What would cause a Jeep Comanche to overheat?

Answer 1

There are a great number of reasons why it might overheat and it depends on the driving and weather conditions as well. The first thing to check is the oil level, coolant level and condition. Low oil/oil pressure will cause an overheat. For coolant...(When was the last time the system was drained and flushed?) If the coolant is cruddy, then the system is dirty and the radiator isn't going to be able to dissipate heat. The second thing I'd check is the thermostat. When it's working toward overheating, is the upper radiator hose hot? If it's not, and it's above operating temperature, chances are that you either have a sticking thermostat or one that is set to run hot. Thermostats are inexpensive, don't take very long to replace yourself / don't cost much if you have it done. The third thing that often contributes to overheating is the mechanical fan clutch. Are you overheating at speeds over 35 mph, or just slower? The fourth item is the electrical fan. Does it come on? You can test this by turning on the A/C and when the compressor kicks in, it should turn on the electric fan. If it does not, you can check the fan, the relay and the fan diode (which sits inline in the wiring right by the air filter box. I run a 4.0L engine and a new stock radiator. I chased an overheating problem for many years before I realized it was a corroded radiator. That said, now it's a different story. Even on 90 degree days, it rarely pushes over 212 in traffic using a 70% antifreeze severe winter rated blend. There have been periods where I've used 30% antifreeze during the hot season and have never had it rise above operating temperature even with the A/C on in stop and go traffic.