Cabin heat issue
Thread Starter
4th Gear
Joined: Jul 2020
Posts: 4
Likes: 0
Cabin heat issue
I have a 1975 coupe I just love. (Second C3) I am getting very hot air coming thru the vents ONLY after driving for a while, leaving the vehicle for a while then driving again! Doesn't happen on first drive of the day. I disconnected the heater core and the problem still persisted. The flooring has been insulated completely, but the heat is coming thru the floor, side & center vents! AC helps a little, but air is still very warm. This happens tops on, tops off, windows up, windows down. I have been to 4 different corvette shops, (including a "leading" corvette dealer) no one can figure out the issue let alone fix it.
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
Is there a horsecollar foam seal between transmission and floor about even with firewall?
i didn’t even know one existed til i seen mine and repositioned it..still get small amount through e brake handle slot
i didn’t even know one existed til i seen mine and repositioned it..still get small amount through e brake handle slot
Instructor
Joined: Jan 2010
Posts: 129
Likes: 4
From: Perth western Australia
I have the same problem with my 79, now I leave the hood popped open (close hood slowly and let rest on latches)
This lets the heat from the engine bay escape and not go into the cabin. My fellow club members pick me up
on not having the hood closed but NO heat.
Try it you will be surprised.
Andy
This lets the heat from the engine bay escape and not go into the cabin. My fellow club members pick me up
on not having the hood closed but NO heat.
Try it you will be surprised.
Andy
Le Mans Master
Joined: Apr 2008
Posts: 9,435
Likes: 239
From: Powassan ON
I have the same problem with my 79, now I leave the hood popped open (close hood slowly and let rest on latches)
This lets the heat from the engine bay escape and not go into the cabin. My fellow club members pick me up
on not having the hood closed but NO heat.
Try it you will be surprised.
Andy
This lets the heat from the engine bay escape and not go into the cabin. My fellow club members pick me up
on not having the hood closed but NO heat.
Try it you will be surprised.
Andy
of the heater box. “L” shaped, pass side
install a heater core shut off or plug the pump outlet.
Thread Starter
4th Gear
Joined: Jul 2020
Posts: 4
Likes: 0
The issue of the hot air is while driving. Doesn't matter if I let the engine cool down.
The heater core was completely by-passed and it did not solve the problem. I "believe" there is a problem under the dash. Leaking vacuum line, door that doesn't open/close????
Anymore ideas?
The heater core was completely by-passed and it did not solve the problem. I "believe" there is a problem under the dash. Leaking vacuum line, door that doesn't open/close????
Anymore ideas?
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Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
I'm focusing on these clues:
Two ideas:
1. When you disconnected the heater core, did you drain the coolant? Is the core completely bypassed (short loop on the engine, or plugged)? If not, perhaps you are getting heat soak when sitting, and the then hot core is heating the air for a while. If the hot air persists for hours of driving, it's probably not that, but hot air may be entering the heater box through the missing insulation near the heater core inlet/outlet.
2. You said you brought it to four (4!) Corvette specialists. Did any of them adjust the timing to bring it back to factory specs? If so, your timing is almost certainly retarded from optimal, and your car is running hotter than it should. Can you shoot an IR temp gun at the upper radiator hose after running for a while, and let us know what it reads?
1. When you disconnected the heater core, did you drain the coolant? Is the core completely bypassed (short loop on the engine, or plugged)? If not, perhaps you are getting heat soak when sitting, and the then hot core is heating the air for a while. If the hot air persists for hours of driving, it's probably not that, but hot air may be entering the heater box through the missing insulation near the heater core inlet/outlet.
2. You said you brought it to four (4!) Corvette specialists. Did any of them adjust the timing to bring it back to factory specs? If so, your timing is almost certainly retarded from optimal, and your car is running hotter than it should. Can you shoot an IR temp gun at the upper radiator hose after running for a while, and let us know what it reads?
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
2. You said you brought it to four (4!) Corvette specialists. Did any of them adjust the timing to bring it back to factory specs? If so, your timing is almost certainly retarded from optimal, and your car is running hotter than it should. Can you shoot an IR temp gun at the upper radiator hose after running for a while, and let us know what it reads?
Thread Starter
4th Gear
Joined: Jul 2020
Posts: 4
Likes: 0
When I disconnected the heater core it was leaking, so I doubt any coolant was left in it. Yes, I just put in a short loop back to the engine.
The engine does not seem to be running hot. It rarely gets above 200 degrees on the temp gage, even with the air conditioning on high. I will have the timing checked just in case.
The last "mechanic" broke the passenger side kick plate, so I am assuming he checked to see if the fresh air intake was stuck but I'll verify.
The engine does not seem to be running hot. It rarely gets above 200 degrees on the temp gage, even with the air conditioning on high. I will have the timing checked just in case.
The last "mechanic" broke the passenger side kick plate, so I am assuming he checked to see if the fresh air intake was stuck but I'll verify.
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
When I disconnected the heater core it was leaking, so I doubt any coolant was left in it. Yes, I just put in a short loop back to the engine.
The engine does not seem to be running hot. It rarely gets above 200 degrees on the temp gage, even with the air conditioning on high. I will have the timing checked just in case.
The last "mechanic" broke the passenger side kick plate, so I am assuming he checked to see if the fresh air intake was stuck but I'll verify.
The engine does not seem to be running hot. It rarely gets above 200 degrees on the temp gage, even with the air conditioning on high. I will have the timing checked just in case.
The last "mechanic" broke the passenger side kick plate, so I am assuming he checked to see if the fresh air intake was stuck but I'll verify.
Please do check the fresh air intake, and confirm the temp gauge with an infrared temp gun. Your timing should be 36 degrees total mechanical advance at 2800-3000 rpm (no additional advance at higher RPM). But if you aren't checking this yourself, please let us know what the mechanic says. If he says something like "initial timing is 6 degrees BTDC, ported vacuum to the vac advance, just like the manual says", that'll be part of your problem, but easy to fix.
EDIT: You might want to read through this thread, too.
https://www.corvetteforum.com/forums...e-79-w-ac.html
Last edited by Bikespace; Jul 27, 2020 at 08:48 PM.
