1988 yamaha 150prov overheating issues

[Red612..]

Ok, I have been reading this form for a while now and gotten alot of troubleshooting Info. But I still have not corrected the issue. I have changed with brand new parts POPPET VALVE ASSEMBLY, T-STAT`S, Pulled the heads and cleaned all Calcium out of the passages, Thermo switch assembly both sides, I forgot to add that it only over heats at about 4,000RPM-WOT. I also changed the WATER PUMP IMPELLER not the whole kit though and the impeller is a aftermarket brand not Yamaha. I had someone tell me to put a whole kit in Yamaha brand???? and it will pump water better.

Whats weird is the Temp gauge is not showing its overheating so maybe the gauge is bad. I bought a new one but have not installed yet. The way I do know its overheating is the buzzer goes off and RPM`S drop to a idle.

Any info would be great i am kind of banging my head on this one.

[99yam40]

1st thing I would do would be test the overheat alarm and see if that sets off and indicator on your gauge.

low oil will also set of an alarm and set RPM limit

Yes it is best to replace cup and wear plate along with the impeller.
Plastic housing needs replacing from time to time also if there is any sign of damage

[Red612..]

Thanks Yam40, If it was the oil wouldnt the indicator on the Tach light up with the no oil symbol? I am pretty sure its getting oil cause when this first started happening I checked the reservoir under the cowl and it was full.

I think I might go ahead and replace the whole water pump assembly and see what it does. When I did change it before the old one didnt look that bad and the problem was still happening.

Thanks

[99yam40]

Whats weird is the Temp gauge is not showing its overheating so maybe the gauge is bad. I bought a new one but have not installed yet. The way I do know its overheating is the buzzer goes off and RPM`S drop to a idle.

Since the gauge is not indicating what the alarm is, test to see if the oil or overheat indicates when you set them off manually.
If they do not then find out why and fix it. that will make finding what alarm is coming in a lot easier

[madharchod]

i would be looking at the thermostat first before i would go and replace the impeller a sometimes what happens is these old motors start giving false alarm when the thermostat is on its way out