help

heres the prob i got. actually its my brother in laws. a friend of his replace the themostat and water pump. now it boils in the over flow after driving for about 3 min. the temp gauge dosnt read over 190 either .somone said something about vapor lock in the radiator. anyone have anything to say about this? TIA

i also forgot to add that his 88 xj is missing the aux fan. could this cause some problems?

If the temp gage says it’s good and it’s boiling over than the water is not circulating though the system. A number of things could cause this, the most likely would be inadequate purging of air from the system, but also could be a pump issue or a backwards thermostat or something along those lines.

can you refill the radiator by filling it up through the overflow or do you need to take the hose of the radiator a fill it that way

Who replaced the water pump and where did it come from?

The 4.0L block is the same as the older Jeep 258 (4.2L) block, and the water pumps will all bolt in. However, with a serpentine belt the 4.0L water pump rotates in the opposite direction of a water pump for an engine set up with vee belts. If the water pump is for/from a 4.2L application, the impeller blades are pitched "backwards" for the 4.0L and won't push any water.

That's my best guess.

Check the O-ring on the pressure bottle and back flush the coolant system. You can buy a kit at any auto parts store. This will help purge any air still in the system.