Carlo Pelandini

I know this subject has been covered a million times, but I seem to have a new twist that is driving me nuts. My 2000 Cherokee Sport randomly shoots coolant out the overflow container. I have taken it four-wheeling for consecutive days with no problems what-so-ever, with it running at the 210 mark all day long. Then my grandson is sitting in the drive-thru at a fast-food place, and it shoots coolant all over the driveway, and the temp is still at 210. Then it will be fine again for many days or weeks. There is no rhyme nor reason to when it happens.
I have replaced thermostat & temp sensor. Radiator hoses all check out OK. It has both a direct drive fan and an electric fan, and both work fine. I've seen threads about water pump vanes corroding, but seems this would show up consistently as an overheating issue.
So, I suspected a head gasket leak, slowly pressuring the cooling system until it blows out. Nope. Just had the head removed by local mechanic, and no leaks were apparent. So, now I'm into a new valve job while the head is off being machined, and still no closer to solving this mystery.
If anyone out there has had similar issues, or knows what may be causing these random explosions of coolant, I would REALLY like to hear about it.

Thanks!!

cruiser54

Have you replaced the radiator cap?

Carlo Pelandini

So, my mechanic replaced the reworked head, installed a new water pump and new radiator cap. Tested mechanical fan: OK. I test drove it about 8 miles over some pretty rough back roads, all OK. It's been hot here (in the high 90's) so we took it to the river, (around 25 miles away), up, down and over a canyon, then down some gnarly rocky roads into another canyon, drove around in the sand and 4-wheeled a bit, back up the canyon, back over the same canyon to home. All OK. Then went to the store (about 4 easy miles away), and it puked coolant all over the parking lot!!!. Temp guage never went over normal. Drove it home and radiator was still full.. (What!!!.???)
I'm really at my wits end.. Wondering if MAYBE the transmission cooler in front of the radiator may be contributing to this??

I'm open to any suggestions or random ideas that may explain this..

Thanks!!

Carlo