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Discussion Starter #1
Well, I took all the basic steps to get the heat back. Flushed the heater core in both directions several times, replaced as much coolant as I could without removing knock sensors (dead frozen). The coolant is relatively clean. Replaced the heater hose tee and restrictor while there. After a couple of heating/cooling cycles, added coolant to the expansion tank so it is higher than the COLD mark on it by one inch.

The heat did come back for a couple of days... Gone again... The core could get clogged again, but I doubt it. Can there still be some air in the system? Does not it bleed itself after a few heating/cooling cycles?
 

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Are one,or both of the heater hoses hot after warming to operating temps?
 

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Well, I took all the basic steps to get the heat back. Flushed the heater core in both directions several times, replaced as much coolant as I could without removing knock sensors (dead frozen). The coolant is relatively clean.

The heat did come back for a couple of days... Gone again... The core could get clogged again, but I doubt it. Can there still be some air in the system? Does not it bleed itself after a few heating/cooling cycles?
maybe some debris clogged the heater core again since you initially had heat after the flush process...but now don't have good heat. Not being able to remove the KS means you still have not drained all the old stuff out. If you can't get KS out you could try some "cooling system cleaner/flush" product. Drain as best you can and back flush heater core again. Fill with distilled water only and repeat draining system a few times using just distilled water after some drive cycles until the water comes out clear. Drain and then fill with a 50/50 mix of distilled water and coolant. Basically do multiple drains since you can't get the KS out to do a through job first time

If you had air in the system you would overheat...the system does not "self bleed"

using tap water (has minerals) builds up deposits in cooling system and engine....if that is what you had been doing previously
 

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Discussion Starter #4
maybe some debris clogged the heater core again since you initially had heat after the flush process...but now don't have good heat. Not being able to remove the KS means you still have not drained all the old stuff out. If you can't get KS out you could try some "cooling system cleaner/flush" product. Drain as best you can and back flush heater core again. Fill with distilled water only and repeat draining system a few times using just distilled water after some drive cycles until the water comes out clear. Drain and then fill with a 50/50 mix of distilled water and coolant. Basically do multiple drains since you can't get the KS out to do a through job first time

If you had air in the system you would overheat...the system does not "self bleed"

using tap water (has minerals) builds up deposits in cooling system and engine....if that is what you had been doing previously
I have done exactly what you had described. The engine has been well-maintained, so I really doubt the coolant is dirty and could clog the heater core within days. GM coolant supplement was used before, but since then the system was flushed many times.

I watch the temps and they are usually around 179. The thermostat operates properly as well. I heard of coolant filters, but am really tired of playing with the cooling system. Looks like I will spend yet another winter without heat. :(
 

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Discussion Starter #5
Are one,or both of the heater hoses hot after warming to operating temps?
The both hoses are hot, so there is a flow through the core, but not necessarily through entire core.
 

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Another possibility is that the hot/cold "blend" door is in operable due to a vacuum line,and/or HVAC control issue. Possible door blocked by debris,or linkage/control issue....
 

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Another possibility is that the hot/cold "blend" door is in operable due to a vacuum line,and/or HVAC control issue. Possible door blocked by debris,or linkage/control issue....
^^^this. If the return line is hot, there is flow through the core. The problem must be inside. Stuck door, bad actuator, control line leak, etc. just start at the head and work your way to the blend door and check each item for proper function. You'll find it.
 

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There can still be flow from inlet to outlet with most of core totally clogged resulting in little,to no actual heat in cabin.
 

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You should check the head unit, and the temp sensor inside the dash. If the interior temp sensor is malfunctioning, it will not operate the heat door in the plenum.
 

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Discussion Starter #10
You should check the head unit, and the temp sensor inside the dash. If the interior temp sensor is malfunctioning, it will not operate the heat door in the plenum.
I believe the air mix door operates properly, based on the variation of the heat I get at different settings.
 

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You have the choice of clogged core, inop/stuck heat door/actuator, interior temp sensor, debris on the outside of the core, and head unit. You can access the door from the drip pan, and once the drip pan is removed, it is relatively easy to replace the heater core.
 

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Discussion Starter #12
You have the choice of clogged core, inop/stuck heat door/actuator, interior temp sensor, debris on the outside of the core, and head unit. You can access the door from the drip pan, and once the drip pan is removed, it is relatively easy to replace the heater core.
After I flushed the heater core on my 1991 Seville, it started to leak. So, I was prepared to replace the core of the Fleetwood after the flush, but it did not leak. I can replace it, but if clogging IS the problem, the chances are the new core will get clogged soon after. I try to eliminate all other possibilities before I do that.
 

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I believe the air mix door operates properly, based on the variation of the heat I get at different settings.
so you say I believe !!! so you have XRAY vision ?

as other members have stated both hoses hot on the heater core that means the temp door.............

this system on my 96 impala you caddy hot coolant flows thru the core all the time , the engine is on.

possible linkage is broken or debris preventing the door to move.

not sure how the caddy HVAC system is controlled exactly ....but both hoses hot means heater core is working...the heater air output temp should be 140F when the temp is set to max heat.

engine vacuum line on engine could have a leak also , that specifically feeds the HVAC .. that line has had failures with other owners.
 

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Discussion Starter #14 (Edited)
so you say I believe !!! so you have XRAY vision ?

as other members have stated both hoses hot on the heater core that means the temp door.............

this system on my 96 impala you caddy hot coolant flows thru the core all the time , the engine is on.

possible linkage is broken or debris preventing the door to move.

not sure how the caddy HVAC system is controlled exactly ....but both hoses hot means heater core is working...the heater air output temp should be 140F when the temp is set to max heat.

engine vacuum line on engine could have a leak also , that specifically feeds the HVAC .. that line has had failures with other owners.
That's NOT what I said... Here what I said and it makes sense, IMHO.
"I believe the air mix door operates properly, based on the variation of the heat I get at different settings."
Of course, a visual inspection is the best. I can do that at some point.
 

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That's NOT what I said... Here what I said and it makes sense, IMHO.
"I believe the air mix door operates properly, based on the variation of the heat I get at different settings."
Of course, a visual inspection is the best. I can do that at some point.
variation of the heat not very clear because what is the air temp also the settings where it provides no heat , some heat ? post the air temps in what position the controls are set.

as I stated this is NOT a coolant flow problem.... both heater hoses hot like the upper radiator hose means coolant system good.

this a computer controlled HVAC ? could be that is the problem .. impala has manual system so very basic controls ..
 

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Discussion Starter #16 (Edited)
variation of the heat not very clear because what is the air temp also the settings where it provides no heat , some heat ? post the air temps in what position the controls are set.

as I stated this is NOT a coolant flow problem.... both heater hoses hot like the upper radiator hose means coolant system good.

this a computer controlled HVAC ? could be that is the problem .. impala has manual system so very basic controls ..
Cannot the both hoses be hot while most of the core clogged? Just imagine the coolant does not go through all the passages, but takes a short cut. Correct me if I have a wrong idea of the internals of the heater core.

I set it at 90 and I get some heat, I set it at 60 and I get much less heat. That makes me believe the air mix door do move. Again, nothing like a visual inspection, but the door is not the primary suspect. I still believe the system has some air in it.
 

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Cannot the both hoses be hot while most of the core clogged? Just imagine the coolant does not go through all the passages, but takes a short cut. Correct me if I have a wrong idea of the internals of the heater core.

I set it at 90 and I get some heat, I set it at 60 and I get much less heat. That's make me believe the air mix door do move. Again, nothing like a visual inspection, but the door is not the primary suspect. I still believe the system has some air in it.
so you have a computer controlled HVAC system well that may require computer replacing.. fred might have one .. one trick which may work is remove battery power to vehicle this may reset the HVAC computer ... I had to do this on my 2000 GM truck others also with this HVAC issue..

I have troubleshooted these on impala and other gm vehicles air in system will cause the hoses to be both NOT hot .. bleed the goose neck again see if it is solid flow ...put the temp setting to max measure the air temp ..
 

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Cannot the both hoses be hot while most of the core clogged? Just imagine the coolant does not go through all the passages, but takes a short cut. Correct me if I have a wrong idea of the internals of the heater core.

I set it at 90 and I get some heat, I set it at 60 and I get much less heat. That makes me believe the air mix door do move. Again, nothing like a visual inspection, but the door is not the primary suspect. I still believe the system has some air in it.
The heater cor could definitely be partially or mostly clogged.I went through this on my 94 Caprice.Both the inlet/outlet were evenly hot,restricted.Here's a couple pics I took before and after I cut open the heater core. This is the original I replaced.Had 81k miles on it when I replaced it with a new GM core.Been one year and heat has been great since.I run a stock 180 t-stat as well. Jim
 

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Discussion Starter #19 (Edited)
The heater cor could definitely be partially or mostly clogged.I went through this on my 94 Caprice.Both the inlet/outlet were evenly hot,restricted.Here's a couple pics I took before and after I cut open the heater core. This is the original I replaced.Had 81k miles on it when I replaced it with a new GM core.Been one year and heat has been great since.I run a stock 180 t-stat as well. Jim
Nice pictures. Did it also leak from the connection of the side tanks with the core? Usually, all-metal heater cores do not leak. Though possible, I think it is quite unlikely that the heater core got clogged again just in a day or so. I still suspect some air in the system.
 

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No it had no leaks when I changed it out HUF. Just lack of good heat was the issue.I also changed out the hoses,stat,pressure tank/cap,etc...
 
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