Yep. I understand. I did not phrase my previous post well. I think you were saying that the full Grp IV and V oils will not be damaged from exposure to 300F+ oil temperatures and will recover from that temperature repeatedly and continue to perform essentially as if it had not happened. The heat related low oil viscosity versus engine viscosity requirements is a seperate issue. Correct?

One has to wonder what the oil pressure was in a 1986 Mercruiser engine with 1986 oils at 300F+ oil temperature.

Depends on the viscosity of the engine oil.

If you ran at those temps, a multi-vis 20w50 would THIN LESS, therefore be more viscous (thicker) than a straight 50.
The same would apply to 40vs10w 40 or and multi-grade vs the straight weight version of the 210 side.

It has nothing to do with the "year" of the lubricant.
Viscosity is viscosity, be it 1986 or 2009.

Ken

I thought I read on this thread that over the years the oil grade rating systems have become more and more performance stringent resulting in better and better performance out of the oils. That is what I ment thinking that this meant that an S_ grade in 1986 was not as good an oil as an SL is today. Is that incorrect?

Not sure if this is the right place to ask this, but, what oil does would be the best to run in the Mercury Racing 525. Also drive lube. I'm running Bravo X drives behind the 525's, so I want something that will help with the extra HP. I plan to change engine oil and drive lube every 25 hours. (That was the advice from the guy that installed the engines for me.

Yeah,
I posted it on another site.

If Mercury endorses 280F oil temperature as OK in their engines what is the resulting oil pressure that by default is also OK in Mercruiser engines running at 280F oil temperature?

The best performing oils from an anti wear standpoint were SG,SH. SJ and SL the levels of anti wear have dropped, however the oxidative stability of SL have improved over the SG,SH rated oils.

Your oil in 1986 had more anti wear than the current oils of today.

Ken

Can't answer that question, too many variables.

Oil viscosity, bearing clearance, different oil pump, etc.

Ken

I run a synthetic/petroleum blend motorcycle specfic oil 20w50 and a full synthetic 75w90, GL-5 gear oil in my outdrive.

I change every 20-25 hours.

Ken