4.0l XJ overheating? Start here - the basics!

[bruggz351]

... one more thing to ponder...
... when I first got my XJ, the first sign of the blown head gasket showed when we shut-down after run. It was at running temp and as soon as it was shut-down it boiled it's nuts off.

cheers

[Billnick]

If the radiator cap is faulty and not holding pressure, as soon as the coolant temp hits 100* she'll boil. The coolant temp will never reach 105* for the electric fan to cut in.

[junglejuice]

Originally Posted by Rodgebone

none of this explains why the fan didnt kick in unless the pcm didnt see enough heat to turn it on which baffles me. it should have kicked in and stayed on in the ac/defrost mode or at least cycled in other modes (maybe not enough time for the temps to cycle the fan on and off after the no start?). just some more food for thought. very weird indeed.

This is why I asked if the fan works with the AC....

[94xjeep]

Well I found out that these adrad copper brass rads are not solid or stiff in the core like the original ones that are in the xj's plastic and copper core radiators. Due to the length of the core the rad gets a lot of expansion and the core starts to twist like a twisty and this shortens the core and make it pull on the tank header plates. The original jeep radiator core was ok the plastic tanks had let go and I had no over heating issues at all.

The adrad work well much better with the dimple tubes but you could see the difference in the core strength off the bat. My ZJ's genuine old jeep core was the same strength, fin count, tube size and the copper replacement I got was half the weight and you could bend the fins with the flats of your fingers easily. When I fitted my first new adrad radiator and pressure tested to 17psi(I go 1 psi over the rated cap) the noises coming from the rad made me worry straight away. IT sounded like rice bubbles but much louder. When I fitted the second one and pressure tested it to I thought great same noises again.

I have checked the gauge on the pressure tester with new radiator caps with the cap test fitting and they all blow off at the advertised cap rating so it's good. PS the e bay nang kang rad is still going and no leaks. that's 3 weeks on the road.

[werd]

Originally Posted by junglejuice

What year model do you have as if it's a pre-update the temp sensor for the guage has no influence on the fans.
The temp sender for the guage is at the rear of the head on the passenger side, the temp sender for the PCM which in turn is responsible for the fans is located in the thermostat housing.
Does your fan run with the AC?

Ok, this is what I know so far:

I couldn't see any sensor on the head rear passenger side. Not to say that there might be one as it was difficult to see/feel back there.
Date of car 10/97
AC - is not working, that's another problem.
Prior to this recent problem, I have heard the electric fan cut in.
Prior to this recent problem there was a DTC P0138 O2 Sensor circuit high voltage.
So today, I put a new radiator cap on and pulled the plug off the sensor on the thermostat housing and cleaned the plugs with contact cleaner.
Then I plugged in my laptop and started the car to check for DTC's.

Including P0138 the codes are:
P0138 Engine coolant temperature circuit high. This was because I forgot to plug the sensor back in. The fan was running and stopped when I plugged it in.
P0320 Ignition/distributor engine speed input circuit (I don't know what this one is)
And a pending code of P0265 Shift solenoid "B" performance or stuck off.
So I put a blanket in front of the grill and warmed the car up. I could hear the friction fan roaring into action and then getting quieter.
The electric fan cut in at 106°C and cut out at 102°C. I did this twice to confirm.
The outside temperature according to the overhead console was 17°C. Leaving the car to idle and cool down the temperature sat on 99°C before I turned it off 30 minutes later.
The temperature went as high as 107°C and never boiled once.
The above temperatures were taken from my laptop.
The temperature guage in the dash was reasonably accurate, plus or minus a few degrees.

[bruggz351]

Awesome, so it appears you found your problem... Glad it was a cap and not a head gasket..

cheers

[werd]

Originally Posted by bruggz351

Awesome, so it appears you found your problem... Glad it was a cap and not a head gasket..

cheers

Me to

I've got a new thermostat to put in as well. And then swap out the fan for an electric one.

Next I'll have to work out those other DTC's