Hello Everyone, I recently purchased...

[joecaruso]

Hello Everyone,

I recently purchased a 1989 340 Sedan Bridge.  The boat is in great condition and runs great but I notice that the starboard engine burns about 1 qt of oil every 4-5 hours and it also consumes more fuel than the port side motor (it takes it a bit more throttle to run it at the same RPMs as the port side motor).  Some people told me to use marvel mystery oil, others said that is nothing more than snake oil.  Is this common for two identical motors (Mercruiser 7.4s) in a boat to perform differently even though they have the same number of hours on them (1,200)?   Is there anything I can do to help this motor (without rebuilding it)?

Thanks,

Joe

[Stu2]

With 1200 hrs and a lot of years. Oil consumption is normal start by running a compression test on all cylinders. I would also pull the valve covers and inspect this area for crud build up. And make sure the oil drain back holes are clean and flowing. Let us no your results. So we can give you some additional ideas.. Do you no if these engines have ever been rebuilt
Stuart

[Knighthawk]

Check out the products made by MotorKote. For friction reducer and others to use on your boat and trailer.

[Indiana]

We just bought an 83 340 Sedan Bridge and it burns more gas on the Port engine. Apply the same solutions?

[wingless]

Joe,

The compression check is a good starting point. Oil consumption is either blowby in the pistons, leaking past hard valve seals or external oil leaks. The external is easy to spot.

If the compression check is good, then it is possible to swap the valve seals w/ limited disassembly.

If the measured fuel consumption is more, then compression is also a good starting point. Assuming a carburetor engine, so the carb should be clean and properly adjusted.

The throttle cables need to be adjusted properly.


Indiana, welcome to the forum. Yes same solutions.