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I suspect partial blockage inside the heater core. Many have back flushed their core,and found it helps....
 

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You'd be able to tell if the blower was not humming at full speed. Common to have rodents sneak in the cowl and take up residence, along with their nesting materials. Easy to drop the blower and clean if you suspect something there. But a clogged heater is first choice. Reading other guys' accounts it's important to keep hose pressure low.
 

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Here's a pic of the inside of my son's heater core from his 94 ... and he had a touch of heat.

"OMG" that looks like the worst sickness I have ever seen! How many more out there are like this? As I type I am replacing the heater core in my 96 due to ZERO heat, though I believe my issues is vacuum I still found a bunch of crap during the flush procedure. New engine, new water pump, new thermostat, hoses are mint and a new B Cool radiator. Removing the heater core I also took one of the end tanks off, quite rusty but no where near as bad as this one pictured.
 

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No heat!

Like many Caprice/Impala owners the day has arrived that I have a heat issue with my car. Bit of background. A pristine 96 Impala that during the last 6 or 7 years I have replaced everything on this car. Engine, transmission, rear end, suspension, interior, glass, body and even a custom "B Cool" radiator built to accommodate the T56. I think my big problem is for the past 10 years or more the car has only been on the road during summer. Maybe 750 miles per year and only used the heat once that I recall.

It was shortly after the car was restored that I first noticed no heat. I think my issue is two fold, heater core and secondly a vacuum problem. When I turn the knob for heat I don't hear the door opening, I think I use to hear it? Secondly I drained everything yesterday and flushed the core, I did remove a lot of trash, disgusting. However, still no heat. Being I had a factory AC Delco heater core I thought "why not", so I tackled the job!

Being 65 years young, overweight and the body not wanting to be placed in weird positions the job is not that easy.

Removing the front passenger seat does make life so so so simple! Removing the tray that covers the heater core is another issue. Those two rear screws (5 & 6) will cause you to swear! You can't see them and if you have a fair sized hand you can't feel them! The only way I could see them is with the wife's small mirror. Who put them there? I used a 1/4" flex drive with a 7/32". Screws 1 through 4 are a breeze when laying on your back looking up.

I took a a couple of pictures so you would get an idea of what your getting into. With the use of a 1/4" flex driver the job will be much easier, don't get me wrong it still will cause you to sear a bit. The older you are the cramps will be worse. With the seat out I cover the entire passenger side floor with a couple of nice soft blankets. Feet up on the rear seat, body in the tray and looking up!
 

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Heater core cover

I have another picture that you might find helpful when you attack the job. You will notice the heater core that I am using is a NOS GM core. I was lucky to have this in my stock of goodies. The rear two screws will not go back in!!!
 

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Just came in for the evening, enough is enough! Last night I removed the passenger seat, sill trim and A post trim. Now that I am about done I did not have to remove the sill or A post trim, didn't even have to pull the carpet back.

Removing the seat and laying blankets over the studs is a priority. Made life so much easier, resting the feet on the rear seat and stretched out. A nice drop cord and the wife small mirror was also a big help in locating what I could not see.

The 1/4" flex drive is without question a must and much easier than using a swivel joint (at least I think so). There was nothing so tight that I could not remove it using the 1/4" flex drive, still had a regular 1/4" drive with me. A 1/4" 7/32" socket, small 1/4" extension could come in handy, Philips screwdriver, deep well 10 MM socket and a 10 MM wrench so to remove the firewall brace so you can remove the lower tray. I am thinking this is all you need for inside the car. I did attach the two under hood hoses.

My new NOS core is now in place, both retainers are also. I will not close the cockpit up until I test the car out, just in case I need to start chasing vacuum lines.

Tomorrow morning I will start by tightening down the hose clamps and adding fresh coolant. Will test drive and bleed. If no heat I will start another project.

I do hope this information and pictures might help someone out there. Remember do not change your heater core when children are around!

Larry
 

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Lots of ways to flush. Some use a garden hose, but be careful ... water pressure in a house hose can be 40-80 psi ... and that's NOT ok. I've always attached two long lines to the core (while in the car), filled it with water (and the hoses), set my compressor to 10 psi and blasted the water and cleaner (let it soak) through from both ends ... maybe 10 times till the water flows through easily. I hold my finger on the outlet side hose (switching back and forth) till just before I hit the compressor blast. But look back at the picture ... it didn't last long. My son's problem was rust scale inside the engine ... it just wouldn't stop building up.
 

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An easy way to tell if you have a blocked core (or hose) is to turn OFF the heater and fan and warm up the engine. Stay close. Wait for the hose going into the heater core to get warm (it's generally the lower line). With the heater and fan off, the heat in the hose will simply run through the core and back into the water pump with very little heat loss. If the two hoses are not "roughly" the same temperature ... something is blocked. At some point the bottom hose will become very hot ... if the upper hose is not as hot ... major blockage. You can also disconnect the outlet side of the core and watch for coolant flow, but unless you know what the flow is supposed to be, you can be deceived by any flow at all.
 

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Hoi guys, the heater of my '91 Caprice doesn't get as warm as it used to be. Temperature of the car is normal. So what can be the cause?
As touched on throughout the thread, you most likely have a blocked Heater core and should try to Flush it out first. If that does not work, then it may be time to replace it if you just can't get it clean. If it is not leaking and if you have a radiator repair shop local to you, it may be worth the effort to have them clean it as I don't like aftermarket Heater cores.

As Deputy mentioned, take the time to pull the passenger seat as you will be "less miserable" in doing this job. But if you have little kids in the area, be sure to remove them from earshot as things tend to get a little "frustrating" and the tools and expletives start to fly. Imagine laying on your back, reaching up and behind you with metal Studs sticking in your back "Gotdam FutherMucking piece of......" ;);)

Lots of ways to flush. Some use a garden hose, but be careful ... water pressure in a house hose can be 40-80 psi ... and that's NOT ok. I've always attached two long lines to the core (while in the car), filled it with water (and the hoses), set my compressor to 10 psi and blasted the water and cleaner (let it soak) through from both ends ... maybe 10 times till the water flows through easily. I hold my finger on the outlet side hose (switching back and forth) till just before I hit the compressor blast. But look back at the picture ... it didn't last long. My son's problem was rust scale inside the engine ... it just wouldn't stop building up.
Pretty much how I flushed mine except I bumped the pressure to about 20 PSI. I left the hoses connected at the FW and disconnected those hose down the line that provided a place to easily fill and Blow out the HC in both directions and did this a numerous times....I'm probably overdue on doing this again.

OP - Not as familiar with the 91 setup as the LT1/L99 in the 94-96 models but the concept is the same as you need to get the crud out of the core. However, not much sense in doing this unless you also take the time to Flush out the entire system. Whatever crud is in the Core, is also throughout the system and will just get pushed thru the Core again unless you remove as much as possible.

It can be a lot of extra work but to do this properly, you really need to drain the rad, whatever reservoir your car has, Pull the Knock sensors or drain Plugs in the block and FLUSH it ALL out. If you don't, then you pretty much guarantee that you will have the Heater core Plugged up again. Expect to do this again soon if the system has been neglected which will help clear residual crud that the first flush missed. Top off with a 50/50 mix of green and Distilled Water and bleed the system. Also a good idea to inspect/replace any Hoses that look suspect as well as REPLACE and Plastic parts that may be on the hoses along with a new T-Stat while the system is apart. On the 94-96 setups, there are 2 Plastic Parts that SHOULD be replaced if you go this far to flush the system and again not sure what your 91 (LO5 Engine?) setup has but something to look into when you do this.
 

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Well the Impala is just about back together again. Wish I could say I have heat, but not really. I have bled the system at least five time now, I bleed until there is no air. Drive the car 6-10 miles and bleed again, darn if I don't get some air.

As I mentioned this is a new engine, B Cool radiator and heater core, Do you think I have one of those air blockages that is going to fight me? After I bled it last time I am thinking the air seems a tad warmer? Might be my dreams too!

When I put everything back together I did not reinstall the two rear screws, in the above picture that would be 5 & 6. The drain tube goes through the firewall and the other four screws hold the bottom tray very snuggly.

Tomorrow I am driving about 40 miles to a show so I will bleed her at least twice tomorrow.

Larry
 

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Here is a trick that works amazingly well. I discovered it by accident, but would not be surprised if other have also discovered this. I've drained coolant out of these engines so many times, I'm a pro ... and can do it on a new carpet and not get it wet (ha, just kidding, but close).

Fill the engine with coolant. Don't bother starting it. Use a coolant pressure tester to pump up the system to 12-13 psi at the reservoir. As you bring up the pressure, use this opportunity to check for leaks, fix them ... beats the heck out of doing it when you run the engine waiting for pressure and leaks and dealing with everything being really, really, hot.

As well, sometime early on after a few pumps (1-2 psi), open the bleeder at the thermostat and let that air out. When fluid comes out, close it. Way more effective than trying to bleed by gravity (no pressure). Take it on up to 12-13 psi slowly (once all leaks are cleared).

Now ... release the pressure quickly at the pressure pump, however that is done on your pump unit, but do it in quick bursts, maybe 4-6 psi at a time. You will hear a very audible gurgling sound ... that is the air being forced through the system to the high point (bleeder and reservoir).

The fluid level in the reservoir will drop. Fill it back up to the fill line. Repeat this process as many times as it takes till you no longer hear the gurgling sound and the reservoir level stabilizes ... and don't forget to let the air out at the bleeder early in each pumping cycle (at low pressure).

When done, do one more cycle all the way to 16 psi (including the bleeder step) and let it sit for a few minutes and check for leaks. Release that and start up the engine. I still check for air a couple of times after running the engine, but only to make sure I didn't miss a gurgle cycle and to fill the reservoir after things settle.

For all you serious techies. This works on the principle of expanding gas. Coolant does not compress at all, but air does, big time. As the air expands when we quickly release the pressure, it moves violently ... thus working it's way up to the bleeder and reservoir. You could probably accomplish the same effect by slamming the engine with a huge sledge hammer, but this is far easier. Just takes a few minutes.

Good luck.
 

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Here is a trick that works amazingly well. I discovered it by accident, but would not be surprised if other have also discovered this. I've drained coolant out of these engines so many times, I'm a pro ... and can do it on a new carpet and not get it wet (ha, just kidding, but close).

Fill the engine with coolant. Don't bother starting it. Use a coolant pressure tester to pump up the system to 12-13 psi at the reservoir. As you bring up the pressure, use this opportunity to check for leaks, fix them ... beats the heck out of doing it when you run the engine waiting for pressure and leaks and dealing with everything being really, really, hot.

As well, sometime early on after a few pumps (1-2 psi), open the bleeder at the thermostat and let that air out. When fluid comes out, close it. Way more effective than trying to bleed by gravity (no pressure). Take it on up to 12-13 psi slowly (once all leaks are cleared).

Now ... release the pressure quickly at the pressure pump, however that is done on your pump unit, but do it in quick bursts, maybe 4-6 psi at a time. You will hear a very audible gurgling sound ... that is the air being forced through the system to the high point (bleeder and reservoir).

The fluid level in the reservoir will drop. Fill it back up to the fill line. Repeat this process as many times as it takes till you no longer hear the gurgling sound and the reservoir level stabilizes ... and don't forget to let the air out at the bleeder early in each pumping cycle (at low pressure).

When done, do one more cycle all the way to 16 psi (including the bleeder step) and let it sit for a few minutes and check for leaks. Release that and start up the engine. I still check for air a couple of times after running the engine, but only to make sure I didn't miss a gurgle cycle and to fill the reservoir after things settle.

For all you serious techies. This works on the principle of expanding gas. Coolant does not compress at all, but air does, big time. As the air expands when we quickly release the pressure, it moves violently ... thus working it's way up to the bleeder and reservoir. You could probably accomplish the same effect by slamming the engine with a huge sledge hammer, but this is far easier. Just takes a few minutes.

Good luck.


Great information! Like you I have drained the coolant systems on many 9C1s as well as Impalas. There has been one other one in my life that had such a air blockage that it took for ever to bleed. Unlike you I have only "gravity" bled the systems!

Questions: I realize the pressure tester attached to the reservoir, does your have a screw on cap or is it a plug?

Would you be so kind as to recommend a kit?

Thank you so very much for the much needed advise.
Larry
 

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This is available from Stant. Screws onto the reservoir and gives you a standard radiator cap for the pressure tester fitting.

https://dl.dropboxusercontent.com/u/21929029/Stant.JPG

This is the pressure tester (pump) I use ... has a standard radiator connector. Atlas model PT-10.

https://dl.dropboxusercontent.com/u/21929029/Atlas.JPG
Thank you very much, I appreciate your time. It was in the low to mid 60s here in coastal NC today so I had he car out. Drove to a local show and ended up putting 80 miles on the car. Still no heat, but I believe there is light at the end of the tunnel.


I can say for sure it's not the engine, It's not the water pump, it's not the heater core. These things I know for sure, now the rest I am assuming! Someone borrowed my 96 maintenance manuals so I just purchased another set from Flea Bay, should be here by the 24th. Then it's reading time again!
Larry
 

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Deputy ... Trust me on this gurgle trick. I have never had air left in my cooling system doing this. Dozens of times. Before ... my fair share. Running up the pressure without heating the engine is a big plus (still have to do that, of course), but finding leaks when cool ... priceless.
 

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Deputy ... Trust me on this gurgle trick. I have never had air left in my cooling system doing this. Dozens of times. Before ... my fair share. Running up the pressure without heating the engine is a big plus (still have to do that, of course), but finding leaks when cool ... priceless.
An interesting trick for a tricky cooling system. :smile2:
 
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