I did some searching but did not find this well described. So I'll take a shot . I have a 99 353 with 502s. about 450 hours. Runs strong ( about 70-72) and has been super reliable. Always has had dino. I notice that oil consumption increases as the season draws on ( I run about 50 - 60 hours a summer) and for the first 30 or so it is pretty modest ( maybe a half quart each motor). Later in the season I need a quart to close the season out. Would converting to M1 ( say, 20-50) help keep the oil stable and keep consumption down? Is converting to synthetic a mistake after this many hours/years? Any other syn issues I should consider? I know that 502s tend to use more oil, so I expect some. Thanks for the advice .

Any information I've read indicates that a switch to synthetic will increase consumption noticeably particularly in an older engine.
I would, instead, suggest trying different brands of dino oil, since oil consumption does vary by the brand.

You won't encounter any problems switching to a synthetic oil. 15W50 Mobil 1 is a good choice. You should see a reduction in oil consumption with the Mobil 1.

First off, I use Royal Purple 20 - 50 in my HP500. Lots of opinions on what is the best oil to use, just like what you would run in your car. Here is a ton info on oil break down by brands and also what filter to use.

Questions 9 - thru 13 should answer whether it can used in older engines and about consumption. 1st link from Valvoline:

http://valvoline.com/faqs/motor-oil/...tic-motor-oil/

Hydrocruiser has a lot of info but long read:

http://www.offshoreonly.com/forums/g...brication.html

http://www.offshoreonly.com/forums/g...brication.html

First of all, any oil related thread is going to get a million opinions....



That aside, the 502 is essentially a truck engine from GM that guzzles oil down so fast that it really doesn't matter. We're not talking about some exotic Ferrari / 911 turbo here. Just put some quality oil in her and go. I'd stay away from switching between conventional and synthetic oil, but past that just run what you are comfortable with and can easily purchase. Changing your oil regularly probably makes more of a difference than what oil you use. So there's my opinion - fwiw.

502's are known to use a little oil, just keep freshening it up with reg oil changes and keep her running, I like to change mine every 25 or so, I was worried as hack when I got it but its just the nature of the 502 to use some.