1987 150 MERC overheating under pressure

[tonyiii]

I have 1987 150 Black Max Merc that over heats only under pressure. I have checked all of the incoming cooling areas. I have removed the leg and put a hose directly to the cooling tube and opened the thernmostats. The water come out great. I also installed a new impeller kit. I put the boat in the water and it pumps fine the tell tail is comeing out great. At idlt and up to 1200 RPM's it runs cool as soon as I go beyond 1500 RPM's it heats right up and go's past 180o before i pull the rpm's back down and as soon as I do that the tempo falls right back down. I have been told that I must have a restriction in the exhaust and I should remove the power head from the lower housing and check for salt build up. I was wondering if anyone elses had any ideas. I have not been able to get out yet this year and my seasoin is almost over I'll try anything.<br /><br />Thanks Tony

 

[grandx]

Re: 1987 150 MERC overheating under pressure

Tony welcome aboard. Does your engine have a warning horn? My horn sounds at 240 F. Thermostat opens at +/- 145 F. Are you running it on the water when this happens, and what does the temp read when running at say 3000 or 5000 rpm? Is your gage accurate? many are not. Test your warning horn by grounding the tan/blue wire. Many of these mercs run warm in differing conditions, mine don't like mid rpms, but are ok wide open and at idle. May be a problem with the poppit valve, this valve takes over water delivery at a specific rmp, not sure what that is for your engine. Get a manual for your engine to get exact info, search the board for hot/warm mercs and you may find a similar issue with a similar engine.

 

[BF]

Re: 1987 150 MERC overheating under pressure

are you getting good water flow at higher rpm's? Is there lots of water coming out the rectangular exhaust/water outlets at the back? Maybe your water pump is failing to pump at higher rpms. There were a couple of threads about this here within the last couple weeks.<br /><br />Brent

 

[RVAHA]

Re: 1987 150 MERC overheating under pressure

Tony, you may check out this thread that I've got open. http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=008258 <br /><br />The poppit valve was the wrong type and would not open. I'm sure if it was defective or clogged it may act the same way.<br /><br />Rick

 

[jim dozier]

Re: 1987 150 MERC overheating under pressure

Go to the Suzuki/Yamaha forum and search for member # 20179 for a thorough discussion of a similar problem on another brand of OB<br />"Topic: 85hp suzuki still overheating"<br />by fish4970