I use Pennzoil Marine Sythetic GL-5 does the job

I like the RedLine stuff.:cool:

go with the red line
 

go with the redline its great ,,even in trucks and cars

If I were to switch to a synthetic drive oil any suggestions on what to flush the drive with to remove the residual oil ?

Good question, I was wondering it a flush was even needed. Is the Redline oil compatable with the minor amount of Merc oil that remains in the drive when drained.

Rick

Yes the red line is compatable !! If you can stand it pour some through the drive to flush out the merc . It helps its just not criticial ,,enjoy

blown1500, I was just wondering what advantages you have noticed in cars and trucks. What about the trany also? I was thinking of trying some in my truck because it gets really hot when pulling the boat on hot days. I have to pull 50 mi. over alot of hills to the water wonderland. I am really underpowered and it is floored up every hill. Maybe I should install a whipple in it also.
I use Redline in my outdrive and might try it in the truck if it helps.
Thanks,

I've switched to synthetic oils in all my cars,trucks,bikes and boat. A lot of my stuff will sit for months, and I can tell you at start up there is always an oil film to protect parts, the engines seem to run quieter as well. The only place I've not seen an improvement is in the 4 spd in my 68 Charger, I think these old boxes need that heavy weight dino juice. my .02

Duh, sorry I forgot to tell you. I'd stick with a racing oil like Redline, Torco, or Royal Purple.
The general automotive oils just lost a great deal of their lubricating packages, due to the tigher emmisions requirements, it seems the Cats can't take the Moly, Phosphrous, and Zinc that they used to put in.

Thanks for the info Sonic. Do you use synthetic in automatic trany also. I know that heat is what kills them and maybe synthetic would help to keep it cooler, as long as the clutchs don't slip and create more heat.