I just picked up a 2000 XJ yesterday that I won off of Ebay. It's in good condition for 110,000 miles but needs a little TLC. Issue #1 to take care of is the coolant system...

The problem: The coolant temp gauge reads very low. It sits at the 100° when driving and goes up barely one tick when idling for awhile. The heat seems to be working well though so I think it may just be a gauge issue. When I shut the motor off when I got home, a little bit of fluid seeped out through the radiator cap. Any ideas on how to proceed???

In addition the the gauge issue, it seems like my XJ may have had the Dexcool mud issue. The current coolant is the typical green but the overflow bottle and the neck of the radiator are stained with the rusty brown color.

I'm definitely planning on replacing the radiator cap, water pump, t-stat, t-stat housing, & overflow bottle ASAP. They look original and the bottle looks like it is leaking. The radiator hoses and serpentine belt look like they have been replaced recently. The fan clutch seems OK - I can manually spin the fan about 1/2 a turn.

I'm looking forward to the suggestions. I plan on getting everything up to stock standards and then the fun can begin!!!

 

change the temp sendor its at the back of your block, it bolts in and out and then a plug goes into it, could just be a faulty sensor

 

2000 is in the front by the t stat. I would replace that first then do the cap.

 

The fan should kick in if you let it idle for a few minutes, if not the coolant sensor is probably bad. When they fail they read low.
The brown coolant results from the cooling system being neglected. Dexcool, Prestone any make any model, and even the recommended HOAT (G-05) are all OAT based coolants and will cause the same brown mud that GM's dexcool has unfairly gotten blamed for. Air,overheat,mixing tap water,allowing overfill jug to get low, not routinely changing coolant or leaks will cause disaster. If your radiator cap is leaking like you said, it is also sucking in air.

 

So on the later XJ's did Jeep combine the temp gauge sender and the FI temp sensor? I was searching some posts and saw mention of the temp gauge sender at the back of the head but couldn't find it on my vehicle. The brass sensor in the t-stat housing is what I need to replace?

I haven't seen the electric fan run yet but it has been very cold here so I wasn't too worried about that. If the electric fan reads off of the same temp sensor as the gauge then I doubt it would turn on since it thinks the motor is cold. I definitely plan on flushing the coolant system when I replace the water pump etc.

 

'97 up have 1 coolant temp sensor and it's in the t-stat cover. Also, on '97 up the ECU signals the temp gauge based upon the signal from the CTS. This time of year, we won't here the efan for several months (unless the compressor is engaged).