Mercury 500 50hp Strange Dripping from Prop, + Cutting Out When Throttling Down

[Liopleurodon]

Complete newb to outboards, bought a 75 Starcraft SS last year. Came with a 50hp Mercury.

Worked fine all last season, with one exception - when throttling down, it would cut out, but then would start back up at an idle as though nothing happened.

At the end of the season, when I winterized it with RV antifreeze, the prop seemed to drip with a thick, dark oil. To be precise, it came from in between the prop and the lower unit, not the center of the prop, and basically dripped down the skeg.

It felt thick to the touch but there was honestly very very little. About one or two drops on the floor. My guesses thus far are a.) gear oil (bad?), b.) dried out fuel+oil mixture (not bad?). I don't think it was the anti-freeze, but I can't say that definitively. I actually didn't notice it until I pulled the motor.

Is this familiar to anyone? To give background on use, I did scrape bottom on a number of occasions, but it was generally soft. I also did not see the dripping until after I winterized the boat. I have not seen any subsequent dripping, just the first few drops.

Will be replacing the transom shortly and hoping to get back out on the water soon. Thanks in advance for the advice!

 

[GA_Boater]

Re: Mercury 500 50hp Strange Dripping from Prop, + Cutting Out When Throttling Down

Drain your lower unit and check for water. If gear oil is coming out, water is going in. Most likely the drip is unburnt 2 stroke oil. As far as the stalling it might be time for fuel pump/carb rebuilding - and maybe not as long as it runs fine other-wise. Idle might be set too low.

First time I heard of using antifreeze to winterize an OB. I just drop it down so water can't collect and freeze in the prop hub.

 

[Liopleurodon]

Re: Mercury 500 50hp Strange Dripping from Prop, + Cutting Out When Throttling Down

I have not run any additives in it besides fuel stabilizer, and I know the original owner used a fuel oil mixture closer to 32:1 vs 50:1.

Would a good first step be to run seafoam or other additive to clean the carb?

I'm wondering if there's any way to test the oil - would rather not disassemble if not necessary (though it may be easier than I think - haven't tried without a manual.)