OK so i just started having this problem today (or at least that ive noticed). when im at a light or something the temp gauge will start to rise above normal and slowly keep rising until i start moving, but once im moving it drops right back down to just below half. any ideas on this? my first guess is either the thermostat or something to do with the fan? im leaning more towards the fan because when im moving and getting air through the grill its fine.
also i noticed that when i shut the car off and turn just the key on the gauge was still rising. i know that it cant get hotter with the engine off so what would cause that? something with the coolant temp sensor? it just doesn't make sense why the gauge would continue to go up with the engine off!
any help on this matter would be greatly appreciated.

 

As to the first question, we will need more information to answer it. How hot is it getting? Over 210? In the red? Is the auxiliary fan coming on? Have you verified visually that it isn't? No leaks or recent work on the cooling system?

The second question is simple physics, when water doesn't move when it is in contact with heat, it WILL get hotter. This is the reason you remove something from a hot burner on your stove so that it doesn't burn after you turn it off. This is probably what your sending unit is telling you.

 

could be radiator.. stuck thermostat. mixture of things

 

when i stop and it starts rising from just under the 210 mark, it will rise to the next line on the gauge (about 3/4 the way up just before the red) and im guessing it will keep rising but i havnt let it get that far.

i couldnt say for sure about the aux fan, but as far as ive seen it only comes on when the AC is on.

the rig does have a leaky heater core but ive been really consistant on keeping the fluid level where it should be (resevior half full when cold)

 

hey wouldnt a fan clutch cause pretty much exactly this? how do i go about testing it? and how complex is an electric fan conversion? any writeups on this?

 

Simple test...... Open the hood, start the vehicle, turn on the A/C and see if the aux fan comes on.
If it does then the fan is not the issue...
If it does not, then the fan IS the issue. I picked up a few at the pick-n-pull for $50. (cant trust junkyard electrical parts)
Could be a temp switch, but I am sure the temp gauge and fan run off the signal from the same switch, so that is most likely not the problem.
I think the temp for the aux fan to come on is 220*, so it does get higher than I like to see it, but that is the way it is...
You can also turn on the A/C while sitting at the light when it gets hot and see if the temp comes down.

Electric fan conversions are not very difficult at all. Both of my other Off-road vehicles have been converted and work perfectly. You can also set the temp that you want them to come on and therefore keep the temp down lower.

 

what about the fluid level in the actual radiator?

 

not really at idle

 

2 different switches. the gauge switch is on the back of the head. the computer switch is on the thermostat housing.

 

Worst case is water pump. Ive seen the impellers completey gone!

 

mine is doing the exact same thing as this..very strange as mine does not do it all the time..the fan is ok and ive recently changed the radiator and thermostat plus housing..i was guessing it was the temp sensor sender but am unsure a the moment..
were you able to find out what was causing the problem?

 

The #1 cause of "temp creep" ONLY at IDLE (but not when vehicle is moving) is the fan clutch.

Often overlooked, inexpensive, and easy to replace it. I'd recommend you do so.

 

Sounds like fan clutch.

 

I recently had a similar problem with my 2000. After trying to fix the problem on the cheap and still overheating, I decided to replace the entire cooling system...it ended up being the water pump (the impeller was completely rusted away).

To test the fan clutch, I've heard that you should spin the fan by hand. It should not make more than one revolution. Keep in mind, I have no idea how accurate a test this is and decided to replace everything on mine instead of replacing components one at a time.

With regard to the electric fan conversion: http://go.jeep-xj.info/HowtoElectricFan.htm. Also Dirtbound offers a conversion that replaces the mech. fan and aux fan with 3, 10" electric fans. It's a bit pricey and I have no idea how well it works but maybe it would be something you're interested in.

 

so would you recommend replacing the electric fan?