1979 merc 90 hp prop leaking oil

[woffie27]

my 1979 90hp merc is leaking oil out of the end propeller and at the base of the propeller. I'm wondering if it could be the trust hub that went bad or is it something else? also is the trust hub the same as the rubber hub, and would the rubber/trust hub make the prop leak oil. the oil is light and leaks out when I turn off the motor. anyone that can help, thanks

 

[WillyBWright]

Re: 1979 merc 90 hp prop leaking oil

If the oil is like the gearlube in the gearcase, then it's a seal leak. If not, it's probably unburnt 2-stroke oil. That can come from a carb problem, fuel pump problem, or just as a result of a lot of low speed operation.

The thrust hub is the washer you put on first, before the prop. The prop hub is a rubber cushion pressed into the prop. Neither should have anything to do with your problem.

If it's gearlube, you could have either a bad propshaft seal(s) or a bad driveshaft seal(s). Could be a combination of both. It's either leaking past a bad propshaft seal, or the driveshaft seal is bad, allowing some water from beneath the water pump to be forced into the gearcase, forcing gearlube past the propshaft seal.

Considering it's age, if the gearcase hasn't been resealed, it's way past due.

 

[JUSTINTIME]

Re: 1979 merc 90 hp prop leaking oil

put some on your finger and smell it
gear lube smells nasty

 

[Clams Canino]

Re: 1979 merc 90 hp prop leaking oil

Drain the lower and look for water. If gearlube is leaking out, lakewater is getting IN.

-W

 

[woffie27]

Re: 1979 merc 90 hp prop leaking oil

thanks all for the info, I think it is coming fom the carb. how much oil is a normal amount though? looks like it is leaking like a 1/4 of a cup at the most.

 

[OldMercsRule]

Re: 1979 merc 90 hp prop leaking oil

BTW when you drain the lower unit, the gear oil, (which smells strong as has been stated), gets milky white if there is water intrusion. If the oil is from "the carb" it will not smell strong. Re read Willy's post. Your motor is an inline six, (I would guess), and that vintage did not have oil injection. That means that the oil is in the fuel and Willy's post should explain the potential problem. Mix your oil 50 to 1 and shake the can, (if it is a six gallon can), to make sure it is properly mixed. If you idle a lot make sure she gets a good WOT run to clean her out, and you may want to consider decarbing the engine at some point. JR

 

[Clams Canino]

Re: 1979 merc 90 hp prop leaking oil

Decarb the inline six once per year - period.

-W

 

[WillyBWright]

Re: 1979 merc 90 hp prop leaking oil

If you have portable gas tanks, only close the vent if the tank doesn't have a hose attached to it. Pressure can build up inside and force gas through the carbs. The gas evaporates leaving oil.