overheating 1990 yamaha 85

[popeye]

thanks,, motor over heats, i have replaced the impeller therm, I pull the cover and see scale and shells,, now nothing i crank the motor and water runs great out of top, I replace therm cover and good for a 10 min then again.

I have run the motor for a short time without thermstat, mechanic suggested a little murtic acid, flush well..Any thoughts

Thanks

[Hamfisted]

Find a new mechanic.

Aluminum and muriatic acid don't play well together. Get some Salt Away or Salt Terminator and spray it in there instead. Did you inspect the pressure relief valve as well? If it gets stuck open you'll lose your cooling water before it can fill the powerhead. Its located behind that cover at the rear base of the powerhead where that 3/4" hose connects. There's two 10mm screws to remove and the cover pops off. Inspect the seal area for debris. Inspect under the round seal for mineral buildup and scales. Never run the motor without thermostats, they are required to provide adequate restriction to fill the powerhead completely, thus avoiding hot spots on the top two cylinders. Use new gaskets on the thermostat covers too. Always use a good 3/8" torque wrench and torque to specs all bolts.

If you don't already have one you can go to www.Yamahapubs.com and order a factory service manual for your motor and they'll mail it to your door.


Mike......... Miami, FL

[popeye]

thanks Mike tomorrow I will check it out,