bayhunter

My 99XJ overheated on a 3 hour road trip bout 2 hrs in . Pulled over and had shop replace t stat. IT WAS FINE REST OF TRIP . On way home back to 260 degress . IT seems like when runnin at 75 plus mph it heats up a nd when i drop down to sixty it runs normal. ANY SOLUTIONS?

djb383

Try replacing the radiator and water pump. To be on the safe side, new fan clutch, hoses and rad cap as well. A good flushing and fresh coolant never hurts.

bayhunter

I was thinking it may be water pump,but it dosent have any play in it.

djb383

To inspect the water pump, it must be removed.....impeller blades must be intact and impeller itself tight on the shaft. The shaft can be tight but the impeller can be loose but u won't know 'till u remove the pump. Kinda the same way with the radiator.....it needs to be removed from the vehicle and the tanks separated from the core (by a rad shop), in order to internally inspect.

After the old water pump and radiator have been removed, carefully place them in the boxes that the new pump and rad came in and install the new pump and rad and get a good nights sleep.

letsgomuddin

one way to check a radiator in the vehicle, is by being up to normal operating temp and using an infrared thermometer, check for cold spots in the core. note that the lower portion of the radiator will be cooler than the top by nature. Other possibilities for your overheating would be the afore mentioned water pump but not the fans, at expressway speeds they don't do anything anyway, you get enough airflow through the front. Also, a bad head gasket will cause overheating at higher speeds.

bayhunter

changed radiator,water pump and factory t- stat w / vent hole on it. all is well even w/ a/c on in traffic.

djb383

Tubes in the rad core can be partially plugged internally, say half open for example......the restricted amount of coolant still flowing thru the tube will be hot, as indicated by the temp gun BUT, heat transfer from the tube to the fins and air will be greatly reduced......thus the possibility of overheating. Just because a temp gun says the area it's pointed at is hot doesn't mean coolant flow thru that area is 100% and heat transfer is at max efficiency.