My 1994 Explorer is running hot. Can anyone out there help me to decide the next step in the diagnosis and cure of this problem?

Yesterday while in stop-and-go traffic with the A/C on I saw that the temperature gauge was pinned all the way to the right on the red line. Other than this, there were no symptoms of overheating (no steam, no smoke, no pinging noises). However, the A/C stopped working. I do not know how long the gauge was like that before I noticed it.

The A/C worked again when the car cooled down.

Recent engine work includes a new catalytic converter, oxygen sensor, fuel pump, fuel filter.

The vehicle has 138,000 miles.

Yesterday I searched this forum for advice and learned that one common cause of overheating in Explorers is the fan clutch wearing out.

I drove home from work today with the A/C off, the windows open, and the heat on full blast in 85 degree weather (on a hot day in Pittsburgh). This did bring the temp gauge down--to a level which was still to the right of the "L" in NORMAL--but, at least not in the red zone.

I went to see a mechanic today. He is almost retired, so he doesn't work many hours anymore, but he gives advice.

He looked at it and saw that the fan was cracked in several places. He said that wouldn't cause the problem, but that it would still need to be replaced before it shatters and does more damage. He thought that the truck was not actually overheating, since there were no symptoms of such. He said that perhaps I had a bad temperature sender or a bad temp gauge in the dash.

The top hose of the radiator was quite hot to the touch. There was no fluid leaking onto the ground. I figure that since running the passenger compartment heat brought down the engine temp, this proves that the water pump is working, since it is cycling water through the heat exchanger. Furthermore, since the top hose got hot, this proves that the thermostat is opening, and that water is flowing. So this lead me to two likely culprits: either the fan clutch was not providing enough cooling airflow, or, the radiator is clogged up and not allowing adequate heat exchange.

I went to the FORD dealer. They were surprised to hear that I did not want them to diagnose the problem (for $63), and that I simply wanted them to replace the fan, fan clutch, and temp sender.

I figured this was a safe gamble, since the fan definitely needed replacement anyway, the clutch might as well be replaced while they were in there (on a clutch with 138,000 miles), and, replacing the sender would be cheap. So I was proud that I had saved the $63.

Well--I lost my gamble! They did the above work for $240, and the truck still runs hot, just as before.

The new fan does make more noise, and it does offer more resistance to turning by hand (with the engine off) than the old one did.

So what do I do now?

If I could somehow connect a thermometer to the coolant, I would know once and for all if the car really is running hot, or if it is just that the gauge in the dash is wrong. (Should I rig up a meat thermometer in the circuit, or can a repair shop measure the running temp?)

If I find that it really is running hot, would I then check the radiator to see if it needs to be flushed out or rodded?

Could this still be a thermostat problem even though there is evidence that the water is circulating?

What about the water pump? Could it be the problem even though it is not leaking, and even though water is flowing?

I would appreciate any advice on these matters. Thanks in advance.

-Jon.

 

Excess heat is definitely not your friend! My thinking is that you're having a problem with coolant flow. Could be a sticking thermostat which is easy enough to change. Could be some radiator clogging. I think I'd stop at a radiator repair shop and let them do a "flow test". It's relatively inexpensive and gives a really good indication as to whether or not your engine is circulating enough water to provide adequate cooling. A corroded water pump can also slow ciculation even though it's not showing a tell-tale leak at the weep hole. Keep an eye on coolant levels. there's always the possibility of a leaking head gasket. Exhaust gases blowing back through the radiator may not immediately show a loss of coolant but will definitely make your engine run hot. Bubbles in the radiator and discolored coolant can be a clue for this problem. Best of luck....mike

 

Hi.

I just thought that I would post the solution to the problem here, just in case someone with a similar problem searches the site for answers in the future:

I had a thermostat put in and that solved it. The truck now runs with the temperature gauge right between the "O" and "R" on "NORMAL."

The mechanic said that the old thermostat was stuck at about 3/4 open. This explains why the top hose did get hot, and why turning on the heat did cool the engine somewhat. Specifically, there was coolant circulating through the system, but just not enough to cool the engine sufficiently.

The air conditioning works fine now, so I guess that the reason it had trouble before was the hot-running engine.

Thanks for your wonderful web site.

Jon.