Ok so I decided to switch over to amsoil this year because it was actually cheaper than Mercruiser semi-synthetic. The only amsoil I could get for Marine use and was 10w40 full synthetic but Mercruiser recommends 25w 40. Think this will make a difference? What are you guys running here in the Great Lakes area?? Oh I run 454 magnum MPI's with about 400 hours on them now after this year. Alright spill it!!

Amsoil make a marine "dominator" oil that is 20/40 I think? It's readily available, you should have no problem finding it

Yes, Dominator oil.

I run the 15w40 Amsoil for marine/diesel motors.

http://www.amsoil.com/shop/by-produc...ont%2fame.aspx

I have been using the 15w40 diesel oil for years. I switched this year to their 20w50 z-rod oil. Check it out on their website.

20w50 Z Rod

Honestly anything you run that has a 40w on the end will be fine. Even straight 40. I agree go with whats easy and cheap. There is no proof on what is better just piece of mind!

I personally run Valvoline Racing 50w conventional oil only $5 a quart and carried at all 3 local parts stores. Trouble free for 230hours 8psi procharged 500EFI's

I use Amsoil in my Diesel Rams Rear diff and the Imco SC drives 75/110 Severe gear

Mobil 1 V Twin.