Gremlin in the radiator?

[Dan Carey]

2004 TJ Rubicon. This Jeep has developed a strange problem in the cooling system. I was in town at a stop light on probably a 5 degree grade facing up hill. The light turned green, I got on it hard for about 300 yards, the temp went to about 230 when I saw it I got off the gas. The temp fell to 200 very fast. The same day, I replaced the thermostat. The next day I did the same thing and sure as H it did the same thing as before. It has a new Radiator. I have done the same test on it several times with no temperature rise at all. so, it is hard to pinpoint the problem. This something new. What do you think?

 

[hear]

My first guess would be that you need to burp the cooling system.

 

[CharlesHS]

When you replaced the thermostat; did the thermostat come with a bleeder hole or did you drill a 1/8" hole in the flat section of the thermostat ensuring the hole was at the 12 o'clock position. This bleeder hole will assist in the removal of air from the cooling system.
You should also check the resistance of the thermostatic clutch when the engine is cold and when the engine is warmed up.

 

[Dan Carey]

The thermostat I removed looked to be the original Mopar with a hole and ball in the top. The aftermarket I put in didn't. Thanks