after much searching....temp issue ?

First off i am running a 97 xj with the 4.0 and ax15 manual transmission. 3 inch lift with 31x10.5's and about 215k miles on her.

About two months ago i started having overheating issues. I would be driving for about 15 to 20 minutes and out of no where the temp gauge would jump from around 210 all the way up to red lining. to fix the problem i turn the heat on and after about 5-10 seconds the temp gauge jumps back to normal. i turn the heat back off and am good for about 3-5 minutes until it jumps back up the pegging out the gauge. this continues with no end till i turn the jeep off. if i do it enough times(like the first time when i had to get home) the overflow tank will overflow fluid.

So far i have replaced the water pump, thermostat, temp sending unit, coolant flush. about a year ago i put in a new radiator, upper and lower hoses and a new fuel rail and injectors. i have run the jeep with the radiator cap off trying to flush any air that might be in the system.

Any help would be amazing.....my boss is not so cool with me borrowing my work truck anymore....

Thanks

Danny

Install a new radiator cap.

Overheating cooling system

Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a slipping fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller or even a defective radiator cap.

The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic points to a weak or failing mechanical fan clutch.
The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.


-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With a neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak. -Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –

www.offroaders.com/tech/engine-overheating.htm

www.familycar.com/classroom/coolingsystem.htm

Dunlapx said:

First off i am running a 97 xj with the 4.0 and ax15 manual transmission. 3 inch lift with 31x10.5's and about 215k miles on her.

About two months ago i started having overheating issues. I would be driving for about 15 to 20 minutes and out of no where the temp gauge would jump from around 210 all the way up to red lining. to fix the problem i turn the heat on and after about 5-10 seconds the temp gauge jumps back to normal. i turn the heat back off and am good for about 3-5 minutes until it jumps back up the pegging out the gauge. this continues with no end till i turn the jeep off. if i do it enough times(like the first time when i had to get home) the overflow tank will overflow fluid.

So far i have replaced the water pump, thermostat, temp sending unit, coolant flush. about a year ago i put in a new radiator, upper and lower hoses and a new fuel rail and injectors. i have run the jeep with the radiator cap off trying to flush any air that might be in the system.

Any help would be amazing.....my boss is not so cool with me borrowing my work truck anymore....

Thanks

Danny

Click to expand...

You dont mention at what speed this problem occurs and since you have addressed most of the system items; I did notice you have not replaced the thermal clutch assembly for the mechanical fan.
A malfunctioning clutch can cause overheating at slow and moderate speeds.

Thanks for all of that.

I did replace the radiator cap and no change.

the problem only seems to happen at 55 or above...both fans are working fine

if i had an exhaust leak into the head would the exhaust have any tell tail signs of that, or how would i track that down?

Just a note...I do not have an overheating problem (I did, but a wholesale change of the cooling system fixed that), but I have noticed that it has been running higher than I would like it to lately. Then I found out I had a failing cat and a bad downstream O2 sensor ('96 XJ, OBDII). I replaced the cat and O2 sensor, and after the computer re-mapped itself, my temps went right back to normal. I believe that the failed cat and sensor caused the computer to adjust the timing too much trying to lean the engine out, which is another cause over overheating.

Just something to add to the list of things that can cause an engine to overheat.

I would want to make sure it is really overheating. If the gauge or wiring is faulty, you can replace the whole cooling system and still peg the gauge. I use a non-contact infrared thermometer to check the gauge, focusing it on the temp sender. You haven't mentioned if you're getting coolant bypassing the pressure cap?