I was talking on the phone yesterday to an reputable Amsoil Wholesaler and was discussing using Amsoil in my 5.0 Mercruiser. I asked which one to use and he stated the 10w 40 would be good. I asked about the 10w part because mercruiser is 20. He stated that is a mercury marketing scheme and 10 40 would be better.. Any thoughts.?

Chris

I asked the same questions with an Amsoil rep/researcher I know from one of the Mustang forums. Here's his recommendations. This was based on the Merc SAE reccomendations and the Amsoil filter is the same as the Wix filter. If you go to Amsoil.com you can go to the wholesale page and get a 20% discount with a wholesale membership.

Hope this affirms what you were told.

Amsoil AMO 10W-40

or Amsoil RD50 15W-50

Amsoil EaO59

Blueabyss, the "W" in an oil's viscosity means winter. It is an indicator of the oil's ability to flow in cold weather. A 0W oils flows better than a 10W oil in below freezing temps.

Your probably do not boat in sub freezing temps, so the first number is a moot point.

This begs the question, is a 10W oil better at 50 degrees than Merc's recommended 25W40?

If there was to any difference in the two viscosities it would be when you first start the motor for the day. The 10W would pump easier.

Would it be noticeable, not at all. After all, Ford used to recommend a 15w40 for the Powerstroke is all climates, this included temps below freezing.

I would be more concerned about the second number, the higher the number, the more film strength the oil has, the more pressure it can carry.

As far a a Merc's 20W oil being a marketing scheme, I would say no, it is what they recommend.

I personally run a 20w50.

Ken

If your 5.0 Mercruiser is calling for a SAE40 weight - the Amsoil guide is reccomending the WCF... not that the other 40wt will not be more than adequate. That said the Amsoil guide also gives the same WCF oil as their reccomendation for the Mercury Racing 525, 600 and 800SC engines but I would personally be bumping up to their Dominator lineup

http://www.amsoil.com/shop/by-produc...ke-marine-oil/

Personally I run Amsoil in everything I have - always have, always will (except when I have to maintain "new" warranty by running factory oil - obviously)

Running a 15w-40 or 10w-40 is always better for any engine when it is cold. Even if your block temp is 50 or 60 degrees in the morning when you first fire it up. More wear happens at this time than any other time. I run Amsoil racing oil 15w-50 in my 515 BBC, and it even sounds better when starting it up cold than it did with 20w-50 in there.
The thinner the oil for a colder engine the better, its just good insurance to protect your motor during the starting of your engine and first warming it up.

I run
amsoil Diesel and Marine, I can't remember the visc.