I have replaced radiator, thermostat, lower radiator hose with spring in it, temp sending unit, temp sensor, tested aux fan new water pump. Aux fan will not come on unless you unplug temp sensor, and i can not get the air bubbles to stop coming up through radiator. 95 cherokee sport 207,xxx miles. Is there anything i may be over looking?

 

Compression tests on all cylinders?

 

First fix the bad temp sensor. Boiling the coolant may be the source of you air bubbles. Do the compression test.

 

Temp sensor is brandnew. Just put it in last night if there is air bubbles in the system it wont work will it?

 

In the 91-01, the system usually does a good job of purging air within about 3 complete heat up and cool down cycles.

A compression test is never a bad idea. For the 4.0, you are looking for 120-150 psi, with no more than a 30 psi variation between cylinders.

 

pressure test the radiator/svstem

 

And then test the coolant for combustion gasses.

 

Check the oil, if you have a bad head or gasket it will probably show up in the oil. Any white smoke coming from exhaust, another sign of head problems. Do the compression to be sure. Is it overheating or just the bubbles?

 

Go borrow the tools from autozone to do a compression test AND cooling system pressure test. Test both the radiator and the cap when doing the cooling system pressure.

 

Testing it is the only way to know for sure, but oil in the coolant and coolant in the oil is also another way to check. And burning through oil is also a major sign. The last head gasket I know of that went, made the vehicle burn through oil like it was going out of style.