Well, i'm a noob I posted this over on the grand cherokee forum but my question is
A few weeks ago my wife woke up to her 98 cherokee classic 4.0 with a puddle of radiator fluid underneath. She didn't run it low on fluid judging by the puddle and the ammount still in the radiator it was just a slow leak that finally split the hose. I replaced the hose and while i was at it I flushed the radiator. I saw that the radiator fluid was the orange fluid like you see in a GM vehicle and replaced it with the same. It ran fine for about a week and then she called me and told me that her jeep had overheated (check gauges light, temp was at 250) so she pulled over a few minutes to let it cool down. she has a long commute so I let her drive my truck from then on and I've been driving the jeep and just nervously watching the guage. Well today coming down the highway, watching the gauge every 45 seconds or so because the temp out side was 100, and I had the A/C on full blast so I was keeping a close eye. Well all of a sudden the check gauges light came on and the temp instantly went from 210 to 250. I instantly cut the heater on full blast and looked for a place to pull over. not 15 seconds later the light went off and the temp went back to 210 like nothing ever happened. Should I send it to a mechanic? does anyone know whats wrong? maybe a bad temp sensor or gauge?

Sorry for posting on both forums, I hate it when ppl do that

 

Sounds like a faulty temp sensor to me.

 

You may want to change the thermostat. Also is the electric fan coming on?

 

Instantanious jumps of 40+ degrees, then jumping back down? Really sounds like a bad sensor to me.

 

My 99 was doing the same thing until I changed the radiator...Before changing the radiator I changed the water pump, thermostat, temp. sensor and none of that helped... Why the radiator, I don't know.

 

flush the block also... that did wonders for me!