'97 Explorer Engine Temp issues

[Andy Corwin]

97 Exp 4wd 4.0L V6 SOHC I start the engine, temp gauge reads cold. I let it warm up just enough to where the temp gauge starts to move, then drive it just a few miles. Needle jumps to HOT fairly quick and the check engine light comes on. I turn on the heater to HOT, an the needle drops like a rock back to what I would consider normal and the check engine light shuts off. I can sit and idle and the gauge stays pretty much where it is. The coolant resivior was a little low so I filled it to the "cold" line after the engine completely cooled, but it happened again. Any ideas? I'm not a do-it-yourselfer, but before I take it somewhere I'd like a hint as to what it might be.

Thanks.

 

[RickOTR]

I would first check to see if you have air in the system. How many miles on your X? has the radiator ever been replaced, what about thermostat, the heater core back flushed, hose's ever been replaced. Maybe a failing water pump. Has the system ever been flushed and filled? These are just a few things to check.

 

[8TZX]

You may want to check your radiator cap, I had an incident where my temperature gauge pegged high, I immediately pulled over and had coolant escaping thru my coolant recovery tank, The upper radiator hose was sucked in. I removed the radiator cap which equalized system pressure. I replaced the radiator cap, added coolant and engine temperature returned to normal.

 

[donalds]

Sounds like a bad thermostat. Just saying

 

[German Engineer]

If I remember right, then the temperature gauge has a sensor that is all separate from the coolant temperature sensor.

If you have an OBD2 scanner look at the temperature in the live data and see what that says, and then compare to what the gauge in the dash tells you.
The ECM (the on-board computer for the engine management) uses the data from the coolant temperature sensor. If that sensor is bad it should likely throw an error code and a check engine light.

It's very possible that you may just have a faulty gauge in the dash or a faulty sensor on that, or an electrical issue with it.

 

[Andy Corwin]

If I remember right, then the temperature gauge has a sensor that is all separate from the coolant temperature sensor.

If you have an OBD2 scanner look at the temperature in the live data and see what that says, and then compare to what the gauge in the dash tells you.
The ECM (the on-board computer for the engine management) uses the data from the coolant temperature sensor. If that sensor is bad it should likely throw an error code and a check engine light.

It's very possible that you may just have a faulty gauge in the dash or a faulty sensor on that, or an electrical issue with it.

You are talking WAY over my head. AllI know is the temp gauge goes from C to H, the check engine light comes on. I turn the heater on high, it goes back down pretty quickly.

 

[donalds]

Again thermostat
I would also replace the thermostat housing with a metal one
Do a flush replace coolant

 

[German Engineer]

The car has two separate temperature sensors, one for the gauge in the dash, and a second (more important) one for the computer in the car.
So comparing those two temperatures can tell you whether it's more likely to be a temperature problem or just something electric instead.

But when the check engine light comes on and turning the heater on 'resolves' it temporarily, then this will likely indeed be a problem with the engine really starting to overheat.
But nontheless it's still worth comparing the two temperatures from both sensors in the dash and in the live data from the on-board computer.

If you know your way with computers well enough, then it could be worth buying an OBD2 scanner that can read out the live data.
These days OBD2 code readers are cheaper than what you pay a mechanic to roll up his sleeves before they even touch your car.

 

[Mbrooks420]

One time turning the heater on won’t work, then you run a real risk of ruining your motor.

Did the radiator suck up the coolant in the reservoir? I’d pull the radiator cap and start it cold. Let it warm up and add mixed coolant as needed. Putting it on ramps can help remove trapped air. (Usually trapped air ends up in the heater core, which apparently you don’t have an issue with)

 

[German Engineer]

Oh, and check if the big fan at radiator comes on or not when the engine is warm.
A broken fan can also cause some of the symptoms you mentioned.
(But if the fan doesn't come on, then don't just go ahead and replace it before checking other things as well first like wiring, or - as already discussed - checking for bad temperature sensors.)

 

[Mbrooks420]

Oh, and check if the big fan at radiator comes on or not when the engine is warm.
A broken fan can also cause some of the symptoms you mentioned.
(But if the fan doesn't come on, then don't just go ahead and replace it before checking other things as well first like wiring, or - as already discussed - checking for bad temperature sensors.)

Crank driven fan. Clutch could still be bad, but it wouldn’t overheat at speed for a fan clutch.

 

[German Engineer]

Crank driven fan. Clutch could still be bad, but it wouldn’t overheat at speed for a fan clutch.

Without the fan running it won't overheat when driving at speed, but when just driving around a few miles downtown with traffic lights and stop and go traffic it sure can.

 

[1998Exp]

I doubt that the CEL turns on and off, just like that. Could the O/P be calling the red "check gauge" light a "check engine light?" That one turns on when any gauge is out of normal range - including the temp gauge.

 

[Mbrooks420]

Without the fan running it won't overheat when driving at speed, but when just driving around a few miles downtown with traffic lights and stop and go traffic it sure can.

I mean, yeah....... that’s why I qualified it with “at speed”. It also wouldn’t do it in stop and go traffic, if it were blowing a gale, if you want to get entirely technical. Or, if it were -40.

I doubt it’s the mechanical fan, in any case.
Did the coolant you put in the reservoir disappear?