Thermostat/temperature question!

[DumbBass]

I just replace the themostat on my '89 Johnson 60HP. With the original thermostat in place, the motor never seemed to warm up. I could leave my hand on the head with out any problem. The new thermostat warms motor considerable hotter. I measured the temp at the top of the head @140*, which is what the factory manual specifes. The temp at the bottom cylinder measure 160*-165*. Is this normal? Anything to check? I'll replace impeller next but wanted some feedback on the temperature!

 

[David Ayers]

Re: Thermostat/temperature question!

I,m not an outbord mechanic but according to the Clymer shop manual on 91-94's a 163deg. thermomelt stik should not melt and 155deg. max using a pyrometer.Hope that helped a little.

 

[Jack Shellac]

Re: Thermostat/temperature question!

It could be that your old thermostat was stuck open and the motor never did actually reach operating temperature. The head should feel hot, but not so hot that you can't put your hand on it. BTW, I like your name-shows you have a sense of humor.

 

[DumbBass]

Re: Thermostat/temperature question!

Papa Bear, I have a factory service manual. The procedure for measuring temp is: run motor @ 3000RPM for 5 minute, reduce to 900RPM, measure temp at top of head. Temp should be 140* plus/minus 15*. Then run motor @ 5000RPM, measure temp, should not exceed 160*. I'm using a RAdio Shack IR sensor. So far, I have only run motor on muffs @ idle. I don't know if this could result in higher temp readings.<br />Jack Shellac, I suspect you are correct about the old thermostat being stuck open. I've read a number of posts about this engine being finicky about operating temp. I could touch the head with my hand and it was only slighty warm. Now, I can touch the head but it is MUCH warmer. My main concern is why the lower cylinders feel and measure so much warmer than the top. OH yeah, you have to have a sense of humor when dealing with my level of mechanical ability! (C:

 

[G DANE]

Re: Thermostat/temperature question!

Dumbass<br />When did you last time service your water pump ?<br /><br />When impeller gets older water flow will slow down and buttom cylinder gets "used" cooling water causing higher tempareture as water enters through exhaust jack and from there to upper cylinder on the big twins like your.

 

[seahorse5]

Re: Thermostat/temperature question!

Running the motor on a hose will not give an accurate test, but it does show that your thermostat is operating correctly.<br /><br />If you are checking the lower cylinder's temp on the head, you are seeing the results from water that has already passed thru the thermostat at 140 degrees, and is still picking up heat from the other cylinders on its way out the exhaust. That is normal. If you check the cylinder block temperature of the lower cylinder, it will be closer to the 140 reading.

 

[DumbBass]

Re: Thermostat/temperature question!

G Dane, I've owned the motor for 1 1/2 years. I have not changed the impeller yet so it is time to do this. I was hoping this was the case.<br />Seahorse, I will check cylinder temp instead of head to confirm your recommendation.<br />Thanks for all of the good information. Hopefully the new impeller will correct the temp discrepancy.