View Full Version : Oil on intake manifold

07-21-2012, 06:29 PM
'89 Prostar, Indmar 351. Put 25 hours on boat last week while on vacation, ran great. Cleaning up today I noticed a puddle of what appears to be oil on the intake manifold. There also appears to be some on the backside of the carb.

I did change the oil last week - it was slightly over the full mark at one point, I've since drained it down (maybe a 1/2 quart).

Not a noticeable leak anywhere else on the engine, top or bottom.

Ideas on where this is coming from and a fix?




07-21-2012, 06:38 PM
Had that happening on my engine with TBI thought it was bad valves. Ended up being both bad valves and pistons that had melted.

I would try a compression test.

07-21-2012, 07:01 PM
Jack, It may be the pcv valve is stuck.give it a shake and see if it rattles, it should. Also check the inside of that hose and that will tell you if it is going through there. There is quite alot of vacuum there and sometimes it'll pull oil and/or vapor especially if it is running at the upper rpm's
All the best,kent

07-21-2012, 08:38 PM
PCV VALVE i think also, the hose from pcv to the bottom of carb should be a tight fit.

07-21-2012, 09:55 PM
Thanks for the replies! I will check the PCV - I replaced it last year 'just because'. I've read that most PCV's today are pretty junky - I think I got mine from Advance or AutoZone. The hose from PCV to carb is original - fit is extremely tight at carb base. I'll look at it for signs of oil passing through.

I was thinking the overfill of oil, combined with a week straight of pulling skiers, wakeboarders, and tubers - was causing the oil to escape from somewhere.

Also, I checked the four bolts on the corners of the carb plate. The one closest to the oil puddle was pretty loose....as in not snug at all, and there was oil around it too. I don't know how tight it should be. I know you can compress some gaskets to the point they will not seal, so I just snugged them down.

At this point, I don't think it's valves/pistons. I just changed plugs, they looked great, boat runs great, doesn't use any oil, doesn't smoke, very well maintained and just reached 400 hours.

08-13-2012, 02:15 PM
Drained out a little oil (to full mark) - snugged down bolts on carb plate and no more oil!