01 TJ Temperature Problems

[txapacheguy]

Driving down the highway, the temperature gauge goes from normal (just past 210) to the beginning of the redline almost instantly...(probably 240ish). This problem just appeared today driving from Colorado to Texas.

I have several theories, but would like to know if anyone has had the same issue... The first few times it happened, I shut the engine off and coasted for a minute or so, and by the time I turned the key back on, the temp was back to normal. (red flag goes up here) I finally worked up the nerve to continue driving normally when the problem occurred. The issue went away by itself within a minute or so when I continued driving.

Background on my rig as follows: 2001 TJ with 4.0, manual trans, A/C, 90,000 miles. Relatively new water pump, hoses, thermostat, and properly mixed coolant serviced to the appropriate level. (Before anyone asks, the radiator and A/C condensers are also clean and free of obstructions)

I first suspected the fan clutch, which will get replaced tomorrow or the next day(have new one already). I also suspect that either the thermostat may be sticking in the closed position, but I would guess that the almost instantaneous rise, and subsequent drop in indicated temperature would rule this out... The coolant temperature sensor is also suspect, as it has never been replaced, but I have no idea what symptoms one of these will display when it begins to fail. I have not had the "codes" checked, but plan to do so if the clutch does not solve the problem, or if the problem does not magically solve itself. Thanks in advance for any insight to this problem...

[jjkather]

I've had the same problem in hte past on a 2.5 equiped jeep. Mine was the temp sensor. Not that this is yoru problem, but it would seem that if the problem came up and then corrected itself while continuing to drive, that 1 of 2 things is happeneing. either the sensor is messing up, or you have air pockets from low coolant level. if you are sure the coolant level is good, i owuld opt fo the sensor, usually a fast easy fix and a cheap part from a local auto parts store. just pull the wire/plug off the old sensor, unscrew it(you will lose a litle fluid here, just have the new one ready), quickly insert the new one, screw it in and reconnect the wire. Just my 2 cnets, hope it helps

[socalkenny]

I had this exact same experience a couple of years ago while driving cross country. Are you getting any secondary indications to lead to you to believe that you are actually running hot? If so here is my experience for what it's worth. I had a clogged heater core, and that was evident since the heater wouldn't make any heat at all and it had been that way for at least a year. I tried back flushing and it just wouldn't help much. I ended up replacing the radiator and heater core. Now I flush my system once a year and have had no other problems.

[lys327]

i have had this problem a few times and 6 out of 10 times it was the that the system had air pockets in them. just make sure that the thermostat is in properly< i made that mistake once> and the biggest is the bleeding of air pockets. squeeze the in and out hoses and see if you get any gurgelling, indicating that there is air in the system. this is the cheapest thing you can do.

[lys327]

you might also want to check the pressure/fill cap. it has a pressure rating. that device serves multiple purpopses. it lets air in to keep pressure. it bleeds air of if the pressure is too high. and it also pressurizes the system.

[txapacheguy]

Thanks for the feedback and ideas. The latest story is as follows... I replaced the fan clutch the morning after I posted this thread, and drove the jeep for almost four hours in 100 degree heat with no problems. Today, I drove it from Texas to Alabama without a hint of overheating... I do not know if I fixed "the" problem, but I certainly fixed "a" problem. The engine seems to run a few degrees cooler at highway speeds with the new fan clutch anyway. As with all things Jeep, I am sure this saga is not over yet, but thanks for the help so far!!!