Trying to work out this issue while I'm stuck at work. Last weekend my '99 Cherokee XJ 4.0L - started to run hot - "check gauges" dash light came on. I immediately pulled over, and I noticed that there was no coolant in the reservoir. Filled it up and went on my way without issue. This is odd because I checked, and added some the week before. I usually check my fluids on a regular basis. Today the "check gauges" light came on again because it was running hot again. Pulled over again ready to fill up the reservoir, but this time it was full!??? Drove part of the way to work (just a few minutes) with the heat blasting to keep the engine temp down, but then the rest of the way to work I turned off the heat and everything seemed fine. Even while sitting at lights a couple times for over a minute or more, the temp gauge didn't climb.
My first assumption is that the thermostat is not working, or only working when it wants to. The fan seemed to be working over time this morning too. Could this be a water pump issue?
Any insights so I can pick up what I need this afternoon? I know the parts are not very expensive, but I can't replacing both this week.
Thanks in advance for your help.