Bleeding coolant after fillip

Hi all. Is the process of burping/bleeding air out of the closed system the same after you made your repair and topped off coolant vs. burping/bleeding coolant as you fill up?

My 1988 xj had a tstat gasket replacement finally. I was driving it with that leak and had no heat during that time. I replaced the gasket & tstat yesterday, and topped off a couple times. I have no heat and the temp stays under 210. Thoughts? Would the typical park downhill, crack open sender unit and bleed process work? I'm hoping to sort this out before my Tahoe trip this Sunday . Thank you, I hope this makes sense.

Happy trails,
-sheepinajeep


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Yes, the process will be the same. You better make sure it's not your heater core, though. It could just be air in the system not allowing the heat transfer but if you're temps are pretty stable, the core may be clogged. I'd seriously consider flushing the core backwards and forward to break anything loose in there and hopefully get you heat again.

dan1977p said:

Yes, the process will be the same. You better make sure it's not your heater core, though. It could just be air in the system not allowing the heat transfer but if you're temps are pretty stable, the core may be clogged. I'd seriously consider flushing the core backwards and forward to break anything loose in there and hopefully get you heat again.

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Ok thank you. I have gotten warm air a few times, but usually it's just slightly less cold air to just cold air.


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Do you have a heater control valve on that year? If so, check that it's working.

Slide the heater temp control knob all the way left, then go to the engine and note the position of the little steel rod going into the control valve.

Then slide the temp control to the right and see if the steel rod has moved. If not, your valve is bad or you have a vacuum disconnect from the actuator.

montanaman said:

Do you have a heater control valve on that year?

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Yes. As a bonus they are far less expensive than the HO years.

I've got heat! I bled the system with the loosen the sender method. Thank you for the help!


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Bent said:

Yes. As a bonus they are far less expensive than the HO years.

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Yup I have the same thing: rod connected to temp control that leads to a heater valve.


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Sheepinajeep said:

Yup I have the same thing: rod connected to temp control that leads to a heater valve.


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Just a side note. That pesky valve can be removed completely with no consequences. The cabin heat is controlled by a flap under the dash, not the valve.
I've done lots of them here in Arizona with excellent results.

Wait for the day when that POS valve decides to burst and empties all your coolant in a short time.

cruiser54 said:

Just a side note. That pesky valve can be removed completely with no consequences. The cabin heat is controlled by a flap under the dash, not the valve.
I've done lots of them here in Arizona with excellent results.

Wait for the day when that POS valve decides to burst and empties all your coolant in a short time.

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Um, yes and no. The heater control valve in the engine bay allows hot coolant into the heater core. By removing it, you're just allowing hot coolant into the heater core 100% of the time. The temperature of the air in the cabin is controlled by the blend air door in the HVAC box that you mentioned.

JeepNoob said:

Um, yes and no. The heater control valve in the engine bay allows hot coolant into the heater core. By removing it, you're just allowing hot coolant into the heater core 100% of the time. The temperature of the air in the cabin is controlled by the blend air door in the HVAC box that you mentioned.

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Whaddya mean, yes and no?

The factory eliminated the heater control valve in 1997. It's unnecesary.
All it can do is cause issues with no heat and exploding at the worst possible time.

This picture gives you a pretty good idea of how the HVAC system and the mode door works. It's possible that the mode door actuator can fail which can cause the door to be stuck in the full cold or full hot position. If it fails in the full hot position and there's no heater valve to block off coolant flow to the heater core, you're gonna have heat in the cabin all the time. Granted, you might not be circulating that hot air, but my heater core can still keep my cabin pretty toasty even with my blower on the low setting.

JeepNoob said:

This picture gives you a pretty good idea of how the HVAC system and the mode door works. It's possible that the mode door actuator can fail which can cause the door to be stuck in the full cold or full hot position. If it fails in the full hot position and there's no heater valve to block off coolant flow to the heater core, you're gonna have heat in the cabin all the time. Granted, you might not be circulating that hot air, but my heater core can still keep my cabin pretty toasty even with my blower on the low setting.

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That's a stretch. It's cable operated.
Never seen it happen.
I've been around the XJs since 1984.
What is your resistance to removing the HCV when it's proven to be an effective mod?

For one, I figure if it's not broke, don't fix it. Second. my A/C probably isn't the best to begin with and I'd just rather not have a hot heater core in my rig 100% of the time. I've had my XJ for something like 2 1/2 years now and I haven't noticed one bit of trouble from my heater valve. Have I seen some stupid things on cooling and heating systems before? Sure. I think the inability to reach the radiator drain on an XJ is a big one. To me, the heater valve isn't one of them. Besides, I have screw-type hose clamps on every hose in my cooling system and I generally roll around with a little box of bolts in the back. If the heater valve cracks and is losing coolant, remove hoses with Leatherman, shove a bolt in them, crank down on clamp screws with Leatherman, drive to nearest gas station for coolant. Hell, if you were really desperate, you could probably top it off with straight water and be fine. Doesn't really sound like the life-and-death, leave you on the side of the road to be murdered by highway bandits problem you're making it out to be. FWIW, I think mine is still the original, quality OEM one...

Unfortunately, that is not the way the plastic valves fail. They split apart puking 2/3 of your coolant in an instant. Add a gallon of coolant to your toolbox. Yes, it will leave you stranded. It's a catastrophic failure of a cheap plastic part that's old. It's not just a little pissy leak.

I'm no rookie to these Jeeps.

I reached under the hood of my wife's 88 to remove the oil filter on a hot engine and had one explode and cover my face with 200* coolant. No warning. No previous leaks. I think I bumped it with my elbow.

To me, as I have proven numerous times with actual experience in the state of Arizona, This is a preventative maintenance procedure with no ill effects.

An upside to this is that coolant is always moving through the heater core and not stagnating in it for many months of the year.

Do as you like, but I want others to be well informed.