What weight of engine oil should I use for a 502 Mag
 

I recently purchased a used 272 Baja with a 502 and I couldn't find a lot of information (didn't get a manual with the boat) on the engine saying what weight of motor oil I should be using. I am boating in Ontario so the air temperature when on the water is in the 70 to 80 degree range. Can anyone offer some guidance on what is a good all round weight of engine oil? I have heard anything from straight 30 weight to 25W40.

Thanks

I have always used mercury 25w40. No issues.. but I have the 454 mags.. I have read that 502s usually use a lil oil, so some stp oil treatment could help too.

20w-50 Is what I run. The 502 likes thick oil (loose tolerances) . Just let the engine warm up before putting the hammer down. And yes it will burn oil! Keep a qt or 2 with you just incase

I believe Mercury now "recommends" QuickSilver 25w-40 4 stroke oil.. But that has changed with the oil market.

+1 QS 25/40 her whole life. They do burn some, keep a close eye on it the first few times out to get an idea on usage. They seem to vary a bit. Great motor.

I run 20W-50 in the 496.

Can't remember if I sent you the manuals or not. PM me.

After some reading in another thread. I think I am going back to a straight 30 weight oil. Been seeing some pressure drops after long runs I never had before untill I went with multi-weight oils.

I'm a fan of Rotella 15W40 diesel oil. I tried straight 40wt in my boat (the selling dealer recommended) and it drank it! Maybe a quart every other weekend. I decided to switch it to Rotella and it stopped using oil... It's cheap enough and always available.

ive been using rotella 15w-40 and K&N filters on my 502 mags for a few years now and don't notice it burning much at all

I would run a stright 40 or stright 50 w oil. Like valvaline VR1 racing oil or kendal. Dino oil. No need for synthetic since us boaters change it so often. No need for a multi viscosity since we only boat in warmer weather.