Hi,
m21, Jim - why change now? Run the excellent oil you have in there now until the next OC is due and change it then!

Remember that M1 15w-50 is a very high quality product that is suitable for annual or 12k miles oil change intervals when used in the correct ambient range - from -15C to 40C+

Enjoy - regards

 

Doug,

Thanks very much for the detailed answer!

And thanks again for your commitment to providing invaluable information to our 928 community.

 

Doug, thank you. It's really wonderful to have someone pay this much attention to the Porsche 928 engine oiling. Say ... do you have thoughts on gear oil? What have you been using and what have your results been?

Best,
Heinrich

 

Sniper,

I changed to this about a month ago, before a track event. Immediatley it seemed smoother on start up. No problems at the track and $21 for a 5qt jug.

 

I think we can safely say "Myth Busted" Changing oil too often is simply not needed or even good for the 928 ...

 

I agree Jim, but what % of the people know, or will believe this? I have talked to a few guys at my office and their remark is 'better safe than sorry'.
Hats off to Doug for the great knowledge he brings here.

 

My favourite show

 

James , Yes the power of ADVERTISING ! .".Safe than Sorry" " Pay now or pay later", So do the guys in your office also only use 1/4 of their tires before thay replace them ? Do timing belts at 15,000 miles instead of 60,000 ,replace brake fluid and coolant every 6 months ...

 

Would it really surprise any of us if they did?

LOL

 

They do what they're told.

 

I still believe that there is a potentially very lucrative class action law suit against the JIf /QUICk/INsta lube guys for "recommending" too frequent oil changes.

 

Hi,
Jim - I agree! Oils are a diminishing resource we need to conserve them by being sensible! The subject oil in this post would probably have lasted another year - but for me 12 months was enough!

Heinrich - thanks for your comments!

OTHER LUBRICANTS - 928

POWER STEERING
A Dexron 3 ATF (Dexron 2 is long superceded) is called for here. Any brand will do the job OK!

If the rack HAS JUST BEEN OVERHAULED a synthetic Dexron 3 ATF# will improve steering "feel" and will run slightly cooler. Do NOT use a synthetic ATF if the rack has not been recently overhauled

AUTO TRANSMISSION (3 or 4 Speed)
ATFs are the most complex of all fluids used in any car - even the basic ones are semi-synthetic. In a 928 a Dexron 3 certified ATF is all that is needed.

A fully synthetic Dexron 3 ATF# will work very well indeed. The correct choice of a fully synthetic ATF will improve the 928 Auto's change characteristics for the better and substantially reduce operating temperatures

MANUAL GEARBOX (Trans-axle)
The 928's trans-axle calls for a "simple" mineral GL5 75w-90 gear oil. Time has overwhelmed this specification and a synthetic GL5 75w-90* oil will usually improve the gearshift's "feel" - especially when cold - it will also run much cooler!

However, this is an area where perhaps a little caution is needed. Many car makers now specify special gear oils in order to mask poor design or production shortcomings
A 928 does not need these!

Some gear oils from a number of specialised oil blenders such as Specialised Formulations (http://specialtyformulations.com/) may work well as a temporary "fix" in a tired box

DIFFERENTIAL
The same comments apply as for the manual gearbox! (A hypoid SAE90 gear oil was once recommended - this oil is now long obsolete)
A special LSD additive or oil is not needed!

ATF & GEAR OILS (personal experience)
#ATF - I have used Castrol's excellent Transmax Z synthetic ATF for many years in a wide variety of cars and trucks - manual and auto. Due to its formulation it is a perfect fluid for all Autos used in a 928. It is Dexron 3 and Euro Approved by MB, MAN, ZF, Voith, and etc. It is also suitable for a four year or 100kkms OCI in a 928

It may be re-branded by Castrol for sale in the US - it is a very light green colour

Other Dexron 3 synthetic ATFs from the major Oil Companies will work well too - look on the container for Approvals from the above Companies (MB, ZF, Voith, etc) though as the frictional characteristics are important

*Gear oils
I have used the following GL5 synthetic gear oils for many years with great results;

Mobil 1 75w-90, and,
Castrol's Syntrax 75w-90

Both of these oils have repeatedly done 1m kms (four/five years) without change and with ease in the differentials of my heavy trucks (500hp, 100 000lbsGVM). They have both performed the same in identical conditions where the average oil temperature is around 95C. Used Oil Analysis (UOAs) have shown them as still suitable for further use at 1m kms (620k miles) and in the case of M1, it is readily available!

Mineral gear oils will tolerate constant temperatures up to 120C (and intermittently to 150C) and they degrade rapidly at/above these temperatures

Synthetic gear oils will substantially increase these temperature limits and run cooler to start with - a great advantage over their mineral cousins!

Usually a 928 differential will run under 100C and operate mostly under 90C in normal use

Regards

 

This is my 1983 owners manual scan. They had synthetic oil, Mobil-1 being one, long before 1983 and the benefits were well known at the time.

In this thread I am hearing what is basically "engineering advice" that is contrary to what Porsche recommends for the 928. I am willing to take good adivce when it's given, but I am reluctant to do so unless qualifications are established.

Is that reasonable?
Is it reasonable to blindly follow a thread?
Is it arrogant to ask a question, and verify?

I hope everyone here takes the question in the spirit in which it's offered here. Does anyone have anything from Porsche, that they can scan or otherwise reference me to, that suggests a 15W50 Synthetic oil may "increase bearing wear" as I've read in this thread. Synthetic falls under the "fuel efficient oils" catgegory in the owners manual.

Please reference me to published information that suggests or states premium oils like Mobil-1 15W50 are not to be used, or are not recommended for the 928. I am reluctant to change based on an "opinion" even though it may be well qualified, and I simply ask for the back-up to validate this opinion.

Sincerely,

P

1983 928S 5-speed

A couple other porsches

 

Read the ENTIRE thread and do some research on Doug Hillary's credentials and make your own decision like many of us have.

 

don't make an assumption I didn't read the entire thread, or that my reading comprehension skills are lacking, or about my knowledge of oils. I'm a seasoned enthusiast with many years under my belt.

Since I've built millions of square feet of construction under my signature over a 30 year time frame, I have a methodical policy when faced with written facts. I love opinions, and know the world goes round because of them, however, I like to verify the information before acting upon it, or perhaps recommending it to a friend. Naturally, you'll understand, that if I put my signature on the documents, I could be liable for the failure of the construction, so this is a responsible and very careful method of looking at data.

So now that you've read the entire thread and made up your mind, here is the pop quiz for the morning. Just two questions:

1. What is the elequent writers credentials (is he an engineer, an enthusiast)
2. Where can I verify what he says (give me reference to one document put out by Porsche, that backs up what this eloquent gent is saying).

This is absolutely NO disrespect, but I do not believe it is valid to use an oil analysis by an individual, as careful as it has been, to change oil type in a manufactured product because it (only) represents data on his single test. How does the individual know a different oil other than the one he is using wouldn't do the same or better? Fair question? I think so.

All the readers of these threads, perhaps you know something you can share (from Porsche). My dilemma, is I"m looking at the owners manual, and then I'm looking at an eloquent and well intentioined test report by an individual. In order to make a decision I need some basis for comparison (because in my research and articles, including interviews with oil tech representatives, I did not get the same information).

Regards, P