overheating 1988 150 mercury

[crawfw]

I have a overheating problem and have done all the normal things that I can think of. Runs cool at full throttle, but at no wake speeds it does not. Changed impellers 2 or three times,had entire pump and housing replaced, blown out cooling system both ways and changed thermostats. I have heard about a possible crack in my exhaust plate but this would require some disassmbly of the motor. Any help would be appreciated. The motor is a 1988 150h.p. XR4 black max. Motor runs good and I mix my own oil 50:1 ratio.

 

[j_martin]

Re: overheating 1988 150 mercury

I have a overheating problem and have done all the normal things that I can think of. Runs cool at full throttle, but at no wake speeds it does not. Changed impellers 2 or three times,had entire pump and housing replaced, blown out cooling system both ways and changed thermostats. I have heard about a possible crack in my exhaust plate but this would require some disassmbly of the motor. Any help would be appreciated. The motor is a 1988 150h.p. XR4 black max. Motor runs good and I mix my own oil 50:1 ratio.

Check the poppet valve on the lower starboard side of the engine. Odds are it has some debris in it holding it open. That would drain the water off the block at idle and overheat it, and wouldn't make any difference at WOT when it's normally standing open anyway.

Other possible faults in it, weak/broken spring, rubber seat cocked in the hole.

Pressure should be 5 or so at idle, go up to 10 - 15 at around 2500, drop a few pounds then continue up as rpms increase.

If you don't have a pressure gauge, get one.

hope it helps
John

 

[crawfw]

Re: overheating 1988 150 mercury

thanks for the input. Looked at poppet valve and everything seems normal. Just wondering where the water goes when it does open because there is the obvious hole on the left where I assumed the water would dump, but there is also a large hole under the spring that it would probably also go. Once water gets through the valve it is not supposed to return to the cooling system anywhere? Just trying to figure the path of the cooling system. Trying to find a repair manual but doubt it shows me the water route.