Another overheat thread...

I've searched several and haven't found one similar to this yet:

Conditions:
Outside air temp: 100ish
Wheeling slow in 1st gear
AC- On
2000 XJ A/T

My jeep usually runs a "little" hot, around 215-220. I normally attributed this to being in the high desert and the outside air always being hot.

Yesterday I was going down a rocky road at 3-5 MPH with the AC on and the temp jumped from its 220 to 250 INSTANTANEOUSLY. The check gauges light accompanied the jump. I turned off the car for about 15 minutes and then checked again. The temp needle went up to 250 and then climbed to 260 so I shut off the ignition and waited another 15 minutes. At that point I checked the engine and the temp was 220ish again so I restarted the engine. At steady idle with the AC off, the engine cooled itself back down to 215ish. The fan sounded like normal operations with it clicking on when the engine was a little hotter and turning off as the needle approached 210.

Any thoughts on where I should start troubleshooting? Wife says I can't take her wheeling again until this "problem" is sorted out.

Sounds like a stuck thermostat.

bics90xj said:

Sounds like a stuck thermostat.

Click to expand...

I'll put that on the list of things to replace.

I've also heard that this may be a symptom of a blown head gasket. What else can I do to rule this problem out?

Age of rad? Last flush? when was t-stat replaced?

scottmcneal said:

Age of rad? Last flush? when was t-stat replaced?

Click to expand...

Original radiator circa year 2000
Last Flush - Unknown
Last Tstat - Unknown

I've owned it since April when I bought it with 113K miles.

Sir, we can start here, flush, t-stat,... can you see if the water is moving with cap off? When you take off your cap, replace with new one...Find a rad shop if you can't flush it yourself. 8 yrs is a long time

scottmcneal said:

Sir, we can start here, flush, t-stat,... can you see if the water is moving with cap off? When you take off your cap, replace with new one...Find a rad shop if you can't flush it yourself. 8 yrs is a long time

Click to expand...

Thanks for figuring out that I'm new to this without asking.

Will the coolant flowing with the cap off be obvious?

Do you always have to replace the cap if you take it off?

Are there write ups for flushing your radiator?

Thanks for figuring out that I'm new to this without asking. We all start some where.. Do you have a manual for your jeep?

Will the coolant flowing with the cap off be obvious? Yes, when t-stats open

Do you always have to replace the cap if you take it off? No sir, just thinking it is old too

Are there write ups for flushing your radiator? Yes sir i think i have seen some

For future reference, if your temps start to jump up like that, instead of just turning the motor off, try turning off the AC, getting the electric fan going (may have to wire up a switch cause they like to turn off when the AC goes off), open all windows and crank the heat. If you're in an area that will allow you to drive faster, do so. Just shutting it down won't help the cooling. At the very least, shut it down and wire the electric fan to keep going. Oh yeah, and pop the hood too, that helps get a little heat out of the engine compartment.

Simply turning off a hot engine and waiting is the slowest way for the engine to cool down. If you're moving so slow that no air is circulating, while this is probably debatably a good thing, I would throw it in neutral and rev the engine to get more flow outa the fan clutch. Oh, fan clutch, another item to check!! Back when I had an MJ with no electric fan, when I was crawling in the heat for long periods of time, I'd have to throw it in neutral and keep the motor above 2k for a while to get the temps to go down. Take the load off the motor and increase the airflow through the radiator is the idea. I know, revving a hot motor up doesn't sound like the best of ideas, but it does get the job done most of the time. Lastly, if you need to rev the motor to get the engine to cool down, obviously, your cooling system is lacking!!