Overheating on Jeep Cherokee

1993 Jeep Cherokee, 4.0L I-6, 215K miles

This is my stepfather’s Jeep. It would read fully into the red when the A/C was engaged, and cool back down when A/C was turned off. He put a new temperature sensor and thermostat in, and noticed that the gauge now doesn’t read quite as high as it used to (looks like he replaced the sender and not the sensor, are they separate on this vehicle?).

However, it still reads very nearly into the red when the A/C is engaged. He tells me it loses some coolant, but there are no external leaks. The head gasket was changed sometime last year. My guess is that the radiator is plugged up and just can’t efficiently do the job anymore. What’s everyone else’s opinion?

Maybe cooling fan not up to par or poor head gasket job. I’ve seen the results of a head gasket replacement WITHOUT a torque wrench.

You might check the cap on the tank. I had one that went bad and could not see the problem. replaced the cap and no problem.


The cap on the reservoir tank?? Never heard of that being able to cause an overheat condition, but we’ll look at it.

Anyone have any other thoughts?

I think he meant the pressure cap on the radiator. Can you see if any tubes are cogged? Is it a plastic/aluminum radiator? If so, and it’s clogged, you’d need a new one (check the internet and parts store, not the dealer).

I’m leaning towards a partially restricted radiator. Afterall it is fifteen years old.

When the A/C isn’t on, the radiator has sufficient cooling capacity to prevent the engine from overheating. But when the A/C is used, the extra heat from the condensor passing through the radiator diminishes the radiator’s ability to remove the heat from the engine coolant. So the engine begins to overheat.

One way to check for this is to point a thermal laser gun at the radiator as the engine is running and hot. As the gun is moved across the radiator cores, the restricted cores will have much lower temperature readings than the cores that have hot coolant passing through them.