1996XJSport

This problem is usually native to diesels; but I'm pretty sure my Jeep is underheating. It's been really cold here in michigan for the past few days (I'm talking 2-5 degrees and about 10-20 degrees below zero with the wind chill taken into consideration). My XJ struggles to have any heat blowing inside even after driving for 10-15 minutes. I put my heater on full blast and in vent mode (which is usually the hottest) and I'll get mildly warm air, not enough to warm the interior at all.

Is there a fix for this? I might even have bubbles in my cooling system and if it's the case, how am I going to burp it?

Thanks in advance.

djb383

T-stat possibly/probably stuck open. Can u borrow a infrared point-n-shoot thermometer to verify engine coolant temp? Point it at the t-stat housing.

1996XJSport

I don't think it's the thermostat. The problem might have been caused by an incident a couple weeks ago where this kid in my shop class touched my radiator cap and didn't tighten it up and I drove home, ending up with almost no coolant. I had to add coolant the old fashioned way (without a coolant exchange machine) and I bet there's bubbles in there but I did hear that it will fix itself just by running the engine. I doubt that's true lol. Any way I can get rid of the bubbles without the help of a machine?

Update: you already know about the issue I'm talking about lmao

djb383

Surely your shop class has a point-n-shoot infrared thermometer.....no? I forgot, no temp sending unit, right? Usually, air in the system causes overheating.

Teflonchef

Back flush the heater core.

tjwalker

Do you have a coolant temp gauge in the dash? If so, what does it read?

Cab heat is simply a byproduct of engine heat, so verifying coolant temp. is job #1.

If no gauge, then verify with an infrared as djb383 mentioned......

The target for the 4.0 is around the 200-210 farenheit range.

Gotta start there.

1996XJSport

They have an infared thermometer, but I don't have class at all this week so I'll probably just stop by a friend's house because he has a heated garage and one of those point and shoot thermometers lol.

Yeah, no temp sending unit, I can tell either if it's running at an "alright" temp or if it's about to have a meltdown haha.

jeans

If its reaching operating temp and you have back flushed the heater core, id check the blend door on the heater hose going into the core. It may be stuck.

1996XJSport

Yeah my other XJ runs normally at around 210 at full engine temp. It doesn't look or feel like my Jeep is overheating whenever I drive it. The hood feels about normal temp or even colder if I put my hands on it after driving around and there's never steam billowing out of the grille when I stop so I have no clue. I guess I'll find out when I get to use a thermometer lol

djb383

Point the infrared at the heater hoses also. How can u determine all-right vs meltdown?

1996XJSport

I flushed out my entire cooling system back in November. I used a coolant exchanger at my school's shop to get the job done. It pumped out all of the dirty existing coolant and then I flushed the system one more time with a garden hose and repeated the process before filling it with new coolant. I'm going to see how hot my heater hose is after taking it out for a spin. If it's hot, im betting that blend door is stuck.

1996XJSport

Will do. The reason I can tell the difference between meltdown and safe is because the stock Cherokee SE's had an idiot light that would come on if you were overheating. Since the temp sending unit hasn't been changed from the "on/off" type to the actual reading type, The needle on the new gauge cluster will just go from all the way to the left to all the way on the right in the event of an overheat.

jeans

Even a coolant evac machine my not get all the guck out of the heater core. (There a decent machine, but you can do just as good a job without one). Look up heater core backflushing in the search. Ill bet you find a good write up. Most of the ineffective heat complaints for XJ`s are clogged heater cores.

sv41878

It's the cold and the excellent XJ cooling systems. I drove from Central NY to Southern PA today and it didn't reach operating temp til I got where it's 30 degrees. Also, check the vacuum line on the mixer (by the dip stick). If that isn't on, or leaks, the doors in the heater won't open right and it won't blow hot air.

To get the air bubbles out, start it cold without the radiator cap on and with the heat on high, wait til it opens the thermostat and fill. Do this once a day for 2 or 3 days and there will be no more air bubbles

djb383

That's a good one.