Dennis,
He also asked, "Which should I use in a marine engine?". I know that’s a loaded question with many right answers. What is your personal preference? I use straight 40W in my 454 mags. I like the answer to the first question. Very informative.

I have an interesting topic for your magazine. WATER PRESSURE! That is the most confusing problem I have ever encountered. Do a search in this forum and see how many times this topic comes up. And in direct relation to that is the topic of circulating pumps failing with 50 to 60 hours on them. You can have fun with this topic. Heck if you do a story on high water pressure I'll subscribe.

Thanks,
Dan

Dennis,
Your answer is very informative. However, I wonder if he has an underlying question, what weight oil should he use if he does not choose Merc oil. Maybe you can add to your answer and include recommended oil weights. I know some may argue that it depends on the engine, but I think this question is referring to stock Merc engines since he is referencing the merc manual.

Rick

Looks good to me

Jon

'it is simply a blend of 25 weight and 40 weight oils."

I think that Merc Quote is a bit confusing. If you mix 25 and 40 without any additive wouldn't it be the same as using a straight 32.5 weight or of course the closest thing 30 weight?
Sorry I know you have to give a simple answer without getting way too deep in the subject but this does seem to be contradictive to the additive statement and why they are used.

Something else to ponder about.

If there is a problem with using synthetic oil and hyd. roller lifters why does GM use Mobil 1 5 -30 as the factory fill in all the LS 1 engines. This covers all Corvettes, & Camaros & Trans Ams built after around Sept. or Oct. 2001 when it also became the factory fill for them.

It is also the factory fill for the new Merc. HP 3.

Be safe,
Mark

Something else to ponder about.

If there is a problem with using synthetic oil and hyd. roller lifters why does GM use Mobil 1 5 -30 as the factory fill in all the LS 1 engines. This covers all Corvettes, & Camaros & Trans Ams built after around Sept. or Oct. 2001 when it also became the factory fill for them.

Mobil 1 15 -50 synthetic is also the factory fill in the new Merc. HP 3 engines.

Be safe,
Mark

Good topic and questions. I really dont understand how the OEM's can use Synthetic oil on new engines? Id like to hear an expanation of how they do it. I can see where they can manipulate the surface finish on the cam lobes and rollers to get them to hook up but what about the rings/cylinder walls and oil pump gears etc.

You answered part 1 of the question, but what do you recommend for marine use?

Also explaining the diff. between dino and synthetic is always helpful.

Depending how long you want your response to be you could get into performance engines and their oil requirements.

I know years ago, GM would fill the motor from the factory with a break in oil. That may not be synthetic in this case allowing the rings to break in.. New car no one notices untill the newness wears off.. by then you are putting in the synthetic and everyone is fat dumb and happy?
Just a thought..
I have heard cam manufactures recommend staying away from the synthetic on roller cams, but I believe it was the solid roller style. But then I have heard the opposite argument also..

Dennis, good article! Interesting questions raised and explored by the OSO'ers..

Dick

Thanks for the feed back and keep it coming. I think that with the response I am getting here I will do an in depth article about marine engine oils. Look for it next summer.
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE