2002 Explorer temp gauge

[gbfan10]

I replaced the intake on our 2002 4.6 Explorer. Everything went well and been driving it for a few days. After driving it one day for 20 mins, the temp gauge pegged all the way to hot and the truck started going into a limp mode. No coolant was overflowing, and it didn't seem hot.. The heater was putting out normal heat. I shut the truck off and for the next hour+ the gauge was still pegged when I turn the key. I let it sit over night and turn the key on. The gauge now goes up halfway.. THis is after sitting for a day. Once I start the truck the gauge slowly drops all the way to cold, then creeps up normally to the middle range as it should. I do not believe this is a bad head gasket, as the oil and coolant look great and I have never lost any. I am suspecting the cylinder head temp sensor that is under the intake.. I just don't want to pull the intake to get to the sensor if that's not it. Any thoughts?

[61falcon]

could be an air pocket in the cooling system

[Lincolncruiser95]

+1 on the air pocket. Did the intake gasket on my Towncar and had a similar issue. Gotta "burp" the system. Park so your coolant bottle is the highest point (assuming explorers are the same and have no radiator cap). Then run it up to temp a couple of times. Once up to temp rev the engine to create a surge of coolant that will push the air out. You have to do this with the cap off and may make a little mess. You will actually see the air come out and the level in the botttle drop. Usually this works for me. Did the same on my truck with the 4.2 after a new water pump.

More often than not your thermostat is the highest point in the block. If you've got a bubble around it it wont open as it must be immersed to operate properly, hence your overheat

. You may have to pull it and fill the block by pouring coolant down the passage below. Some vehicles also have a bleeder valve one one of the heater hoses also. My Mustang does IIRC.

[gbfan10]

I tried parking it on a car ramp on one side, so the coolant bottle was the highest point, I let it run up to normal temp with the cap off.. When I rev it up, it made no difference to the coolant in the bottle, it stayed the same level and wasn't circulating. I checked the temp of the coolant in the bottle and it was only 92 degrees, I traced it down to the lower radiator and to a crossover pipe that ran along the bottom of the radiator and that wasn't really warm either. Some other temps I checked.

Thermo housing was 174
Upper rad hose was 150
lower rad hose 127
heater core lines 158.

I am sure the thermostat is opening, and I also have good heat in the truck..
I am at a loss..

[Guns R Tools]

Could it be loose wiring by temp sensor or bad sensor.
When hot, it could act up.
Do a wiggle test when it is pegging.

[gbfan10]

I will try that. I may also install an aftermarket coolant gauge, that way I can confirm the gauge is a liar. If the sensor wasn't such a pita to get to, I would have replaced it by now too