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Discussion Starter · #1 ·
Gotta get this resolved before it really gets cold & starts snowing! As topic says, my 91 Trooper (2.6L) has poor heat. Heater core is flowing good (took hoses off and ran water hose into bottom inlet and it freely flows out of top outlet so no blockage). I think this is right - it flows in the bottom to top direction?

What exactly does that "heater control valve" that the cold-hot temp lever moves inside the cab do? You know, the thing that's connected by rods to your temp selector that actually moves (turns) that's on the air controls box near the firewall near the gas pedal when you move the selector from cold to hot? I always thought it controlled the coolant flow into the heater core but it doesn't. When I did my water hose test, water flows no matter if the selector was on hot or cold - no difference in flow at all.

But the hot/cold lever does work - on cold I get ambient temp air, on hot it does warm up but it's not anywhere as hot as it should be. The valve is moving it's full range and the coolant temp is hot (about 1/3 of the way up on the gauge, maybe a bit more - more than enough to get decently hot air. So I'm thinking that valve diverts the air flow through the heater core rather than coolant flow, and somehow my air isn't fully being diverted through the heater core? What's the fix?

Another reason (besides my test) it seems logical now that there isn't a valve that controls coolant flow through the heater core (apparently the heater core always has coolant flowing through it). Looking at the coolant flow diagram, it seems most of the water returning back into the bottom of the radiator is coming from the heater core, and there's only that skinny 3/8" hose that's the bypass, so it seems you'd have big problems if the heater core got clogged?

So my coolant is getting hot enough, and I think it's circulating through my heater core just fine, so I must be having problems with the air not diverting fully through the heater core, right? Any help would be much appreciated!
 

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My 2.6 1991 Trooper had the same issue with the heater, warm in the winter but not hot and I would cover the front with a piece of card board which helped but still not enough on real cold days. I always thought it was either thermostat or some thing in the controls. I was also having intermittent cooling problems so at the end of the summer I put in a new radiator. That cured the cooling issue but I found out that winter it had also cured the heater problem nice consistent hot air evidently the radiator was restricting the coolant flow enough to effect the heater. To make a long story short you might want the check the condition of the radiator and make sure you are getting a full flow. DAVE
 

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If the temp control lever does not change the water flow volume through the heater core then the water valve within the core is bad. Since you are not getting full heat it's not opening all the way- it will flow water but not as much as it should. My Trooper had exactly the same symptoms, a new heater core solved the problem. JLEMOND has new ones, but they are pricey. If I had to do it again i would have the local radiator shop build a core that would fit(was quoted $50), then add a separate cable-activated water valve under the hood. While you have the coolant drained go ahead & have the radiator cleaned out- outofrshell is correct, the more flow through the radiator the better the heat will be.
 

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Discussion Starter · #4 ·
Ok, so apparently the temp control lever should control the water flow volume through the heater core after all. My radiator is fairly new so then it must be a bad water valve.

So, now my question is, how do I exchange the heater core? I have a parts Trooper, and tried getting the core out of it, but haven't been successful - what's the secret? It's been awhile since I tried and can't recall exact details of why I failed. Seems I had trouble figuring out what's holding it in and what all I had to remove to get to it. I was accessing it from the drivers side.
 

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To remove the heater core you basically have to dismantle the entire bottom portion of your dash. The plastic surround has to be split apart and the heater core removed.

Have you looked to see if your thermostat is working? I'd try replacing it before you go through the hassle of tearing down your dash. If the valve is operable and you don't have that sweet smell in your cab, it should be fine.
 

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Using search, you should find threads here detailing the removal process of the heater core.
 

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Discussion Starter · #7 ·
Have you looked to see if your thermostat is working? I'd try replacing it before you go through the hassle of tearing down your dash. If the valve is operable and you don't have that sweet smell in your cab, it should be fine.
Thanks for all the advice so far.

The heater core isn't leaking, and I really don't look forward to changing out the heater core! On a cold start, my temp gauge starts climbing and goes sorta high (over the halfway point) and I can see the thermostat open, 'cause the temp suddenly will drop to a bit below the halfway point and stay there. So I believe the thermostat is working. I do notice that the heat is better when the temp gauge is higher.

Looking at the service manual diagram, it appears that if the majority of the coolant flowing back into the bottom of the radiator is coming from the heater core, and there's only a small bypass hose that provides this coolant if the flow from the heater core is stopped (i.e. when the valve is closed). So I'm still confused as to how it gets enough flow if you shut off the flow through the heater core, but I'll take everyone's word for it that that's what this heater control valve is supposed to do.

So from my testing it appears that my valve is stuck open. To me it seems to be stuck wide open and not halfway, I say this because my testing with even a small trickle of water from the water hose seemed to flow through the core just fine, and when I turned up the pressure to flush it out, it flowed good, so it doesn't seem to me that my valve is stuck halfway. But, I'm not getting adequate heat, so I'm taking the advice that it must be stuck halfway open.

I had this lack of heat problem with the old radiator, which I replaced with a newer radiator from a donor Trooper. The PO of the donor Trooper claimed that radiator was fairly new and it looks it. So it's possible that I still have a flow problem through the radiator (i.e. fairly new radiator isn't all that new), but it's more unlikely.
 

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thrashercharged said:
Looking at the service manual diagram, it appears that if the majority of the coolant flowing back into the bottom of the radiator is coming from the heater core, and there's only a small bypass hose that provides this coolant if the flow from the heater core is stopped (i.e. when the valve is closed).
That's incorrect. Firstly, coolant does not flow "back into the bottom of the radiator is coming from the heater core". Coolant flows from the upper radiator downward to the lower radiator. As you can see, the heater coolant routing has its own circuit, to a point, so that a minimal amount of radiator cooled fluid enters the heater core when the heater is activated. It's probably the valve. If you go back and look at your manual, you should see the hot water valve. You should also see the bypass line before the valve. If the valve goes belly up or accumulates build up, the coolant will route through the bypass. It does any how, however, it must reroute coolant in the event of the valve/heater core clogging/shutting down.
 

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Discussion Starter · #9 ·
Yeah you're right - flowing back into the bottom of the radiator doesn't make any sense does it - the water pump draws from the radiator lower hose. The manual I have is a Chiltons, I'll have to look at it again but I'm fairly certain it doesn't even show the hot water valve.
 

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thrashercharged said:
Yeah you're right - flowing back into the bottom of the radiator doesn't make any sense does it - the water pump draws from the radiator lower hose. The manual I have is a Chiltons, I'll have to look at it again but I'm fairly certain it doesn't even show the hot water valve.
Gimme a minute and I'll load it up for you.
 

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Discussion Starter · #12 ·
Ah - thanks for the diagram! That's much better than the one I have (which is a Haynes, not a Chilton as I previously stated.) So the heater core does feed the water pump, it's just not the the main feed (the lower radiator hose is), it's like an alternate feed, so I can see now if it's blocked and water has to flow through the bypass, it's no big deal - the water pump still gets enough water to cool the engine.

My test results still confuse me though. Driving the truck at normal operating temp and moving the temp lever does make the air temp go from cold to lukewarm, so evidently the hot water valve is doing something to change the flow. But when I remove the heater hoses and run water through the heater core with a water hose, moving the temp lever doesn't change the water flow at all, it just keeps flowing.

From the responses, I either have a water valve that isn't opening completely, or a radiator that's partially plugged and not flowing freely enough to feed the heater core.

What side of the thermostat is the feed to the heater core coming off of? The engine side or the radiator side? I'm wondering if perhaps my thermostat isn't opening enough and somehow impeding flow to the core? Just wondering if there's a third possibility for the lukewarm heat.
 

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Have you checked the water valve link rod and the air mix door adjustments?
 

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I'd cut to the chase and get a replacement 192* (for the factory 180*) either at a parts store or here: http://www.motoradusa.com/catalog.php?C ... N+VIN%3A+E They have OE, High Flow, and Fail-Safe types. That would let you know really quickly where the problem is. I've never been impressed with a 180 for heating whether the radiator, etc is new or old.
 

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Discussion Starter · #15 ·
Have you checked the water valve link rod and the air mix door adjustments?
The water valve link is hooked up and seems to be adjusted right (i.e. turning the valve from min to max). I don't know anything about the air mix door - can you tell me how to adjust it?

This is my son's car and he's got it at college right now (had it back for Thanksgiving when we were trying to get the heater to work) so he'll have to suffer with mediocre to no heat until he comes back for Christmas in a few weeks. I think I'll try a new thermostat first unless adjusting the air mix door is pretty simple to do. Thanks for everyone's advice and help.

We got our first snow today, took me 2 hours driving my 40 mile commute in my car - passed 13 cars in ditches. Worst commute ever, snow was coming down faster than plows could keep up, I could barely keep on the road doing 20 mph, had to stop twice to clear snow off the headlights. Snow came earlier than I'd expected - I gotta get my '91 Trooper on the road again (2.8L rod knock, swapping engine with my donor with the frame that's rusted away - and I do mean totally rusted away as in the body is keeping the front and rear together!) and the '02 I just got with the 4L30e that needs rebuilt. Too many projects, so little time...
 

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Pay close attention to the first paragraph and illustration. These two items are on the upper driver side of the heater box. To quickly orient yourself to them, move the heater slide mechanism to and fro and you will see the air mix door mechanism and actuator rod move.

 

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Discussion Starter · #17 ·
Thanks for the diagrams - I'll be visiting my son this Sunday so I'll have a chance to look at it in the parking lot - can't do much serious work on it but I can mess with the linkages.

I'm not sure I understand the diagrams and instructions in the Mode and temp cable section. In (3) it says to connect the cable with the temperature lever and heater? lever set in the HOT position, then fix the outer tube with a cable clip? I'm not able to read it all due to the blurred words but it seems this section might be pertinent to my problem. What are the blurred words in the last sentence of (3)? And the bottom diagram looks important - what's it showing?

Thanks - Tom
 

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I don't recall the blurred words. I have posted a clear version of this before. You'll just need to use search to find it. You're problem has only to do with the section I directed you to if it's heater control related.
 

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Discussion Starter · #19 ·
Well it's getting close to winter and this Trooper still has lukewarm heat and my boy is complaining (actually it's probably his GF complaining so now it's a priority to him). I've searched the archives for heater core removal and have only found references to them being a PITA to do, some say you have to rip out the entire dash, others say you can slide the HVAC back until the pipes clear the firewall and then slide the core out the drivers side, so I'm taking this approach.

Here's a pic of the donor:


1. The big circle is the heater core. The arrows point to the pipes. Do I simply take the plastic side cover off and the core will then slide out the drivers side?
2. The small circle is the valve, right? I assume the bottom pipe is the inlet since the valve is on that pipe?
3. I've flushed my core several times with a garden hose and it seems to flow fine, but I assume the valve must be partially plugged since I only have lukewarm heat (relatively new radiator and temp gauge stays at about the 1/4 mark so I think the radiator is fine.) Any way I can service this valve and make sure it's flowing while it's in the car so I don't need to do this swap with the donor?
4. What else is holding the HVAC box in place? Just the linkage cables? How many are there? I only see the temp control cable going to the passenger side of the box. Where are the others I need to remove to get the box out?

Thanks,
Tom
 

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You don't have to pull the dash or the entire heater to swap the heater core. You have to remove the A/C evaporator box then there are 4 nuts that hold the heater box in place. Remove the heater hoses in the engine bay, then 2 screws that hold the heater core to the heater box. You have to get the bellcrank turned out of the way and then you have to remove the arm for the heater core water valve rod... Not a big deal, you should be able to get it out in 30 minutes or less.
 
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