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Weird cooling issue

B

Brad Klammer

NAXJA Forum User
Location
Surrey, BC
1999 XJ, 4.0.

Normally the truck temperature runs exactly in the middle at 100 but will sometimes spike up to 120 but will not go all the way to 125?

This ONLY happens when I'm in the city in stop and go traffic. It will NEVER occur when I'm on the highway.

When it gets hot like that I crank the heat on the inside and and at first it wont blow out hot air, but then it 'clicks' and all the sudden the air coming out of the vents is hot?

Has anyone had a simiar issue or know of a fix?
 
Your xj is supposed to run about 200-210 degrees...sounds like you have the wrong t stat and or your system needs to be flushed and coolant replaced..
 
I think the OP lives in Canada and his numbers are Celsius.

If you're not getting hot air out of the vents right away, then I'm lead to a couple of issues...

1) Air in your cooling system. Have you had any work done on the system lately? How are your coolant levels?

2) The Heater Core Bypass Valve is either not working correctly, or there's a vacuum leak to it. (I'm not sure if the later XJ's had them, it's a four-way valve thingie with a vacuum fitting on it that sits just before your heater core inlet & outlet.)

:)
 
Sorry, Canadian temps... 210 for you guys equals 100 celsius for me.

So, it runs just slightly higher than 210 on the hwy at all times. In stop and go traffic it will jump up to 250 (the first orange line) but will never get to the second orange line which would be 260. It will sit at 250 for a bit and then I crank the heat and it drops back to 210 like nothing ever happened???

I'm hoping its just my thermostat that's pooched...
 
XJPhoenix said:
I think the OP lives in Canada and his numbers are Celsius.

If you're not getting hot air out of the vents right away, then I'm lead to a couple of issues...

1) Air in your cooling system. Have you had any work done on the system lately? How are your coolant levels?

2) The Heater Core Bypass Valve is either not working correctly, or there's a vacuum leak to it. (I'm not sure if the later XJ's had them, it's a four-way valve thingie with a vacuum fitting on it that sits just before your heater core inlet & outlet.)

:)
Click to expand...

The jeep is new to me and the PO said something about having the cooling system flushed. The fluid levels are fine.

Good info on the heater core bypass I will def look into that. How would I check for a vaccum leak?
 
One way to check is just to look at the valve actuator - it's a vacuum motor with a little plunger on it that turns a lever. With the Jeep running, and someone in it, watch the lever as they cycle the HVAC controls from cold to hot. (Select 'Vent' function, and if that doesn't work, switch it to 'heater'.)

There's probably a better way to do it, but I'm not a mechanic. If the arm moves, then you've got vacuum. If it doesn't move, move it by hand, and if it moves then, well, you have a leak somewhere.

:)
 
Replace your mechanical fan's clutch--classic symptom, overheating in city, stop and go, the drive through line.
 
**** UPDATE ****

I replaced the mechanical fan clutch, and my problem still persist. The thing that confuses me is that it's not a gradual heat increase, it will be sitting at the correct temp and then just spike suddenly? It usually sits at the first red warning line and then just drops off?
 
Sounds like it could be the thermostat. Its cheap and easy to replace one. It should cost you about $5 U.S. and take about an hour for someone who isn't experienced with the procedure. I would flush the system at the same time which would add some cost and time to those guesses.
 
Brad Klammer said:
Yes, electric fan is working and I will replace thermostat tonight. Does it sounds at all like a water pump issue?
Click to expand...

Suggest you use a Stant Premium thermostat or one from the dealer. Nothing else. You might also use the opportunity to replace the cap just to rule that out as well.

Check the fins on the radiator and A/C condenser. Make sure they are clean.

Are you losing any coolant? Any leaks?


Report back.
 
A faulty, sticking, thermostat not opening properly will cause temp rises at any time ... not just at a particular vehicle speed.

For the cost of a thermostat tho ... replace it anyway.

Waterpump is a possibility ..... but since you have replaced the common fault item ... the fan clutch .... I would look at the radiator cap.

Its meant to maintain about 15psi ....
If it cant do that ... Then your coolant temps will increase - to what the real coolant temp is at whatever the psi is ... when the radiator cap function is failing.

e.g.

Water boils at 0psi ...... 210*
Water boils at 10psi .... 240*

If you gauge normally shows 210* ... a pressure loss in the system means your gauge will jump to what ever the real temp is ... rather than displaying the "pretend" pressurised temp.
 
good info from carves, a faulty cap will make the temp spike when it releases pressure.

I'd also try and verify that the guage is not playing tricks. It runs on some very small ohm ranges, possible that in your stop and go traffic you may have a wiring harness issue that causes the guage to go funky. Just another possibility.
 
It is most likely the mechanical fan... had a similar issue here in Kodiak. I was fine in the winter till I pulled into the drive thru at the McDonalds. temp went up till I got moving again. fixed it the next chance I had and never had a problem again.
 
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