Coolant temp sensor and coolant problems

[drcomanche]

So recently, I just got the truck back to running condition. I started it and just did some general checks(this coming after taking apart pretty much everything but the block and head and replacing most) to make sure it was all functioning. I replaced pretty much everything in the cooling system with the exception of the pump, t stat, and housing because they had only seen 500 miles of use. So here's the symptoms as they occurred. 

 

Checked the coolant level from cap after cooldown and it erupted out of the radiator fill when the cap came off. I was just checking to see if it needed more. Coolant was cold.

 

Checked again the next day while fully cold with cap off to check level. It slowly filled over the course of 2 minutes until it started to pour out of the fill. Coolant was, again, cold.

 

Capped the radiator and started it again, expecting that maybe it was caused by air in the system. Ran for 3 minutes, noticed that oil was seeping from the valve cover, went to shut it down and saw that my temp gauge was beyond even numbers, well beyond the red. Radiator was cold to touch. No fans came on with the sensor. 

 

Panicked about potentially warping the head. Decided to leave it till tomorrow.

 

Decided to check the gauge reading at complete cold, no engine start. It was reading at 190 in acc on position. Started the truck and observed the temp gauge, it started rising immediately. 

 

And thats as far as I've made it. 4.0 I6 engine. Not sure if these correlate but it does have me concerned. I did change out my wiring harness over winter, but its still an ho harness. The jeep has an all electric fan setup run to a single out sensor on the t stat housing, meaning no connection to the harness anymore. I also changed the temp sensor on the head, which had a different plug style, but was still one wire. Did the sensors change their output over the years and maybe it's a different resistance reading from start? 

[MiNi Beast]

Was lower rad hose hot? Is the fluid circulating? Pump on backwards? You have a open system? 

[drcomanche]

On 9/16/2020 at 10:23 AM, MiNi Beast said:

Was lower rad hose hot? Is the fluid circulating? Pump on backwards? You have a open system? 

Lower hose was cold

 

Not sure. Something is moving or else it wouldn't overflow the rad

 

Nope

 

Yes, its an open system

 

I did pull it all apart since I was taking off the balancer and as soon as I removed that thermostat housing it let loose a bunch of coolant. Pump seemed fine, housing was fine, t stat was fine(but I'm replacing it anyway). Another thing I noticed after playing with the sensor, when unplugged, the gauge drops back to normal. When plugged in but the the key in acc position, it starts climbing, even though the engine isn't started. I think, initially, my t stat was seized or blocking air in. I'm going to fill the coolant a different way this time that shouldn't leave any room.