CSWTTU97

Less than 3000 miles ago rebuild engine, replaced radiator etc at Thunderbolt in Houston. Now engine runs between normal (12 o’clock position) and red hot (3/4 position) while at hwy speed. Ambient temp 82, no load, stock grill, no winch or any other item blocking front air flow. Fan comes on almost immediately after start up and stays on. Temps run slightly warmer that normal when at 50 mph or below. No codes, no warning lights. Any suggestions as to why this is occurring?

Jay2013jk

Welcome to JKF. Good friendly knowledgeable group here. 1st thought if you have a Jscan hook up and watch the actual temps on the Jscan. If you need Jscan: .JScan ? OBD JScan ? Mobile Jeep, Chrysler, Dodge Diagnostic Tool The also have a good facebook page. 3.6l engines do run around around 200+ as most newday engines are designed that way for emissions and efficiency. 2nd and 3rd thoughts.. Temp sensor issue; and the possibility of air in the system so additional "burping" might be in order; multiple yuoutube videos on this process.

RwH

Like said above, burp the system again. and then do it again. Possibly a "slow to open" thermostat could be the issue as well. I've learned to not use cheap thermostats in this engine, only the MOPAR brand. I absolutely hate the design of this jeeps cooling system.

Sixty4x4

Based on the fan coming on at startup I would determine the sensor is giving false readings as the water would be either cold or at the most warm. When it gets to that "level" you should pull over somewhere quiet (if there is a place left in the world that is) and turn off the engine to see if it is boiling but do not release the rad cap - just listen.

casamtb

Id second the mopar thermostat as a try. Mine was doing the same thing and running warm at highway speeds with an aftermarket thermo. At over 70 the needle would start to creep. Between half and 3/4 and from the readings i was getting with blue driver the needle moves at 228 and is 240 at 3/4. I was running high 220s and 230s if i ran above 70mph. It would come back down but slowly. I read a bunch online and replaced with a mopar recently and it solved the issue. Now running 75-80 im seeing 217-223. The mopar spring assembly is much more substantial than the aftermarket that was in it and i have to believe the spring was misaligned and it wasnt opening cleanly and getting proper flow. Like i said mooar thermo solved the problem.