4.0l XJ overheating? Start here - the basics!

[werd]

Ok, what's the connection? How do those sensors make the car overheat, shutdown, without showing on the temperature guage or turning on the electric fan?

[anthonygubbin]

Originally Posted by junglejuice

Pretty common, it's one of the CPS's, either the cam or crank....

That was my thoughts.

Mine sits close to 95deg at normal running temp. I drive in minus 5deg temps and it sits near 95, where its suppose to. Well I thought that is about where it is suppose to sit.

Regards A

[anthonygubbin]

Originally Posted by werd

Ok, what's the connection? How do those sensors make the car overheat, shutdown, without showing on the temperature guage or turning on the electric fan?

As the crank sensor gets old it becomes more prone to failure when hot. When its on it way out it will be affected by heat. Its not to do with the fan or engine temp.

Regards A

[werd]

Originally Posted by anthonygubbin

As the crank sensor gets old it becomes more prone to failure when hot. When its on it way out it will be affected by heat. Its not to do with the fan or engine temp.

Regards A

Ok, I think I understand. This is why the car wouldn't start.

So then, why wouldn't the temperature guage show more than just under 100 when it was boiling? I was thinking maybe a faulty radiator cap as this would decrease the boiling point of the water.
I'm not sure about the temperature sensor as it does move up and down between 85 and 100. It would also explain why the electric fan didn't cut in

What do you think?

[Hamsteh]

Originally Posted by werd

Ok, I think I understand. This is why the car wouldn't start.

So then, why wouldn't the temperature guage show more than just under 100 when it was boiling? I was thinking maybe a faulty radiator cap as this would decrease the boiling point of the water.
I'm not sure about the temperature sensor as it does move up and down between 85 and 100. It would also explain why the electric fan didn't cut in

What do you think?

I think the other fellas, like myself, missed the first line in your post about the radiator boiling.

The only time mine has every boiled was when a plastic tee in the heater line collapsed, allowing pressure drop. My guess would certainly be a pressure leak of some description - radiator cap is a good starting point, along with all hoses and hose connections.

[junglejuice]

Originally Posted by werd

Ok, I think I understand. This is why the car wouldn't start.

So then, why wouldn't the temperature guage show more than just under 100 when it was boiling? I was thinking maybe a faulty radiator cap as this would decrease the boiling point of the water.
I'm not sure about the temperature sensor as it does move up and down between 85 and 100. It would also explain why the electric fan didn't cut in

What do you think?

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?

[Rodgebone]

Even with the internal heater turned on full the air was cold. And still the temperature guage hovered around just under the 100 mark until we got closer to home and it got a bit cooler, it stayed just above 85°c.

this statement stands out to me more than anything and no one has addressed this aspect of the problem. it sounds like a stuck open thermostat issue (85 is pretty cold for an xj on any day even in cold ambient temps). this begs the question: are there multiple faults here? possible heat soaking of the crank sensor for the no start issue plus a stuck t-stat or a collapse in the heater lines for the cold air issue from the heater vents inside the cab? what year is this car?

im also thinking if it has the temp gauge sender at the back of the head these are prone to failure and may have given false readings on the temp gauge (like when it boiled over but still displayed a relatively low temp gauge reading - it should have been in the red if it boiled over). i would be changing out the crank sensor and checking the temp sender for the gauge and the t-stat and heater lines to start. sounds like the car was actually overheating but did not display any red flags via the temp gauge. 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.