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Discussion Starter #1 (Edited)
I have been struggling to figure out my "warm air" issue. 68 gto, car runs a normal temp of 190. After a bit of driving--like 20-25 min, I get warm (hot) air coming through the heat vent even when the heater is turned off. Removing fuse to see if a short and it still blows warm air. Any Ideas?
 

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How is the hood to cowl seal, or is it missing? If all of that hot air from under the hood can get past the seal, it will be forced down into the cowl vent at speed. And if your heater flapper doors don't seal as well as they used to then you get hot air all the time when going down the road. I've seen it before, just add or replace the hood seal and the difference is like night and day.
 

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Discussion Starter #4
69 goatee. Looks like the hood/cowl seal is new. or close to it--no cracks, but i do get hot air as you said when going down the road when car is running at temp. None when sitting still...so you may be on to something, but don't know what.
 

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If the plenum doors close all the way and the seals are good, you should get no flow until you activate the heater control. The cable ends tend to break at the plastic mounting points, so the control acts normal, but the cable housing moves and not the blend air door. Get under the dash with a flashlight and work the controls and see what's up. Also, the bellcrank at the control head can break or bend, causing the same problem. These cars were designed to last ten years, not 40+, so it's normal for some of these small parts to deteriorate.
 

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Discussion Starter #6 (Edited)
69 goatee...just looking on the web and saw a photo of another 68 engine compartment...noticed that my hood to cowl seal goes straight across and not in the holes where they are intended..actually it is on the medal piece that connects the cowl with the firewall..a little lower than the photo- now,I am thinking the person I got it from, did not install it correctly--net all the hood cowl pre holes are visible and no seal around them ...socould be the issue...as we do get that warm air in the car when driving...will get some photo or directions on how it should be installed..hard to find. thanks for the help...will keep you posted.
 

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I agree with Geetee on the door parts and cables. Also you didn't say if it is an A/C car or not. A/C cars have a heater shut-off valve that blocks water from the heater core when temp is set to cool. Non-A/C cars don't have this valve (I think), so hot water is always flowing through the heater core. So, if the doors aren't shutting, then air from the cowl could be forced through the heater system. I have seen everything from leaves, sticks, trash and even a dead mouse stuck in the heater plenums, holding them open.
 

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Discussion Starter #8
non A/c car.. i will try the hood cowl seal...i found that it is completely missing. the previous owner put a seal on..but it is not in the spot for the hood cowl...it is much closer to the firewall and does not wrap around the entire hood...will let you know...trying that first.
thanks for all the help
 
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