[dogbluedrummer]

This past weekend, I started overheating after running in 4Hi all day. I came home and replaced the thermostat and topped off the rad and puke tank....that was on Sunday. Today, I did some moderate wheeling in 4LO for about 2 hours. I overheated again on the trail.

New 195 deg thermostat
Overflow tank was full (to the mark) on Sunday, empty tonight.
No peanut butter under the oil cap.
No oil floating in the radiator.
No white smoke out of the exhaust, and no sweet smell indicating a blown head gasket.
No overheating while driving on the roads (35 mph plus....wind helps).
Normal operating tem used to be 210, now it runs around 225.
Visible coolant sprayed all over the underside of the hood.
Sometimes a little rough idle at startup, but smooths out quickly.

When I overheat, I can hear the coolant boiling. Saturday it pushed back into the overflow tank, but not today. The rad hose running to the thermostat gets very firm, indicating high pressure. I believe the thermostat is open, because it's new. What would cause the pressure to be so high? Is this just due to the overheating? I did not see any hose blockages when I replaced the thermostat.

So, I am narrowing it down to 3 potential causes:
1. Leaky radiator cap
2. Bad water pump
3. Leaky radiator

I am leaning towards a bad water pump as this is the only one that would be consistent with the high pressure. Perhaps NO coolant is flowing, and it's staying cool by the airflow.

Any thoughts?

[hunter44102]

I think its your water pump, if its not moving the fluid, it will overheat.

[4.7stroker]

I would look at your fan clutch, if the water pump was bad it would overheat on the highway also.
You seem to have problems at low speed indicating not enough air going through the rad at low speed.
As an emergency measure.
Try this when wheeling put your heater on high and full hot, this will help you dump heat out of the cooling system.
I have had to do this on a few trips here when it was over 100*f my heep got toasty warm, dumping the extra heat prevented the coolant from boiling, I was quite hot though so I took the doors off so I didn't boil my skin off.


Dwayne

[ErnieG]

Originally Posted by 4.7stroker

I would look at your fan clutch, if the water pump was bad it would overheat on the highway also.
You seem to have problems at low speed indicating not enough air going through the rad at low speed.
As an emergency measure.
Try this when wheeling put your heater on high and full hot, this will help you dump heat out of the cooling system.
I have had to do this on a few trips here when it was over 100*f my heep got toasty warm, dumping the extra heat prevented the coolant from boiling, I was quite hot though so I took the doors off so I didn't boil my skin off.


Dwayne

im gonna agree check fan clutch

[DOG2000TJ]

Originally Posted by 4.7stroker

I would look at your fan clutch, if the water pump was bad it would overheat on the highway also.
You seem to have problems at low speed indicating not enough air going through the rad at low speed.
As an emergency measure.
Try this when wheeling put your heater on high and full hot, this will help you dump heat out of the cooling system.
I have had to do this on a few trips here when it was over 100*f my heep got toasty warm, dumping the extra heat prevented the coolant from boiling, I was quite hot though so I took the doors off so I didn't boil my skin off.


Dwayne

Originally Posted by ErnieG

im gonna agree check fan clutch

Don't overlook the water pump too soon. I had the same problem as the OP stated last summer while on vacation. I was running around town and while moving the temp was normal. When I came to a stop the temp shot up to the red and antifreeze boiled over.
I brought it in for service immediately. The mechanic chaged the t-stat and replaced the antifreeze, let it sit at idle for 15 minutes and she was fine. 3 days later the same problem comes right back. Temp is fine while moving but shoots way up and boils over at a stop.
So I bring it back in again and insist on taking off the water pump. Sure enough, the water pump that was installed just 3 months earlier was broken. The pump wheel was plastic and broke off at the hub.
So a new water pump, all metal, was installed and no problems since.
God luck, take care of your ride.

[80 CHOPPER]

Spin the fan, if it free spins 5 or 6 revolutions, the fan clutch is bad.

[dogbluedrummer]

Originally Posted by 80 CHOPPER

Spin the fan, if it free spins 5 or 6 revolutions, the fan clutch is bad.

I did the spin test, and I get a little less than one full rotation. Clutch is good.

[mrfast]

sounds like a bad cap or you could have got a bad thermostat.

have your mechanic do a pressure test I bet either your water pump seal or radiator tank is leaking under high pressure.

[rmack]

check your radiator. look were the tank and core join together for signs of a leak. also remove the cap and look to see if the core plugged up.

[Skagdog]

I know this an old thread but I have some input. Start your jeep from a cold engine and wait til your t stat opens (upper radiator hose gets hot) If it doesn't, your tstat isn't opening. If it does open, let your jeep run a couple more minutes then turn it off. Carefully (and I mean carefully) feel the radiator for cold spots. If your radiator isn't uniformly warm, you've got some blockage that needs to be addressed. sNAPA sells some power crap you can put in there (not radiator stop leak) that will dissolve solids and clean the cores. Flush it a couple of times and repeat the test from cold again. If your radiator still has extreme variances in temperatures in different places you need to think about swappin' your radiator out for one without contaminants.