These are great writeups... (archive)

In general the mfg recommends the right weight oil for the way the engine was designed - that is the right viscocity to match the shear requirements at the specific internal temps and tolerances. A diesel, to use an extreme example, often has looser tolerances so using a straight 30W oil may be acceptable where using the same oil in a gasoline motor may cause the motor to run too tight and wear prematurely over time.

So, start with the mfgs recommendation... the problem that most of us have is that we know nothing about the life of the engine before we inherited it. In my case, I still start with the mfgs recommended weight. If I start to notice consumption getting above a quart per change interval (3K miles) and I am not seeing significant external leakage from crank, cam seals, oil pan or valve cover gaskets, (and can verify that there is not excessive positive crankcase pressure) then I usually go one grade heavier according to the season. For winter, I'll usually go to a 10w and for summer to a 15w. When selecting a multi-vis, I can't tell you where I heard it, but someone instilled it into my brain that going more than 30 points above the "cold" weight was not healthy (for the engine). As a result I try to stick with something like a 5w-30, 10w-40 or a 15w-40. I'll admit that my information may be dated on why the narrower range is better and that I have not gone back and re-educated myself as to why many synth oils seem to have larger ranges like the 0w-50 that Henkka was talking about. I have heard a lot of good things about the 0w-50 for new engines and so I thought I'd give it a try on this new motor that I'm going to be breakng in... means I may have to spend some time updating my understanding of oils before I can sleep at night (wrong!). Anyway, that's my unscientific philosophy on the subject.

Kevin

I found these articles to be very helpful... hope they shed some light on your questions. I am currently running Mobil 1 10W-30 in the cold Canadian north. I switched over last summer/fall from whatever dino oil the previous owner was using. As for how long between changes, I decided to do oil analysis to determine the change time. Currently have about 15,000 km on it and analysis still good. Have base line for new oil, then one at ~10,000 km and one at ~13,000 km and one due again shortly. Analysis shows all contaminants including dirt etc, (filter) and viscosities. Cost less than $20 CAD (~$13 USD) per run. I have the results on Excel if anyone would like to see how it is going.

http://www.pelicanparts.com/techarticles/mult_gas_and_oil/mult_synthetic_faq.htm
http://www.mr2.com/TEXT/OilFacts.txt
http://www.mr2.com/TEXT/oil_filter_test.html
http://www.audiworld.com/tech/eng9.shtml
http://www.audiworld.com/tech/eng12.shtml
http://www.audiworld.com/tech/eng14.shtml

'88 750iL

And I guess something like 5w-30 or 5w-50 (thin) (as opposed to 20w-50 (thick)) would be better if possible because it is relatively thin, but can withstand high thermal loads (especially 5w-50).

Am I right?

Follow Ups:

No no no nooooo Henkka 750i 04:40 1/29/2002 (0)

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