Mid 70s Mercury thunderboat overheating

[Mercclunker]

I have a mid 70s Mercury thunderbolt that is over heating. I just put a new water pump in it, and she has a steady stream of water coming out. When the pump was changed, the oil was topped off. Any ideas on what would make it overheat?


Other problem is that when i push the throttle down, i cant get any really speed out of her. i just moved her from a heavier trihull boat to a newer bass boat hull. Not sure if just adjusting the throttle cables would fix it, or is the over heating and the throttle issue the same problem together.



PLEASE help, I have a tourney this weekend.

 

[Mercclunker]

Re: Mid 70s Mercury thunderboat overheating

Sorry its a 50HP

 

[Chris1956]

Re: Mid 70s Mercury thunderboat overheating

How do you know the motor is overheating? i

It is doubtful the throttle cables have much to do with your problem.

if waterpump is working fine, that motor should run dead cold at idle, and warmer at speed. Put your hand on the exhaust cover (port side of block) while idleing and make sure it is dead cold. if not, you have a waterpump or clogging issue.

 

[Mercclunker]

Re: Mid 70s Mercury thunderboat overheating

Ok it might not be overheating, but it is either smoke, or steam coming off of the side of the motor. its really hot to the touch after its been running for a while right under the power head on that middle section between the powerhead and the foot.

As for the throttle, does it sound like an adjustment issue. I push the throttle all the way down, and it just creeps.

 

[Dave1027]

Re: Mid 70s Mercury thunderboat overheating

Steam or smoke coming out the side sounds a lot worse than a simple adjustment. Might as well forget the tourney. I think you need to first figure out whats causing the smoke/steam. Do a compression test.