I have twin built motors (496's) Dynoed at 550 hp each in my 38' Scarab KV the owner before me ran 40weight valvalene racing oil.I always ran 20-50wt in my other boats seems a little thicker oil? but with built motors I'm nervous about changing oil weight any feedback would be great!
Chuck.............

I ran valv 40 racing in stock 502 mag's for 7 yrs without a prob. Merc sez straight 40 in my 502 1993....25-40 in the new 525's.

My opinion, stay with the valv 40 race. Not sure where your climate is. That could change things....

I live in upstate New York,this summer has been really hot and humid and was concerned when I see my oil temp climb more than I like to see when running full throttle can't remember what it was but 230-280 sticks in my head? without going out and looking at my gages to refresh my memory it comes back down when idling,didn't know if that was to hot? about what oil temperature should a motor be running about 5000rpm's say about 15-20min? also dose a high performance motor use some oil if driven hard for a day? I know my last boat had a 454mag in it and the book said it is not uncommon to use a quart of oil every so often?
just some questions I have with this new boat it was a big jump from a 24' outlaw with a single motor to a 38' Scarab KV with twins(big motors) I figure this is the place to ask the questions.
Thank You! Chuck.............

not sure what oil temp should be in your motor set up.
yes you will use some oil, that is common.

230-260 should be ok, 280 may be a bit hot.

I assume these ar carb motors, not EFI.
What did the previous owner say? If he was running Valv Race 40, I would stick with it.

re-post in technical section, someone should be able to help.

in my 496 i run mobil oil syn 5w50. my oil temp at wot is 220

I've never had anything other than straight 40 weight in all my engines, Pennzoil, Quaker State, Valvoline, Havoline and most recently Parts America's own brand at $1.29/qt. After 13 years, there was no sludge in the original engines, looked like they had 100 hours on them. A blown head gasket was all I had go wrong.

You're asking a religious question. Whatever you use, 40wt or 20-50w, change it and the filter every 35 to 45 hours, religiously. More frequently if they're supercharged and always running hard, something like every 25 hours. Cheap insurance.

sorry to Hi-Jack, I have just bought a 22' Scarab with the 310 hp 454. Im gonna change the oil in it and wondering what you guys think about oil for it. I was thinking about using 15w40 mobile full synthetic. The other owner was using quiksilver 20w40 i think.

I run 40W Castrol Syntec Blend. Previous owner was using straight 40W, and I would be running Mobile 1 50W fully Synthetic but I don't want to start an oil leak by switching to a fully syn oil on a 350 hour engine.

I agree with Keith though. Really doesn't matter what you decide on as long as you change it regularly. I do every 25-30 hours no matter what; plus once before I put it away for the winter and once right after storage (just a waste of oil basically but I don't like that old oil sitting there for 4-6 months with no use.)