1985 150hp Black Max idles hot

[jimmydail]

New owner of a 1985 150 hp Black Max. Starts and runs great. Pushes a 18.5' Nitro ski and fish close to 60 mph. Runs cool at speed but heats up when trying to troll at idle for more than a few minutes. Any suggestions on cause and solution?

Appreciate the help. Great forum and members. My first post.

 

[Chris1956]

Re: 1985 150hp Black Max idles hot

I have had that happen on my MerCruiser. Turned out that the water pump impeller was bad. You might replace it, especially if it is more than two years old, or you hit some sand recently.

 

[jimmydail]

Re: 1985 150hp Black Max idles hot

Thanks for the input Chris. Previous owner said the impeller was changed in Sept 2008 so it is very new. Most puzzling thing is it runs cool at higher speeds. It only gets hot at idle or very slow speeds. Was that the symptom you had?