Cooling system burping problems

[MrWampus]

I just replaced my thermostat because the old one was very leaky and the car ran cold all the time. I installed a new one, wrong orientation at first as I discovered after not being able to get the system to cycle properly. I switched the thermostat to the correct position today, (valved side attached to the bottom hose from the radiator) refilled the system following the instructions in my IAP shop manual (fill radiator, remove bleed plug at T and fill, remove throttle hose heater and fill until it overflows, fill overflow tank). The interesting part is that the car has been still and cold for 3 days but when I turned the key for the first time today the temp gage in the dash immediately jumped to about 225 (midway between 190 and 260). I know that was wrong, the car was stone cold. I let it run for a while and the gage slowly climbed from there to the start of the red zone. I got nervous and shut it off. I checked all the hoses and all three hoses attached to the thermostat were hot so I'm getting full circulation, but the fan never came on. I don't know if it just never reached the temp for the fan to click on or if I still have a bubble somewhere or what, but I don't trust the dash gage since it started out from dead cold reading about 225. Do I just let it run and ignore the gage to see if the fan finally cycles? (Not in my comfort zone) The gage and everything seemed to be working fine before I started, it just always ran cold. It would reach the 190 mark in heavy traffic and the fan would cycle on at the appropriate temp. Ideas?

[RRoller123]

Maybe start by checking the connections to the 2 temp sensors in the top of the head between the spark plugs. If you just changed the T-Stat, it seems unlikely that the sensor(s) would choose that particular moment to fail.

[MrWampus]

Maybe start by checking the connections to the 2 temp sensors in the top of the head between the spark plugs. If you just changed the T-Stat, it seems unlikely that the sensor(s) would choose that particular moment to fail.

Success! Yes, that was the problem. When I last finished the job, I had spilled a good bit of coolant on the engine and I lightly sprayed it with water to clean. I apparently disturbed one or both of the connections. I reseated both and the gage went to normal. I then allowed the car to warm up to running temp and the fan came on at about 195. I let it cycle twice and it seems right. Now for a brief road test near home to confirm. Thanks for the hint.

[RRoller123]

Blowing out around the plugs and sensors with compressed air does the trick. (wear glasses) I find it nearly impossible not to spill coolant on the top of the engine when doing the TPH fill.