thermostat change temperature variation

I changed my t-stat today. it is a 92 degree one. now I have a strange temperature struggle. it goes to near 100 degrees and drops to about 70 degrees. up down up down without an end...what could this be? outside temperature is about 30 F

1. Were you having any symptoms or was your cooling system working properly when you changed the thermostat?

2. You mean 192 degree stat, correct? What is the brand?

3. If you weren't having this symptom before you changed the thermostat, (were you??) you likely have a bad thermostat right out of the box. It happens; there are plenty of inferior thermostat manufacturers. Can you get a hold of a genuine Mopar 195 degree thermostat?

here is a vid standig still. the temperature goes up and falls down this never stops??!!?? :huh:

https://vid.me/l7nE

birchlakeXJ said:

1. Were you having any symptoms or was your cooling system working properly when you changed the thermostat?

2. You mean 192 degree stat, correct? What is the brand?

3. If you weren't having symptoms before you changed the thermostat, you likely have a bad thermostat right out of the box. It happens; there are plenty of inferior thermostat manufacturers. Can you get a hold of a genuine Mopar 195 degree thermostat?

Click to expand...

195 degree you are right. I will check the brand tomorrow. I ordered it at rockauto with some other parts.

Also, did you try "burping" the cooling system? Did you drain the radiator when you changed the thermostat. It is possible that you may have air trapped in the cooling system after the repair. Quite common on the 87-90. SEARCH and you'll find the best way to burp the system.

What year/engine do you have? Always best to post that in every thread you start, as there are significant differences throughout the years.

birchlakeXJ said:

Also, did you try "burping" the cooling system? Did you drain the radiator when you changed the thermostat. It is possible that you may have air trapped in the cooling system after the repair. Quite common on the 87-90. SEARCH and you'll find the best way to burp the system.

What year/engine do you have? Always best to post that in every thread you start, as there are significant differences throughout the years.

Click to expand...

1990 renix. what is the best way to get the air out?

courtesy of lunghd; Jeeps Unlimited.....
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Burping trapped air from the head of a 4.0L in-line six cylinder is an easy way to burn your hands or get scalded when ya remove the temperature gauge sender on the head of a hot engine. If you're into pain, or just absolutely just hafta vent trapped air from the motor this way, PLEASE LET THE ENGINE COOL DOWN FIRST!!!

Please be assured that if ya drain out, or lose coolant below the head that air has gotten trapped in the system. Closed systems are especially sensitive to this and seem to have a hard time purging trapped air. Here's how you get rid of that air.

Park the nose of your rig downhill so that the engine is visibly tilted nose down so any air pockets will flow to the back of the head where the computer's temp sensor is. (This is NOT the sender for the electric fan. On factory closed cooling systems, that is in the radiator tank on the driver side below/beside air box.)
DO NOT DO THIS ON A HOT ENGINE! Pressure in hot/warm engine can blow out scalding hot coolant!
With engine off, remove the temperature sender's lead and loosen sender until coolant begins to flow out and no more air comes out. Keep an eye on the coolant bottle level.
Tighten sender back up and reattach the leads.
Top off coolant bottle with 50/50 antifreeze/water mix.
Remember! Do this with the engine COOLED DOWN!

Probably air, but if it isn't, the wrong gasket for the thermostat can do this. A plugged heater valve can also do this. A system with a leak an also cause this, it can suck air through the leak during a cool down cycle. Check your surge tank for cracks, make sure the surge tank cap isn't stuck open. A partially plugged radiator can also cause this.

I've had my Renix do this for various reasons, it would cycle cool-warm, cool-warm but it would eventually overheat and spew.

OK when the sender is out and the motor cold and not running, where do I put the fluid in?

I have to put it in higher than the sensor hole to get it up to this point, right? but there are no other connections I can use to fill it up

OK when the sender is out and the motor cold and not running, where do I put the fluid in?

I have to put it in higher than the sensor hole to get it up to this point, right? but there are no other connections I can use to fill it up

...nose downhill I read, too. That makes sense because of the air going up to the sender hole