[FarleyBob]

My 97 TJ with 4.0 manual has run great until today! On the way to work I suddenly had my temp guage head for the redline! I'm parked at work and the TJ is sitting out in the rain cooling off. What should I look for first? I'll check coolant level as soon as she cools ..........Water pump? Fan Clutch? Radiator?

Thanks,
Bob

[rljsrubicon]

If it started as you were tooling down the road at speed, it's probably not the fan. It could be, but a fan will normally cause problems sitting in traffic or going slow. Did you see any steam or anything? How fast did it hear up? Ron

Originally Posted by FarleyBob

My 97 TJ with 4.0 manual has run great until today! On the way to work I suddenly had my temp guage head for the redline! I'm parked at work and the TJ is sitting out in the rain cooling off. What should I look for first? I'll check coolant level as soon as she cools ..........Water pump? Fan Clutch? Radiator?

Thanks,
Bob

[doc_floyd]

Since the elements of the cooling system are:
a) The plumbing - channels, holes
b) The coolant
c) The water pump
d) The thermostat
e) The radiator, and
f) The fan;

Then either coolant is flowing and the fan is not working, which doesn't seem to fit the scenario, or
Coolant is not flowing - which could be due to clogging in the plumbing, or more than likely a thermostat stuck in a closed position. Not all thermostats are fail-safe in nature, i.e. if they stick, they stick in an open position. Water pumps don't usually fail catastrophically without a lot of noise.

[thesherm]

... or the heater core

[Combatsylvania]

X2 on checking the t-stat / replacing it

[cookeab]

It can be something as simple as a bad cap.

[bruker]

This doesn't help your problem but if it happens to you again turn the heater and the fan on full blast. That will help to get the temperature down.

[FarleyBob]

Thanks for the tips guys, I did a quick flush and fill of the radiator at lunch because the antifreeze looked pretty old. I've got it running now waiting to get up to temp and see what happens.

[jeeptillidie]

Im voting for stuck thermostat. If that is it you can take it out while you drive to go get another one and you wont overheat.

[FarleyBob]

It's running fine at normal temp right now. I think I'll make a run to the parts store for a thermostat and see what happens when I get the rpm's up a bit.

[ChuckDee]

I just had the same thing happen Thursday. Jeep has been dead on at 210F for the last two years, suddenly the check guages light comes on and the temp is in the red.

Today I replaced thermostat, then water pump, upper & lower radiator hoses, cap, belt, and finally radiator. Turned out to be the radiator.

Here's a tip to diagnose the radiator ... when the temp gets past 210, feel the upper and lower radiator hoses .. if there's much of a difference you have restriction in the radiator. Thats exactly what I experienced, top was red hot, bottom was ice cold.

Anyway, got an all new cooling system now .. about $400 later.