Strange Overheat Issue?

I have a 1960 CJ5 with the F-Head that has a strange overheating issue. I mainly use it only to plow snow. The issue I am having is it warms up at a normal rate but continues to climb to 220 sometimes 230 before I catch it during the first 10-15 min of plowing. I’ll then stop and let it idle for a minute or s two and all of a sudden it will come back down in a hurry to 180. Once it does this it works fine for hours after that with no issue. It only seems to do this on initial warm up on a cold motor. I do have a factory heater in this too. I did recently install a new Stant 180 t-stat as the PO never had one in it, and it has been doing this since I put it in. I did run it for a while with radiator so off after installing it. Could it be a faulty T-Stat? Coolant is full and I can shoot an infrared thermometer at the sensor where it screws into the head and get a reading close to what the temp gage says. Any ideas? TIA.

 

I think you answered your own question.

Sounds like it is slow opening until the radiator gets hot. Does the thermostat have a small 'by-pass" hole in it, so it gets warm water to to the sensing capsule? Was it installed in the correct orientation? Does your engine retain the small by-pass hose to the head from the water pump?

Also, an F-head wants a 165ºF thermostat by standard OEM specification, 180º was an option. In extreme cold weather, a 180º unit may not get warm enough to open before the block water passages start boiling. BTDT.

 

nothing more to add

 

+1 on T stat

 

You might also want to be sure the heater circuit is "burped" of any air anytime the coolant has been drained, but if you've been running the Jeep for a while that should not be an issue now.

 

Thank you for quick replies. I figured I was answering my own question but found it hard to believe that a new Stant T-Stat would be faulty. There is no weep hole in it and I have it installed with the spring down. I have been plowing in extreme cold (0 degrees and colder) too. I will get the original 165 and put that in. Thanks again.

 

What they said, it sounds like the thermostat is sticking and when it finally opens it is OK until it cools down completely and sticks again. I think I would try another thermostat the same as you have, it could just be a bad one you got this time, Stant usually is good stuff. Good Luck

 

I'd run a 180, with a 1/8in bypass hole drilled in it.
That 165 won't put out much heat in single digits!

 

If the problem started after you installed the new thermostat make sure all the air is bled out of the coolant system. I had this exact same issue and that was the problem.

 

Those funnel bleeder thingies actually do a decent job.

 

Redneck tech, but it works sometimes for trapped air...
Once the engine is hot and thermostat is open, drive straight up the steepest hill you have and give the engine a good rev. If there is an air bubble in there, it can burp it out.

 

Also to purge air: with radiator topped off, engine running and hot water circulating loosen the temp sending unit to the point it weeps and just begins to leak. Run the throttle up and down until only water is coming out. Tighten sending unit. Clean up any puddle (furry friends and green fluids don't mix).
On some fehicles (jeep 4.0 for example) I've added a bronze "T" above the sender hole and used on part of t fro the sender the other for a petcock. Some engines seem to have more problems than others with air trapment.

 

Or pulling a heater hose can fix it.

I've also found that after it boils over two or three times, it has burped itself....