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Discussion Starter #1
First off - I have replaced the follow parts in the cooling system within the past few months:

  • Heater core
  • Thermostat housing (which came with both thermostats)
  • Temp sensor
  • Performed a full coolant flush with Prestone flush cleaner, distilled water, etc. & bled the system of air
  • Filled it back up with the correct HOAT coolant
If I leave the Jeep to idle, randomly it will get up to operating temperature depicted by the gauge needle on the halfway mark. Usually, it will start heating up fine, but the needle will only reach halfway between the 1/4 mark and the 1/2 mark. It will even stay there as I am driving. I can get the needle to the 1/2 mark if I keep it at 2500 RPM for about 5-10 minutes. So I know my temp sensor is fine (I've also confirmed this with my OBD scanner).

Can bad thermostats cause this? The tstats that were shipped with this housing looked like cheap pieces of junk. And this is the second housing I've had to put in recently (broke the first one trying to get the tstat out) and both have been performing like this. I tested the main tstat in boiling water (~190-200 F) and it opened. But I think it's either opening too soon or not closing all the way. If I can rev the engine and get it up to operating temp. it seems like a tstat issue to me and not trapped air. I have two Stant tstats ready to install, but it's too cold to do anything right now.

What do you guys think?
 

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Discussion Starter #2
BUMP

So I used to think the lack of heat was related to the coolant temperature slowly getting hot... not so much any more. In the past two days, at idle and the coolant temp where it should be, my heat has gone from warm to cool now...

  • Heater core inlet and outlet pipes are hot
  • Coolant temp is fine
  • Engine is not overheating which makes me rule out bad water pump
  • Not leaking coolant - checked reservoir and it remains the same
  • Air gets warmer as engine revs
The only thing I can think of now is a blend door... does anyone have any experience with the blend doors on this vehicle? Or how to troubleshoot them?
 

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I don't have any experience with the blend doors on these cars but I think that is a good guess and the most likely culprit at this point.
 

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Discussion Starter #4
I don't have any experience with the blend doors on these cars but I think that is a good guess and the most likely culprit at this point.
But if the blend door was sticking or faulty, why am I getting hear when I accelerate? If the door was shut, acceleration shouldn't change that.
 

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That is true, forgot about that part. Is the blend door flopping and the mad G-forces of the Compass' furious acceleration causing the door to lean open? 😆

No actually, now that I think of it, are you sure your water pump is working 100%? You'd think if it wasn't that the car would overheat though...

Chrysler used to use these goofy valve things on some vehicles that allowed the coolant to mostly bypass the heater core in the summer (Ok, Chrysler wasn't the only ones to have those things probably). Have you followed all the lines and checked for any weird plastic things that might be for a heater core bypass such that that? If your car has such a thing it could be stuck mostly shut. Seems like their minivans used to have those... I'm not 100% sure I'm not making that part up though, never actually changed one just been told they were a thing.

I don't know why your car has two thermostats I've never heard of that. I have had a few times that thermostats were bad right out of the box, could try a couple new ones.

Something must be impeding the flow and the water pump only overcomes it when the engine revs up enough thereby spinning the water pump hard enough to overcome it. So like I said anything from a partially bad pump with some impeller fins missing or some bypass device for the heater core stuck shut or a new thermostat that is sticky or...

You should also check for any kinked heater hoses, happens easily if you 1) don't by the pre-bent hoses or 2) the pre-bent hoses are bent poorly. Just a small kink would slow down the flow a lot but maybe open up when the engine turns the pump faster and builds more pressure...
 

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Discussion Starter #6
That is true, forgot about that part. Is the blend door flopping and the mad G-forces of the Compass' furious acceleration causing the door to lean open? 😆

No actually, now that I think of it, are you sure your water pump is working 100%? You'd think if it wasn't that the car would overheat though...

Chrysler used to use these goofy valve things on some vehicles that allowed the coolant to mostly bypass the heater core in the summer (Ok, Chrysler wasn't the only ones to have those things probably). Have you followed all the lines and checked for any weird plastic things that might be for a heater core bypass such that that? If your car has such a thing it could be stuck mostly shut. Seems like their minivans used to have those... I'm not 100% sure I'm not making that part up though, never actually changed one just been told they were a thing.

I don't know why your car has two thermostats I've never heard of that. I have had a few times that thermostats were bad right out of the box, could try a couple new ones.

Something must be impeding the flow and the water pump only overcomes it when the engine revs up enough thereby spinning the water pump hard enough to overcome it. So like I said anything from a partially bad pump with some impeller fins missing or some bypass device for the heater core stuck shut or a new thermostat that is sticky or...

You should also check for any kinked heater hoses, happens easily if you 1) don't by the pre-bent hoses or 2) the pre-bent hoses are bent poorly. Just a small kink would slow down the flow a lot but maybe open up when the engine turns the pump faster and builds more pressure...
Thanks for taking the time to write a that.

  • I do not have any heater core bypass.
  • If my water pump had a bad impeller, I would think I'd NEVER get hot air at idle. But I do sometimes.
  • It is weird to have two thermostats, but that's how this car is set up. I have two inside the plastic thermostat housing. I've replaced the main one three times and the secondary one twice.
  • Definitely no kinks. I replaced those stupid bended hoses with normal heater hose so it's practically staright going into and out of the core.
I parked on my driveway today (sloped) and opened the radiator, installed my overflow funnel, poured some coolant in, and let it run for a good 1.5 hours. Every time the coolant fan would kick on, I noticed bubbles coming out into the funnel? Why does this only happen when the fans kick on? I'm thinking my issue is air, but I don't know how much is on the system. I hope it's not getting in somewhere because I can't stop thinking of a blown head gasket......., I pray that is not the issue.
 

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Like you, I have no experience with blend doors, but are they vacuum powered? At least they were on the older cars I owned. Now they're thermostatically controlled so a lot may have changed. Acceleration affects vacuum so maybe that's a cause.
 

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Well yes air would be a likely culprit. I'd ruled that out since you said you filled it. Maybe there is still air in there somewhere. I don't suppose you measured how much it took when you filled it. That could provide a clue.
 

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Discussion Starter #9
Well yes air would be a likely culprit. I'd ruled that out since you said you filled it. Maybe there is still air in there somewhere. I don't suppose you measured how much it took when you filled it. That could provide a clue.
The blend doors have an electronic motor. Not vacuum controlled.

And I didn't pay attention to how much I put back in. It seemed like less than the amount the Jeep takes. I figured that was from the residual left in there from the flush. If it is trapped air, holy crap it's hard to burp.
 

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Anybody here have a hayes or chilton manual covering that year and can check if there is anything special you need to do when bleeding the air out? You could also see if anyone on youtube has done a video for that car, maybe there is more than one place to bleed air out but you'd think it would work out over time either way, its been this way for you for a long time now.

Has the water pump been changed before?
 

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Discussion Starter #11
Anybody here have a hayes or chilton manual covering that year and can check if there is anything special you need to do when bleeding the air out? You could also see if anyone on youtube has done a video for that car, maybe there is more than one place to bleed air out but you'd think it would work out over time either way, its been this way for you for a long time now.

Has the water pump been changed before?
Yes water pump was changed a year ago. And if the pump was bad you'd think I would be seeing overheating issues, but I'm not.

What I do find strange is both MOPAR thermostats for this vehicle have been discontinued on MOPAR's website. So the ones I got from RockAuto - I'm not even sure they are correct. RockAuto doesn't even sell the secondary tstat. I'm wondering if the MOPAR ones had a higher temp. rating.

Also I do have the Haynes manual. The only thing I can see that I didn't do was unscrew the two block bleeder screws, but I've skipped that step before because they're stripped. Plus, like you said, the air should work itself out... One would think right?
 

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Discussion Starter #13
Yes, very much so because I'm wondering if I have a blown head gasket now and the cylinder compression is introducing exhaust gases into the cooling system thus creating the air pockets that I keep trying to bleed... I need to get a kit to test for exhaust gas in the cooling system...

Does anyone know of a method to manually pump coolant into the system to try and break up any clogs and force out air pockets? I thought about getting one of those pressure test kits for your coolant system... I know that introduces air into the system, but if I do have some weird trapped pocket, maybe that will clear it out.
 

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For older cars I used to have an adapter where I could hook up a garden hose to one of the heater core lines to flush it out, usually just put some scrap hose on the other end and ran it into a bucket. Not much pressure there really and you still usually get plenty of air trapped in by the time you button it back up and still need to bleed it out.

It doesn't seem like a blown head gasket would prevent you from getting heat. I mean I understand the air pocket theory but you would also be loosing coolant and having to refill, wouldn't you?
 

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For older cars I used to have an adapter where I could hook up a garden hose to one of the heater core lines to flush it out, usually just put some scrap hose on the other end and ran it into a bucket. Not much pressure there really and you still usually get plenty of air trapped in by the time you button it back up and still need to bleed it out.

It doesn't seem like a blown head gasket would prevent you from getting heat. I mean I understand the air pocket theory but you would also be loosing coolant and having to refill, wouldn't you?
Yes, usually. But I think it was explained to me that you don't necessarily have to have coolant leaking out at the same time you have air leaking in... But in reality I don't think that is my issue. I still want to confirm it by testing the coolant for exhaust contamination.

Today has been fine... haven't had an issue with it. But Sunday I did. It's so weird how intermittent it is.

Sometimes if it's really cold outside (like 20 or below) and I turn the heat on, I can watch my temp gauge drop... I mean it makes sense... the heater core is basically a small radiator and blowing a fan over it is going to cool off the engine coolant. But it happens so quickly and it never gets back up to full operating temperature... this is one situation that points me back to the thermostat... but I have no way of ordering a MOPAR OEM thermostat for this vehicle anymore.
 

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It does sound an awful lot like a sticking thermostat type of issue, but you've tried so many different ones already. I have had plenty of bad brand-new t-stats over the years though. Any completely different brand ones available you could try that you haven't yet?

It would help if you could get a drawing or illustration how how the cooling system flow works. I don't know what the second stat is for. If you could fully trace the path you should be able to narrow it down. Any vague possibility that a hose is hooked up to the wrong spot allowing t-stat bypass and over-cooling?
 
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