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Matt J
Matt J, Chevy Technician
Category: Chevy
Satisfied Customers: 1399
Experience:  10+ years automotive tech, 5 years of experience in a GM dealer
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I have a heater problem with a 96 tahoe. Replaced heater core,

Customer Question

I have a heater problem with a 96 tahoe. Replaced heater core, water pump, and thermostat. No heat or limited heat, then take off bypass hose and bleed. Heat starts to run. then after the car has been shut off for a while, no heat again. After it runs for some time, the heat may return but not real hot.
Submitted: 8 years ago.
Category: Chevy
Expert:  Matt J replied 8 years ago.

Hello my name is XXXXX XXXXX I will be more than happy to assist you.


There are only a few things left that can cause your problem.

Heater Control Valve, Blend Door, Blend Door Actuator, or The HVAC Controller.


To start off warm your vehicle up to operating temp 175 - 210 deg...turn the heater on full blast.


Take your hand and feel the heater hoses that go to the heater core at the fire wall.


See diagram.


Does Blue Line A and Blue Line B Feel the same temp?

Does Red Line A and Red Line B Feel the same temp?


Customer: replied 8 years ago.
I have done this. I also have already changed this bypass valve. I did verify that when set to max cold, the bypass valve has vacum and pulls in. Line going to heater is hot and return is not. If I manually pull the return by the waterpump and bleed the line it pumps out water and both hoses get hot. then when put back together is works better as long as the car is running. turn off the car and let it sit and when started the return line is not hot again. Water pump is new and when return is pulled with engine running the return line pumps out coolant and the water pump end does not force coolant back out. I believe the controls are right inside as when the return line gets hot, I have heat. I am not loosing collant that I can see either.
Expert:  Matt J replied 8 years ago.

For what you stated it seems like the heater hoses are backwards. Swap the two heater hoses around, retest, and let me know what happens.




Customer: replied 8 years ago.
The hoses are attached exactly how they are referenced in the drawing you sent. do you still want me to swap them? If so do you swap them before the bypass valve or at the heater core?
Expert:  Matt J replied 8 years ago.
Swap them before the heater control valve.
Customer: replied 8 years ago.
Tried to swap the heater hoses, but they are diferent size and so is the connection on the valve so they couldn't be swapped. I then opened the cap, and ran the engine up to temp. added some collant from the hose swap, and cheked the two heater hoses and they both were warm. When they started ti get hot, i put the cap back on with plenty of collant in the overflow tank. There was some heat in the car, but the guage only read pas the firts mark (half way to normal operating temp. This car has been running cooler for quite some time. An intake manafold was replaced a year or so ago by a dealer and ever since then it seemed to run cooler. I have put 2 thermostats in with the last one coming from the dealer, but there is no diference. We live in northern Maine, so it is cold up here, but my chevy truck runs plenty hot. Maybe I am chasing the wrong issue, maybe it is just that the car doesn't get hot enough. I will accept your answer for my original question and pay you again if you need it to help me figure out why the engine is running cool. Let me know, and i will accept if necesary and then post another question for just pay you again. Let me know!
Expert:  Matt J replied 8 years ago.

We havn't solved your issue yet so I don't feel it would be right for you to pay me yet.


When you added coolant did you add it to the overflow or in the radiator when the engine was running?

Customer: replied 8 years ago.
I added it to both. The overflow had a little in it, but it wasn't full. The engine just seems to run cool. I haven't seen it reach 200 for a long time, even in the summer
Expert:  Matt J replied 8 years ago.

Every thing going on has to do with the thermostat. Coolant is bypassing and not allowing the engine to warm up and not suppling hot enough coolant to the heater core.


I know you replace the thermostat twice, but would still pull it out and do a boil test on it.

stick it in boil water with a thermometer in the water, get the water up to 130 and stick the thermostat in it and watch when it opens. if it opens up below 175 deg then it is bad. If it opens open after 185 deg then it is good.


If the t-stat is good then coolant has to be by passing the seal, bad seal, the seal is not thick enough, or the housing is warped. Since you had a new intake put on there is a chance there was a change in design and the thermostat seal is to thin.


Do you still have the paper work when the intake was replaced. If so look for the part # XXXXX the intake and tell me what it is.

Matt J and other Chevy Specialists are ready to help you
Customer: replied 8 years ago.
Sorry I had no time to check the thermostat yesterday. I agree with you, it has to be around that. I have replaced the thermostat twice since I noticed it was running cooler and both thermostats; including the one I just bought at the dealer last month act the exact same way. I guess maybe the seal is not good, as I will have to look at that closely once it is opened up again. Unfortunately I do not have the part number from the intake change. It happened 2 years ago and I misplaced the reciept. Given the problem has to be around the thermostat, and I haven't had the time to check it fully, I will accept the answer given and open another case with you later if I run into a wall again. Thank you for your help. I wish I could check it out and get back to you right away, but it looks like this weekend before I can get to it.
Expert:  Matt J replied 8 years ago.

If you find any thing out this weekend reply back and let me know, If I am not online the website will send a mesage to my cell phone/PDA and I can log in on my cell or my computer and reply back.

Customer: replied 8 years ago.

Hi Matt


I feel like i am going in circles. I checked the thermostat and seal, both are good. I believe my temp sensor is off as the hoses are getting hot after it warms up. It has been very cold the last few months and so I wasn't getting the engine up to temp when checking the heater hoses. they are both getting hot and are close to the same temp. So i went inside the vehicle and checked a few things. If I have it in the mode that runs air out the vents, and I put on the recyle button, I see the motor in front of the blower turn and the air gets plenty hot. however if I turn it to defrost which i need to do to keep the windows from fogging the motor in front of the blower opens up and the air is just lluke warm which keeps the windows clear but doesn't heat the car. Is the motor in front of the fan working correctly? With outside air of below 0 comming across the heater core, it cools it off prenty quickly and the air gets pretty cool. If i turn the vents back on with the recycle button pushed it gets hot immediately. I am confused. I would think when the temp is turned up the ait should not becomming from the outside or it cools it down. What am i missing??



Expert:  Matt J replied 8 years ago.

Yes and No, when you have it on vents and recycle it will blow the hottest, when you have it on defrost it will blow cooler because the air is coming from the out side and also the ac compressor is kicked on also.


So either it is normal for how cold it is or you have a blend door sticking and the out side cold air so blowing across the heater core and AC evaporator core cooling the air down even more.


For as the blend door being stuck you would normally have the same problem on vent also for a few minutes after you go from defrost and vents

Customer: replied 8 years ago.
So what should happen on the blend door when going from defrost to panel? I look at the one before the blower and it only moves when the recycle button is pushed on and off. Or if I go to defrost it turns too, because recycle isn't used there. the is another motor under the glove box that I checked when I started working on this problem, and it seems to turn when I adjust the heat level dial. Is that the blend door? what about going from defrost to panel, is there another motor that controls this airflow? Could that be part of the problem? How would I check to see if the blend door is sticking? I am not sure how long it takes to get warm again after moving to panel, but it isn't minutes anyway. May take 20 to 30 seconds, I would have to time it to make sure. I feel I am getting close to the issue, but not qite there yet. I know on my 04 silverado, the defrost is hot air and not just warm even when it is coold out. Is there a manual somewhere that explains how these motors work for diferent settings and how to fix them??
Expert:  Matt J replied 8 years ago.

If you change the setting to vents with out hitting the recycle button. Does the vent blow the same temp as the defrost?

Customer: replied 8 years ago.
Yes it does!
Expert:  Matt J replied 8 years ago.

Comparing the 96 Tahoe to your 2004 Silverado won't do you much good. GM did a change in design so the difference my be normal.


Before you start tearing into the dash, Let do one simple test to make sure there is a problem and it is not normal.


On the AC compressor there is a connector by the pulley, disconnect it and see if the air gets hotter (see pic below)


I have to look at a 1996 Tahoe tonight after work, I will check out and see how hot the air gets on the defrost and vents.



Customer: replied 8 years ago.
I pulled the connector to the compressor. I didn't notice any diference. it was quite cold out tonight during testing so it wasn't getting that warm either. It was -15 when testing.
Expert:  Matt J replied 8 years ago.

I did a check on another 96 Tahoe temp out side 15 deg, I had a 15 to 20 deg difference from the defrost to vents. I did not expect that much of a drop.


With you being around -15 deg the will make a sizable difference in how hot your vehicle will blow. If I was in weather that cold I would be blocking off 1/4 to 1/2 of the radiator to keep the air flow down on the radiator so the vehicle get heated up more.


Check the radiator fan with the engine off see if it turns easily with one finger. If it is hard to turn then the fan clutch is bad and that would explain your why you don't get up to temp in the summer also.



Customer: replied 8 years ago.
Thank you for your input. I will block off some of the radiator during these Winter months. I checked the fan clutch. It isn't really hard to turn but there is more resistance than the fan clutch on my silverado. This is the original fan clutch from 1996 with over170,000 miles on it. Should I go ahead and change it? Does the part need to come from a dealer or will an aftermarket one work just fine? Any type to look for?? Sounds like it might help
Expert:  Matt J replied 8 years ago.

If you have to really pull or push on it then yes, I would just block off part of the radiator that should help you get up to a hotter temp giving you more heat.