Hey all, I've got a 1993 Baja 240 Islander with the original Merc 7.4 in it, at about 800 hours. This thing burns a LOT of oil, about a quart every 4-5 hours or so. There's blowby out of the valve cover breathers, and it's definitely noticeable smelling the oil burning if going slow or downwind. It doesn't leak, the bilge is *mostly* clean and dry. I did a compression test and got ~122-125 psi on all cylinders except 1, which read ~110 psi. Obviously that cylinder isn't spectacular, but considering the boat runs GREAT I don't plan on fixing that any time soon. Knowing that there's only one cylinder low on compression, and the plugs all looked pretty good and boroscope in the cylinders all looked great, I'm thinking the bottom end can't be enough of a problem to burn *that* much oil?

As an alternative, I'm considering pulling the heads and doing a valve job, thinking some valve seals may be shot, or possibly even head gasket letting oil out into the exhaust water? Additionally, there's some oil pooling in the bolt recesses on the valve cover; I'm not sure if this could be the blowby oil mist coalescing back down to liquid (it does seem to be mostly around the breathers), OR if it's likely a failed gasket. I'm curious if the more experienced minds here think I may be on the right track with pulling the heads, or if that may be a waste and I should hold off until I want to do the bottom end too?

Thanks in advance!

If it's got that much blow by, it's in the bottom end. Needs a leak down test.

Also test your coolers! You never know!

I’d replace with a 540 and Scx-2 right away !

No disrespect meant here, but with a boat that old and motor that uses some oil I would just leave it alone. Do the valve seals if you are doing it yourself is an option but most every other “rebuild” choices are much too costly. On the other hand if you plan on this boat being your “forever boat” look at replacing with a “drop in”. Some good deals $$$ on those.

agree with sonic, if the plugs all look decent then it is not a single bad cylinder burning it but seems that most is blowby that you are seeing and smelling. I would just run it till it shows signs of being too tired and just do a swap with an already fresh engine to limit down time. the engine I had in my jet boat was a junker with rust pits in the cylinders so bad you could break a fingernail on them. it ran for two years at WOT everywhere before it finally broke a ring. in that time I was building a better engine for it and it was ready to go again.

Valve seals will not cause that much oil consumption. If it has blowby then there is your answer. The poor thing is probably just worn out. 800 hours is quite a few

I agree with the others. Either keep running it like it is or figure on a replacement. Pulling the heads on 30 year old engine with 800 hours on it is just asking for trouble. The heads will not "let oil into the exhaust"

Is it really? This is a question that has been asked from time to time, with some saying to expect up to 1500 hours. THT has stories of fishing boats with 454s going longer than this even.

Big difference between a fishing boat or cruiser type running around at half throttle for that many hours and a hot rod boat running around WOT or close to it.

800 hours in a performance boat is like 50,000 miles in a truck running fully loaded up a long hill that never ends.

Also big difference between fresh water and raw water cooled. A 33 year old raw water cooled engine is going to be in terrible shape as far as corrosion in the water jackets. Half of the head bolt holes will need Timeserts, etc etc etc. I have taken enough of them apart to know better

Hey all, thanks for chiming in! Yeah, I do think I'm on the side of keep feeding it oil and run it until it stops. Perhaps in the next few years I can go with SB's 540 ! But I am... appreciating the puzzle that this motor is :P Something I hadn't considered is those of you who mentioned touching anything might be asking for trouble. Truth be told, this motor has been incredibly reliable for me. Throw a quart in every morning, and I've had an enjoyable ~130 hours on this boat without incident since I bought it 2 years ago.

I just spent a whole week on this boat, reupholstering, adding tabs, adding more speakers, annual maintenance, gelcoat repair. I'm a bit spent for now. Next month I'll get back into it to finish up some projects before summer.