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Lubricants for the Porsche 928

This informative article has been written and compiled by Doug Hillary. Just part of his extensive experience includes: ..

  • Automotive Engineering - Trained by BMC in NZ and England (1957-1964) Included the first export Mini prototype's development in 1959.
  • Caltex-Chevron Copenhagen Denmark - operated a 'Quick Service Vehicle Development' Training Centre.
  • Technical Trainer for the NZ Trucking Industry - Road Transport Industry Training Board.
  • Alex Harvey Fellow '75 - Heavy Vehicle Development/Programmed Maintenance (GM, Cummins, Leyland, Daimler Benz, Volvo - worldwide).
  • Senior Executive Officer - Australian Road Transport Industry Training Committee.
  • Self employed since 1988 Road Transport & Training Resources P/L (incl 1989).
  • Management Consultancy Truck Driver training etc.
    Initial developer of 'TruckSafe' format.
  • Truck Fleet Owner - Interstate Includes;
    Lubricant's development with Castrol and Mobil, Risk Management with all Insurers, Workshop & Vehicle Management.

Doug's years of experience in the 'Industry' (and ownership of his '89 S4) has given all of us in the 928 community an excellent tutorial on this often queried topic. Many thanks Doug for taking the time and sharing your vast knowledge with us. - Leonard Zech, Webmaster.


Many thanks Doug. Had not heard the term 'Barrier Additive' before. I found this site which gives a good thumbnail summary/addition to your info:  - John Cumming '89 S4



1 - Firstly, Oils ainít Oils

2 - The Engineís Oil

3 - Oil Type - Mineral vs Synthetic

4 - Oil Specifications - Ratings

5 - Oil Viscosity - (thickness)

6 - Oil Consumption

7 - Oil Pressure - Oil Flow

 8 - Oil Cooling

 9 - Oil Filter

10 - Oil Change Intervals

11- Trans-axle

12 - Automatic Transmission

13 - Power Steering System (PAS)




The subject of lubricants for the Porsche 928 is both complex yet really quite simple.

Complex because of the extensive range of modern oils available - a truly bewildering choice.

Simple because it is all written in the Porsche 928 Driverís Handbook - and it has been from new.

A basic understanding of lubricants and the 928'e engine might help make the complex part simple!

A 'Religion' for some!

Many people treat their automotive engine oil choice as a 'religious' issue. They have their own special brands or brews. Or they use the brands and types recommended by so-called 'experts'. Sometimes the most likely choice circumstance is simply that advertising played the major role.

Sadly, except at the very extremes of racing or rallying there is actually very little difference between the various brands and types of oils - both mineral and synthetic. As long as they meet the API and/or ACEA standards and have Motor Manufacturerís Approvals they will perform the same task.

Only at the extremes of racing or rallying where special 'brews' or formulations are prepared by Oil Company Chemists (and their additive package supplierís Chemists too) for specific engine applications lubricantís may almost perform miracles. Sometimes these oils may be prototypes of new products to come on the market later.

There are no magic oils!

No magic elixir lubricant(s) exist despite the many claims otherwise. Yes, some oils are marginally better than others and in a general sense you get what you pay for. Ester based Group 5 synthetic lubricants (sometimes using coconut oil 'esters' etc. and other more advanced substances) certainly have some benefits. They are quite expensive and the benefits occur mainly under severe heat stress and at temperatures below those experienced in Australia. Some synthetic oils do minimise wear in valve train components but this only shows up after many hundreds of thousands of kilometres of use - much longer than most people will keep their cars in most cases.

Some synthetics do allow extended drain intervals - but Porscheís recommended drain intervals are already long enough even with the 'normal' recommended mineral oils - so thatís not an issue for us

As with most things generally however the most expensive lubricant is most likely the better quality lubricant! Simply though it may not be the most cost effective for you.


No 'supa-dupa' extra additive such as Slick 50 etc. will extend the life of an engine. They may reduce oil consumption or reduce noise - but always at a cost. No independent research has ever conclusively proved that the likes of Teflon actually works at all in engines. In fact DUPONT Teflonís inventor says that it doesnít despite some manufacturers advertising to the contrary

Some sophisticated chemical additives such as ZDDP, MoS2 and MoDTC however do work very well - at the levels already carefully blended into many high range lubricants and hence the higher prices. With these chemicals it is not a case of the more the better - in fact it may be the reverse. So donít add anything to your oil - it can do more harm than good. Some may actually pollute exhaust catalysts or cause extra deposits on pistons, ring lands or cause oil foaming and etc.

More, and very complex chemistry is being blended into todayís lubricants than ever before - and there is more to come. Some new built-in components of the latest base oil formulations and additive packages are truly amazing performers! They are needed in todayís and for tomorrowís engines - the fuel economy, emission and technology requirements demand their continuing development

You should not add any extra additives and spoil the Oil Chemistís carefully structured brew.





As examples and for your interest I use the following lubricants in my 1989 928S4 Auto:

Engine - Mobilís Delvac 1 5w-40 CI-4/SL - a HDEO mixed fleet fully synthetic diesel oil.

I do a UOA every six months and the OCI is annually or at 20k - earlier if the UOA determines this

Auto Transmission & PAS - Castrol Transmax Z synthetic Dexron 3 rated ATF
(a "lifetime" fill - 300 000kms or three years)

Diff - Castrol Syntrax 75w-90 synthetic GL5 gear oil
(a "lifetime" fill - 300 000kms or three years)

If my car was a manual 928 then Castrol Syntrax 75w-90 would be in the trans-axle

Doug Hillary '89 S4

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