Uh-oh, heat not working

I put the heat on for the first time this year (96 caprice), the air coming out gets the slightest bit lukewarm, just enough to not be the cold outside air, but defininitely not strong heat. Checked coolant level in the recovery tank, it's OK, and temp guage is about 1/4 above the C under normal driving. No heater core leaks or coolant on the floor or anything like that. Any ideas as to what might cause this? Thx.

Entrapped air, plugged heater core, or water valve failure.

Check the heater hoses under the hood once the engine is warm. If only one is hot, or if they are only barely warm, there is inadequate coolant flow through the core. You can try to flush the core with clear water if you suspect clogging.

Where is the water valve located? Is that the same as the vacuum controlled heater control valve on the older cars that was under the hood by the AC?

it could aslo be the thermostat ive seen that happen a couple of times and every time we just changed that part and boom nice heat

Where is the water valve located? Is that the same as the vacuum controlled heater control valve on the older cars that was under the hood by the AC?

your vehicle has even on the hotest days coolant flowing thru the indash mounted heater core...this heater core for some reason gets plugged with crap....I've been there done that before...so when I replace my dexcool every 3years approx...I make damm sure I flush out That heater core and on all my other vehicles the same ...when my vehicle was new back in 96 the heat was poor...those damm GM sealant tabs plugged it up...no problems with heat now ...maybe too hot usually run on 50% ...

use of air pressure is a good way after the heater core flushing to get every thing in there out...

how often do you do this coolant replacement ? do you do it or some repair shop? I doubt the repair shop will do it takes more time ...

yep take off your heater hoses at the firewall and shove a garden hose on one of th e heater core tubes and then the other go back and forth til you got nothing but clean water coming out in both directions then do it some more for good measure thenput it back together and top off your coolant and if still nothing thermostat time

One more thing I noticed is that the temp. guage only goes up to about 1/4 above the C. Should it be higher than that? ALso, when stuck in traffic it tends to climb toward the middle until you start driving again, then it quickly goes back to 1/4 above C. What should the guage read during normal driving?

One more thing I noticed is that the temp. guage only goes up to about 1/4 above the C. Should it be higher than that? ALso, when stuck in traffic it tends to climb toward the middle until you start driving again, then it quickly goes back to 1/4 above C. What should the guage read during normal driving?


this is normal 1/4 to 1/3 thats it....like I said my heater will burn your feet...if the heater core is clean....this with the 1/4 temp reading...this never changed since nov 1995...

one more for you to look at is a weak rad cap that is releasing presure before the rated 15 psi Pressure Rating (SAE Range 14-18 psi) will not let the temp stay at the normal temp of the Thermostat thats in the car. a weak Thermostat also will give low temp.

one more for you to look at is a weak rad cap that is releasing presure before the rated 15 psi Pressure Rating (SAE Range 14-18 psi) will not let the temp stay at the normal temp of the Thermostat thats in the car. a weak Thermostat also will give low temp.


this system is 15psi...if the 15 psi is not available you use the 14psi..If you use 16-18 psi. this will blow out the radiator...

the only reason you use this pressure cap is to prevent boiling at temps above 212deg F...once the coolant boils the engine overheats due to air in the WATER pump...can't pump air...

another member suggested bleeding the system this is a possible cause...as an air bubble could be traped in the heater core though on this vehicle I have never seen it..but on other vehicles it is common..

because he has the correct temp readings I believe this is the typical plugged heater core very common with these vehicles..

this system is 15psi...if the 15 psi is not available you use the 14psi..If you use 16-18 psi. this will blow out the radiator...

the only reason you use this pressure cap is to prevent boiling at temps above 212deg F...once the coolant boils the engine overheats due to air in the WATER pump...can't pump air...

another member suggested bleeding the system this is a possible cause...as an air bubble could be traped in the heater core though on this vehicle I have never seen it..but on other vehicles it is common..

because he has the correct temp readings I believe this is the typical plugged heater core very common with these vehicles..
j cAT FYI: the % of coolant in the system determines when it will freeze/boil. the rad cap psi is set to release coolant at it's 15 psi and let coolant back in to the closed system when the system cools down. if the cap did stick it will blow out the weakest point. a weak rad cap will not give the proper pis for the heater core to run at the optimun heat output for under -30 temps. all good infro on the heat problem to date.

463, by radiator cap, I am assuming you're talking about the cap on the recovery tank, no cap on the actual radiator on 96's? If the coolant level in the tank is low would it affect heater performance?I felt the heater hoses to see if they're cooler than the lower rad. hose, but all 3 seemed to be just mildly warm (maybe because it's 35 degrees outside today??)compared to the upper rad. hose which I think was hotter, will have to check again.If the thermostat was running too cool, would the temp. guage also show too cool?

463, by radiator cap, I am assuming you're talking about the cap on the recovery tank, no cap on the actual radiator on 96's? If the coolant level in the tank is low would it affect heater performance?I felt the heater hoses to see if they're cooler than the lower rad. hose, but all 3 seemed to be just mildly warm (maybe because it's 35 degrees outside today??)compared to the upper rad. hose which I think was hotter, will have to check again.If the thermostat was running too cool, would the temp. guage also show too cool?

your problem is with the heater core...the heater core hoses need be hot...the thermostat with this vehicle works very different than most engines..hot coolant will continually flow thru the heater core...the thermostat is special for this engine and it is possile someone installed the wrong type of thermostat...the temp should be 180deg F...

the correct thermostat costs more and some install the wrong type..
once again with your temp readings it is most likely the heater core..


with this system 50% minimum dexcool coolant with distilled water only..I use 65% dexcool with distilled water...this will protect the metals from damage and reduce any restrictions to flow of coolant thru the engine...better heat transfer to radiator etc..

one thing you must Be careful of is do not spill any coolant on the front cover of the engine as directly below the thermostat housing is the distributor,which if coolant gets into it will not be good...many have damaged there distributor by spilling coolant on it..

as I stated before this flushing of the heater core is required at every coolant change,,,especially if you live where it is cold....

there is no magic fix...it you do this work you will have to get DIRTY..
GOOD LUCK

One more thing, as I prev. mentioned if you run at idle for a few minutes the temp. needle starts heading toward the middle. I tried doing that to see if the heat would get stronger and the heat did not improve very much. Does this mean it's not thermostat related?

One more thing, as I prev. mentioned if you run at idle for a few minutes the temp. needle starts heading toward the middle. I tried doing that to see if the heat would get stronger and the heat did not improve very much. Does this mean it's not thermostat related?

that is also a very normal condition ....when the ac is off and idlling for a period of time the temp gauge will climb to about 50% area then one of the electric fans will come on that,, is if your engine has the fans.... some do not depending on the type of cooling system that was install when the vehicle was produced...the HD tow pkg has the non electric fan clutch ..

this as described condition points to the heater core because with a higher coolant temp the heater is still not hot ,,,also the heater hoses are the same temp as the radiator hoses if not then this to indicates lack of flow...

Not to confuse the issue, but I played around with it a little today and here's another thing I found, both on the Vent and Floor setting. With the fan on the lowest setting, I can feel heat coming out, almost feels like the full heater. When I turn the fan higher, such as 2 or 3, you can feel the heat drain out and after about 10 or 15 seconds it is blowing cold air (not completely cold, but defininitely not very hot). It goes back to heat when I put the fan back to the lowest speed. Thus, I have almost full heat on the lowest fan setting but almost none on the 2 3 or 4 fan setting.

Not to confuse the issue, but I played around with it a little today and here's another thing I found, both on the Vent and Floor setting. With the fan on the lowest setting, I can feel heat coming out, almost feels like the full heater. When I turn the fan higher, such as 2 or 3, you can feel the heat drain out and after about 10 or 15 seconds it is blowing cold air (not completely cold, but defininitely not very hot). It goes back to heat when I put the fan back to the lowest speed. Thus, I have almost full heat on the lowest fan setting but almost none on the 2 3 or 4 fan setting.


well now I think your just screwing with me...

back flush the heater core

Just disconnect both heater hoses. Put a water hose in one and flush until it runs clear. As previously stated both hoses should be hot when up to temperature.

My 96 Caprice heater has made my crazy for 2 years. I have done all that has been suggested, flush engine, heater core, tank twice. The liquid flows well. The liquid temp is right where it belongs which brings me to the last suggestion and probable cause; the equipment valve (baffle flapper if you will) under the dash is not operating well.
I am looking for help in understanding what is under there for me to fix. Can't find a book or person who can tell me where to start.

Look at the heater control valve in the panel where you turn the heater on. My Malibu has a rotary dial where you turn on the heat my Silverado has the same type of unit. It has a number of vacuum hoses attached to it. Make sure you have vacuum going to the firewall connection. Then check for vacuum to the valve and make sure the vacuum goes through the valve. On the side of the heater case should be a vacuum motor just a vacuum pot and rod that moves the blend door. Make sure this unit is working.
I've purchased a unit from a scrap yard before. I used a vacuum pump to be sure it worked. Watch them pull it then you will know how to install this unit.

My 96 Caprice heater has made my crazy for 2 years. I have done all that has been suggested, flush engine, heater core, tank twice. The liquid flows well. The liquid temp is right where it belongs which brings me to the last suggestion and probable cause; the equipment valve (baffle flapper if you will) under the dash is not operating well.
I am looking for help in understanding what is under there for me to fix. Can't find a book or person who can tell me where to start.

are the 2 heater core hoses hot ?

exactly what thermostat did you use ...manufacturer and model #

what engine is this ?

are the 2 heater core hoses hot ?

exactly what thermostat did you use ...manufacturer and model #

what engine is this ?
The heater hoses are hot and the thermostat works fine. There is heat coming out of the heater and it is hot but not enough volume. You have to turn the adjustment knob up all the way. It used to put out so much it would drive you out but it is a struggle to get enough heated volume to do the windshield and heater. The AC works fine in the summer. If I knew more on how the da.. system worked I would say "it is some kind of air blender door problem".

I had heater hoses off and flushed both engine once, heater core 3 times ran free and cleaned fill tank 3 times. Ran coolant through core and into a bucket until clean. I'd bet the ranch plugs are not the problem. I had a pack rat and mouse problem in 2008 so I had to clean out the blower and duct a few times. So far the blower works fine but is it possible something is keeping the tempering door/flap/or whatever from working properly?
Where can I find out what is under the dash and how the heater system works?:confused:

The heater hoses are hot and the thermostat works fine. There is heat coming out of the heater and it is hot but not enough volume. You have to turn the adjustment knob up all the way. It used to put out so much it would drive you out but it is a struggle to get enough heated volume to do the windshield and heater. The AC works fine in the summer. If I knew more on how the da.. system worked I would say "it is some kind of air blender door problem".

I had heater hoses off and flushed both engine once, heater core 3 times ran free and cleaned fill tank 3 times. Ran coolant through core and into a bucket until clean. I'd bet the ranch plugs are not the problem. I had a pack rat and mouse problem in 2008 so I had to clean out the blower and duct a few times. So far the blower works fine but is it possible something is keeping the tempering door/flap/or whatever from working properly?
Where can I find out what is under the dash and how the heater system works?:confused:

this is a better description of whats going on....send me your email address.. I have the diagram showing the temp doors inside the air ducting..since you have rodents around you need to install some rat wire where the air enters the air ducting but not at the top of the hood area..

removal of the air intake screens at the top hood area will reveal down on the firewall where the blower is mounted openings that rodents can easily enter..looking in the hole passengerside of the air intake about 12inches down..

I had some acorns get to my blower one time and could not figure out how that occured since I put filter material and carefully sealed the top air intake...thats when I found the hole as described above..

that air duct must have debris in it or they may have chewed up something...

Hey thanks it looks like you hit on it. Sorry for not being more specific at the start. You can email at [email protected]
Looking forward to your email.

Update from before - I replaced the water pump bec. it was leaking, had heater core flushed, but I am still having same problem with the heat being barely warm and/or cold intermittently. One thing I noticed when I got home and checked the hoses is that both heater hoses are warm near the w/p before the little black plastic T tube, but on the other side of the tube near the firewall the lower one is warm and the upper one is cooler. Any more suggestions? Thx.

Also, where is the heater control valve located on a 96 4.3 Liter V8 engine? All I see in the entire heater hose line is a black plastic T fitting near the coolant tank that is in the lower hose and goes to the coolant tank, nothing else in the whole line. The local parts store showed me a round device with 3 water hose connections and a vacuum fitting, but I don't see it anywhere. THx.

http://www.ebay.com/ Look in the dash where you turn the rotary dial.
item 170363559374 This controls vacuum to the doors make sure the supply is working.
1993 item 170348842831
The engine has to be up to full temperature and you will notice some difference.

Also, where is the heater control valve located on a 96 4.3 Liter V8 engine? All I see in the entire heater hose line is a black plastic T fitting near the coolant tank that is in the lower hose and goes to the coolant tank, nothing else in the whole line. The local parts store showed me a round device with 3 water hose connections and a vacuum fitting, but I don't see it anywhere. THx.


this system has no coolant flow valve...hot coolant flows continuously thru the heater core...if you have little heat it is usually the heater core plugged, there is air in the system, or the temperture door control /door is not working correctly inside of the air box...

95 Caprice 4.3 engine. Heater core replaced, water pump replaced, radiator replaced, thermostat replaced (195). I flushed the system several times, still little or no heat inside. The temperature gauge reads 1/4 while driving, 1/2 when idle after 10 minutes.
I had my brother-in-law shoot the hoses with a temp gun. It showed 160 to 180 near the water pump up to the restrictor on the bottom hose and up to the t on the top hose. Above these two it’s any where from 95 to 120.
I was told that the flow restrictor is to keep the heater core from too much pressure. If this is clogged or not working properly it will act as if the heater core is clogged and really isn't. It may be just trickling a little in at a time. I've ordered my part and will put the new one on in the morning.
I see where it's at, and found a couple places that told you how to remove one with out cutting the hose. I don't know what one looks like on the inside, I'm guessing it's a baffle of some sort that prevents pressure building at the heater core. The new one doesn't look anything like the stock OEM model, oh well. Let's cross our fingers.

Does any of this make sense?

HVAC Heater Control Valve -- Flow Restrictor
http://www.partsgeek.com/catalog/1996/chevrolet/caprice/climate_control/heater_valve.html

95 Caprice 4.3 engine. Heater core replaced, water pump replaced, radiator replaced, thermostat replaced (195). I flushed the system several times, still little or no heat inside. The temperature gauge reads 1/4 while driving, 1/2 when idle after 10 minutes.
I had my brother-in-law shoot the hoses with a temp gun. It showed 160 to 180 near the water pump up to the restrictor on the bottom hose and up to the t on the top hose. Above these two it’s any where from 95 to 120.
I was told that the flow restrictor is to keep the heater core from too much pressure. If this is clogged or not working properly it will act as if the heater core is clogged and really isn't. It may be just trickling a little in at a time. I've ordered my part and will put the new one on in the morning.
I see where it's at, and found a couple places that told you how to remove one with out cutting the hose. I don't know what one looks like on the inside, I'm guessing it's a baffle of some sort that prevents pressure building at the heater core. The new one doesn't look anything like the stock OEM model, oh well. Let's cross our fingers.

Does any of this make sense?

HVAC Heater Control Valve -- Flow Restrictor
http://www.partsgeek.com/catalog/1996/chevrolet/caprice/climate_control/heater_valve.html

so all these parts are new ? installed like yesterday ?

If so I would remove the heater hoses at the engine, then using a water hose of 10-20 psi see if it flows / then revesre the flow.

If this is good then you either have air in the system , bleeder at goose neck , or the door in the ac/vent chamber is not moving stuck or a vacuum issue with this control..

this vehicle has no flow control valves ..when it is 100deg f out the cooling ac is on full blast the heater core has full hot coolant flow...

you must use the correct thermostat. it must be the CORRECT design. should be 180 deg f. ................. 195 f is too high...


fill the system with coolant and with tank cap OFF run until at proper temp.. should go to the 1/4 of temp guage..

my 96 impala had heater core issues many years ago GM SEALANT TABS , these restricted my heater core..after flushing using the water hose no more problems...I do this at every coolant replacement ..my feet get burn't it is a good heater system..