Do i need to repair my boat engine?
i have a 1992 48 horsepower evenrude and i just found an oil leak coming from the gearcase. i looked for where the leak was coming from, hoping my moter doesn’t have a crack and it was coming from the bottom of the prop. i don’t have much money and i really like going out on my boat so i can’t really afford to buy a whole new moter. how should i fix it. I think its burnt oil from the power head making exhaust residue because it is a dark black. if this is true would i need to fix it and if i do then how?
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January 24th, 2010 at 7:53 am
relax, unburned engine oil dripping from the exhaust is not uncommon. It has that dirty dark appearance because of all the carbon build-up in the cylinders, ports, exhaust tube, etc.
Easy enough to find out if it’s gear oil — just drain the gearcase; if the oil has a streaky or milky appearance, it’s got water in it.
Assuming it’s engine oil, here’s what to do:
First, if your spark plugs aren’t Champion QL78C gapped at .030, change ‘em. I have nothing against other brands, but your engine was built around that plug and that plug is what will make it happy.
If you do a lot of trolling, then widen the gap to .040, and make sure you finish the day with a nice long run at WOT. These motors are bulletproof, but they’re tuned to run flat out, and need to do so in order to keep carbon from building up in the cylinders.
Add a decarb additive to your gasoline. I always add an ounce of Seafoam per gallon. Mercury, Yamaha and OMC all make good stuff too, but they sell Seafoam at my local car parts store, and it’s great stuff.
You need to be making 5000 to 5500 RPM at WOT with a normal load in the boat. Any less than that is lugging the motor at all throttle settings, and lugging promotes coking. Dropping down an inch in prop pitch will add about 200 RPM.
Clean the carbon out of your motor. The manual says to pull the cylinder head and manually clean the cylinders. But here’s a better way:
You’ll need a couple cans of a a spray decarb solvent product, such as SeaFoam Deep Creep, OMC Engine Tuner, Mercury Power Tune, or Yamaha Ring Free. I use Deep Creep.
Run engine at fast idle, with engine running and warm, slowly spray liberal amount into each carb. Its gonna smoke up the place. Spray for a couple minutes, now spray a larger amount into the carb(s) until engine chokes out and stops.
Remove spark plugs and spray the decarb product liberally into each cylinder, install the spark plugs, let it soak for an hour or more.
Spin the engine with spark plugs out to blow out all the crap that’s in there, then start the engine and run at medium throttle, or if at the lake, run it at full throttle. It won’t hurt to spray some more through the carbs. Run it for at least 10 minutes to flush the crud out of your engine.
Now remove and clean, or replace the spark plugs. It works well to do the spraying, the night before you go to the lake.
This way you can let it soak overnight, and run at full throttle at the lake.
Don’t do this in front of the garage door or the house, unless you want it covered with greasy black crud.