gasious state due to air-pressure within the engine.

Manfred Krämer knows a method to repair cylinders which is less expensive than reboring.

Doug Hillary

Hi Rich,
This may help a little - it may not

The Porsche 928 has a very simple engine oil specification, it was not even demanding in the late series engines ( except perhaps for the GTS ). They specified a SE/CC or SF/CD. It is noted though that the diesel specs. CC and CD were mentioned - this was probably to combat the effects of soot/carbon buildup ?

1 -This then tends to suggest that the Porsche Engineers knew that under "all anticipated operating conditions" there was enough "technical" capacity in their engine and recommendations in their Drivers' Handbook. Of course it did, warranty liabilities would have dictated this and changes if needed would have been swift

2 - The lubrication system's capacity has not been significantly changed over the years of production. Even in 1992 the 928 range was on synthetic SF-CC/CD or SG-CC/CD as a factory fill. This tends to suggest that there were no major warranty issues stemming from this area. A controlled oil temperature via thermostats and an oil cooler was as far as they felt they needed to go

Personally I think that the oil in S4 engines will get "very hot" - <120C> - under certain operating conditions, especially high speed/high load work in tailwinds and high ambient temperatures

Oils are rated at a High Temperature/High Shear Stability point of 150C. Synthetic oils usually perform substantially better at high temperatures - and in most engine local hot spots sent the oil to very high temperatures for short periods. Mr Kramer gives no details of the oil he uses

The "gaseous" state mentioned in Mr Kramer's comments may well occur although I doubt it as a typical "flash point" for a modern mineral oil ( not perhaps 0/5W10w-30 ) is 200C+, with synthetics usually 230C+

As far as Mr Kramers comments that the oil "...not having enough time to return to a fluid state and is often in a gaseous state..." -he would have surely picked this up as a lack of oil pressure......!!!!?????

What does occur in the crankcase is that large volumns of oil "mist" is created by the many reciprocating/turning components and this is handled by the crankcase ventilation system
This may lead in certain conditions to higher than normal oil consumption at high revs. 928 engine builders would be able to answer this!

3 - Porsche like most German manufacturers at least, publish an "oil consumption" rate. In the S4 engine this is at 1.5 litres per 1000 kms ( Isn't this about a quart in 500 miles ? ). This is the limit before they would ever have looked at an oil consumption issue under warranty and would be related to a "normal use" ( normal fuel consumption ) cycle - and not always at "...6000 rpm often..."!
Most engine makers use an even better method to measure "absolute" oil consumption - based on engine use. This method relates oil use to "absolute" fuel consumption. This the best, most accurate way to measure oil consumption as it is related to the way the engine has been used ( how "hard" or "easy" ) in real terms!

Using the correct oil viscosity - as recommended - is always very important and it is likely that the lower viscosity mineral oils may be consumed at a higher rate than the heavier oils, or the synthetics recommended

Many Drivers expect zero oil consumption. Using small amounts of oil within certain limits - in any engine - is beneficial

4 - Topping up the oil provides a technical benefit too. By adding oil to/near the upper dipstick mark you are restoring some of the oil's "additive package" - a good thing

5 - I am not capable of commenting on Mr Kramer's other comments about "silicon crystals"

I can recollect a Porsche Service Bulletin of 1986 concerning the finishing of the cylinder bores to ensure "...that the silicon particles protrude from the aluminium so that the pistons and rings make contact with the silicon..." This MAY suggest that running on the aluminium as a finish did lead to sealing problems

Any engine that has covered 150000-200000 kms will usually be worn somewhat from its original clearances. Previous use cycles, care, type of lubricants and the amount of wear on related components will normally dictate oil consumption

I hope this "ramble on" contributes something - even just to debate!

Regards

Erik - Denmark

Rich wrote:
Manfred Krämer knows a method to repair cylinders which is less expensive than reboring.
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Hello Rich,
Do you know more about this method?

Rich and Doug
Interesting discussion matter

Doug wrote:
What does occur in the crankcase is that large volumns of oil "mist" is created by the many reciprocating/turning components and this is handled by the crankcase ventilation system
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I damaged a brand new block during a long and fast drive (5500-6000 RPM) from Denmark to Le Mans in France -
This was due to detonation and most properly due to 'mist' oil/crank vent system.
This happens in my old car, 1980 Euro 3 aut., this car is relatively low geared, now I changed to 1984 Euro 4 aut this car is app. 16% heigher geared - I.e. lower RPM at top speed.
Also I installed one more oil separator (Cyclone) for preventing oil mist to reach to the combustion chambers
I wish I had a knocking regulation (or at least warning) system
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Rich9928p

Perhaps my use of the word gaseous was incorrect in my paraphrasing. Foam or mist might have been better, i.e. the oil is still liquid but is suspended within the swirling air within the engine.

BTW, Mist has a much different meaning in the German lanugage. It means dung or manure. So be careful with your vocabulary!

Rich

Fastest928

There are four possibilites for loss of oil in an engine:

1 past the rings
2 past the valve seals
3 through recycle of crankcase vapor
4 gasket based leaks

In a new engine, it is unlikely that items 1, 2, 4 will occur if the engine is operating at the middle of its operating range

As the engine ages, 1, 2 and 4 become the primary oil loss factors

As the engine runs hotter, 1 becomes very large factor as tol's open up beyond spec. Remember, the piston to wall clearance at room temp is .0008" for a new engine. Mahle/goetze specs are very precise for this operation, which makes boring the blocks properly a real bitch!

It is pure rumor that the 928 cylinder wall do not wear...they just wear much less than cast iron..and they do wear the pistons and rings.

Early 928s have an oil pumping issue at high rpms...another topic

I am very interested in any method to improve the ring seal between the rings and bore that does not require engine disassembly!

Regards
Marc

Old & New

marc,

you mean besides using a heavier oil?

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