New 3 row radiator; new 195 therm.;new water pump; new fan clutch. All other components seem to be working correctly. The jeep is a 99 4.0 automatic and can sit at idle all day in the summer sun without breaking 195 but just as soon as I take it down the highway the temperature goes up to about 220 but no higher. Anyone know why the temp might be going up on highway and not at idle?

 

Do you know the gauge to be accurate?

 

I changed out all of those same componants in my 91 XJ. Mine would do the same thing. I swapped the T-stat for a 180 degree. Now, my temp is 180-185 on the highway and it flirts right around 210 when crawling along wheeling. Pretty much anything outside the red on the gauge your Jeep can run at all day long with no worries. I am like you, though. I wanted it to run about 10-15 degrees cooler at idle and under load and the T-stat swap did the trick.

 

I second verifying the gauge. Got access to a digital scan tool?.....plug it into the ALDL port under the dash.

 

Not sure about the guage will check it tomm. It stays under the 210 mark at idle and while cruising on trails or intown traffic and doesnt go any higher until at highway speeds.