How to stop hot air from engine compartment?

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Steve Mcbean

Steve Mcbean

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My car has no factory A/C, the heat is turned to off, and I'm pretty sure there's firewall insulation, yet it feels like lots of heat is passing thru the vents underneath. How can I keep heat from passing thru the vents? Or is it just radiant heat, not air in the vents?
 
What year make and model?
I doubt you have firewall insulation. Maybe whatever is under the carpet, which isnt much.
May need to install Dynamat or something similar. It will keep the heat, and noise down.
 
You just need to look around very closely at the firewall inside and outside. Sounds like there is a leak somewhere.
 
Also look at the steering column seal. My knees were getting blasted by hot air from a slot in the steering column tube. A bit of research here told me it was likely a seal at the base of the column (inside the engine compartment) Some duct tape over the slot temporarily/permanently fixed the problem.
 
missing linc said:
Heater temperature control cable probably stuck and not closing the door inside the heater box fully.
Click to expand...
or the heater valve in the engine compartment is not closing and letting the hot water flow though the heater core
 
kursplat said:
or the heater valve in the engine compartment is not closing and letting the hot water flow though the heater core
Click to expand...

Joey4speed said:
What year make and model?
I doubt you have firewall insulation. Maybe whatever is under the carpet, which isnt much.
May need to install Dynamat or something similar. It will keep the heat, and noise down.
Click to expand...

Would I need to remove the dash too, or just stick to the carpet?
 
You can turn the fan blade around so it blows the air outward through the radiator and out of the engine compartment...











:poke::lol:...
 
Make sure the heater flaps are closing correctly, also get an infrared temp gun, you should be able to narrow it down with that
 
There is a seal at the back edge of the hood. Maybe its letting hot air in somehow
 
Steve Mcbean said:
My car has no factory A/C, the heat is turned to off, and I'm pretty sure there's firewall insulation, yet it feels like lots of heat is passing thru the vents underneath. How can I keep heat from passing thru the vents? Or is it just radiant heat, not air in the vents?
Click to expand...
If its coming out the heater vents, first thing to check is if the heater controls are shutting them off properly. They're just flaps mechanically controlled by the cables.
upload_2020-5-15_9-11-4.png


One here.
upload_2020-5-15_9-17-29.png


With the fresh air vents (doors in foot well) open, no air to speak of should be coming out the heater or defroster vents.
upload_2020-5-15_9-13-11.png


Yes there should be firewall insulation as well as seals for every opening.
The firewall insulation is a black hardboard with yellow fiberglass held in place by large plastic pins.
Here is a replacement set that DMT used to make.
upload_2020-5-15_9-4-27.png
 
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toolmanmike said:
I don't know much about 71 Demons but is there a heater valve under the hood? My 70 Swinger doesn't have one. Just a cable operated door in the heater case under the dash.
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You're right Mike.
From the '71 Plymouth FSM.
upload_2020-5-15_9-44-52.png
 
512Stroker said:
Sound like a great idea.
Could you provide some details on how you did this. Maybe some pic's?
Thanks
Click to expand...
You can disconnect the heater hoses at the engine and loop a hose connecting the two or disconnect them at the firewall and hook them together with a splice nipple. Some cars have 2 different sizes of hose so you will need the proper nipple for that. Usually 5/8 and 3/4".

hose splice.jpg
 
If you put a bag of weed on the manifold and take it for a ride you'll be able to rule out if its coming from the engine compartment. Keep the windows up. Trump 2020
 
flingdingo said:
Also look at the steering column seal. My knees were getting blasted by hot air from a slot in the steering column tube. A bit of research here told me it was likely a seal at the base of the column (inside the engine compartment) Some duct tape over the slot temporarily/permanently fixed the problem.
Click to expand...
I had that going on in my 66. The lower column seal was gone and dang, that drivers side manifold is pretty close. The column near my knee was hot to the touch.
 
kursplat said:
or the heater valve in the engine compartment is not closing and letting the hot water flow though the heater core
Click to expand...
basic heat/defrost only builds don't have a water cut off. A lot of owners install a hand operated ball gate valve in a heater hose for the warm weather months.
 
RedFish said:
basic heat/defrost only builds don't have a water cut off. A lot of owners install a hand operated ball gate valve in a heater hose for the warm weather months.
Click to expand...
Or a pair of needle nose vice grips on the hose to test. LOL
 
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