1986 Mercury 150hp BlackMax overheating??

[alanR1]

I helped a friend change out his impeller on his 150 because he said it was peeing intermitently and overheating. Evidently the past two or three trips out the alarm has gone off and it is loosing power. He said the pee hole in the back wasn't peeing as much as it should. He replaced both thermoststs and blew compressed air through all of the water lines. And we like I said canged the impeller. We started it and he said that it still wasn't peeing enough. Any suggestions. Thanks

 

[12Footer]

Re: 1986 Mercury 150hp BlackMax overheating??

He may have a leak in the exaust manifold, or a restirction in it.<br />Try a compression trest first tho, because runniong it longer than 20 seconds in alarm, and at minimum, he has some scoring of the cylinders, and probably blown exaust manifold/ head gasket.<br />If he continued to ooperate the boat in alarm, it may be too late for him.

 

[AndyL]

Re: 1986 Mercury 150hp BlackMax overheating??

Check the poppet valve also, as if that is not sealing you will be losing water pressure through it. Normally this is more apparent at low to idling speeds when the pump is struggling due to low rpm.