Is my Mercury 150 Toast? Please Help!!!

Hi all, I'm a new user here and new to the outboard seen, I've always had I/O.
Bought this old Glassmaster with a 1985 Mercury Black Max 150 on it for a general fishing boat, took it out today and ran it for a good 2 hours with out a problem, although, when I purchased the boat, the owner explained that the impeller was getting week and he gave me a new one. He stated that if you let it warm up slow, it would start spitting water with the impeller that was in it. Well, I did that, and low and behold it started spitting at a decent rate. Like I was saying, 2 hours later, we started loosing power and the engine started smelling hot, smoke from residue on the engine, oil and such, no buzzer went off, no indication it wasn't cooling. Now, the only way to start the motor is to jump the solenoid with a screw driver, and it it'll run, but not long before getting hot. Had to get a 7 mile tow in, not good...........
The major question for me here is, what compression should I have on the cylinders while cold? Can't start it for the obvious,( trying to see if she smoked a head gasket or worse, cracked the head). Also, what's the deal with the no start from the key? Is there a switch that went bad or did the solonoid overheat and burn up when the motor overheated? I am ASE Master Auto Tech so I'm not stupid, but how hard are these things to put an impleller in and change a head gasket? I have never fmessed with one. Does anyone have any specs? Where do I begin?? Or, do I take this motor to the marina and pay a boat load to be fixed???? From what I've heard, this was a pretty reliable motor. Thanks all. HHHHHEEEEELLLLLLPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP!!!!!!!!!!!!

Re: Is my Mercury 150 Toast? Please Help!!!

the impeller is probably the easiest thing to do on an outboard, try doing that first, compression numbers don't mean as much as the difference between each cylinder, I think it's 10 % difference but no more, something like that, hope this helps, J

Re: Is my Mercury 150 Toast? Please Help!!!

A weak impeller is like a leaky water pump in a car. If you drive it like that, and go way out in the desert (or ocean), Murphey's law dictates that it will break. Good thing you had a marine radio with you.

The overheat sensor can easily fail. It's just a klixon thingie clamped to an aluminum head, with the clamp providing the ground. Basically a failure waiting to happen.

Anyway, back to your question. That engine has about a 2 million BTU per hour fire going on in it at WOT. If the cooling system fails for whatever reason, and you drive it, you hurt it fer sure.

You know, (bein' the master mechanic that you are) pistons fail, rings lose their tension, gaskets blow, and so forth.

hope it helps
John

Re: Is my Mercury 150 Toast? Please Help!!!

ok I'll say it: why did you go 2 hours out when you knew you had a failed/failing impeller? it doesn't make sense that the impeller would work better after 'warming up'.

Anyway, I would replace the impeller first.. it only takes a half hour, then check the compression cold. if you have a cylinder way under the others then you have trouble.

Re: Is my Mercury 150 Toast? Please Help!!!

Thanks guys, your help was welcomed with open arms. As for going out with a failing impeller, yep, that was stupid on my behalf and I should have asked a few more questions about an outboard motor before doing so, and yep, I found that stupid little overheat sensor, what genius thought of that p.o.s?

Well, I decided to check compression, and wow, problem for sure, then decided to pull heads off, yep, overheat and nuclear meltdown, both center pistons melted and the other 4 have scored walls worse than I have ever seen. So, looks like a complete overhaul at the marina or a new motor, I'm opting towards just selling the complete package and getting a new boat with an inboard and a v/8, or more or less, something I know how to work on a little easier. Figure the trailer and everything else is worth a small down payment for something else. Thanks again!!!!!!!!!