My 1998 Jeep Cherokee 4.0L randomly overheats on me. Since this is a cooling system related issue, I’ll only mention the parts I’ve replaced on my cooling system.

When I first got it, I replaced the water pump because gasket was leaking, then a few hundred miles down the road I get check gauges, and temp gauge was all the way to 250°F driving down the road it almost instantly turned the lights out and gauge returned to 210°F. As easy as it is to get to the thermostat and how cheap they are, I purchased one on the way home and the next morning when I got to my shop I replaced it. I have a machine that vacuums the system down and sucks the coolant into the system. This tells you that for 1 there’s no air pockets, and for 2 there’s no leaks 100% of the time.

A few more hundred miles down the road check gauges and we’re running 250°F. I immediately pull off the road and can hear the system boiling from inside the truck. Coolant coming from the radiator cap and the over flow was well, overflowing. I had chalked it up to being a defective radiator. The cap did feel a little loose, and yes, I pressure tested the cap and the radiator. They both held pressure, but idk I’m stupid sometimes I guess. That’s how we learn.

So foolish me purchases a radiator and installs that. Same exact issue. The cap does however fit more snug but still leaked, so eh I guess it's a win-lose situation lol. However, as it’s leaking coolant from the cap, I check the temp inside of the truck and notice my ac is on. I get out and BOOM, I notice the darn ac / cooling fan is not engaging! I tested my power and ground from the computer side, and yes, I even jumped the high pressure switch to try to trick the computer into turning on the fan. Swapped my relays, even used my power probe to try to power up the fan with no luck. I also did a head gasket leak test too. I have ordered me a fan and have it sitting right here in from of me. Later tonight I’ll post an update. I hope this helps out somebody in the future. Always triple-check your diagnosis or you’ll wind up wasting money on parts you do not need. Like me..