Sticking Thermostat?

[brad9798]

I'm no mechanic, but I can fix things mostly on cars. Don't like to, but will.

Anyway, Jeep Cherokee (4.0L inline six) is having (I think) thermostat issues ...

Sometimes it runs right above 200f, and sometimes it stays down at about 125-130f.

Thermostats are easy to fix ... I think all I might need to do is drain a bit of coolant, replace the 'stat and seal and be done with it!

Or could it be something else ... like the sending unit? :confused:

IIRC, the sending unit is on the back-end of this straight sixes ... I think ... who knows.

Anyone have any direction ... or thoughts?

Thanks,

Brad

[davidagage]

Brad, thermostat sounds like the right thing to do. does the temp go up when running hard, but during normal times stays low? That would be a sign of a stuck open thermostat. It is a cheap and easy repair so I would go ahead and do it first. If it doesn't cure it then look at the sending unit...

[Uncle Duke]

What year is the Cherokee?
Some had 2 temp sensors - one to the computer (for emissions mapping) and one to the electric fan. One of those also goes to the guage, but I don't remember which one.
Is the fan on (indicating that the value sent to the guage is incorrect) when it reads 125?

[brad9798]

It is a 2001 60th Anniversay Edition. 61,000 miles.

No, the fan is not coming on ... so I think the guage is okay.

Thanks guys!!!

[Ken Hutchins]

First check the coolant level in the radiator when it is cold, the cap might need replacing, not allowing coolant to return from the overflow bottle. Full bottle doesn't mean full radiator.
Also checks for leaks top tank, tighten the crimps around the edge if necessary for a quick leak fix.

[Stiletto]

If the fan isnt coming on, you can confirm if the sender is the problem on a two wire system by making a jumper to connect both wires. The fan should then run all the time the ignition is on. Observe what happens to the temperature.
Make sure the water pump belt is tight enough.

[brad9798]

It just now was running cold ... put it in neutral and revved it to 4000rpm ... must have been stuck, as it almost immediately jumped to 205 ... maybe it is the guage or sending unit ...

[Tylerdurden]

That model cherokee has a clutch fan and on the drivers side a secondary fan (electric ). Usually its the thermal switch for the secondary. Its cheap so swap it out. If that doesn't do it pull the t-stat and do the pan on the stove trick (or swap it out). If the t-stat is +or- 10 degrees its good (should open smoothly on rise) if not replace it. Next is the clutch fan, if the clutch is worn she will freewheel until the bearings heat up.
If she isn't overheating I would figure the water pump is good (check for weeping out the seal hole)
If you have gone through all that and the guage is still wacky you problly have a bad ground.