Condensation in cab - The 1947 - Present Chevrolet & GMC Truck Message Board Network

71 C20 CS · 12-15-2023, 12:02 AM

My cab is getting really wet inside on the roof and windshield. The door seals are new and I checked they’re sealing properly and there’s no leaks, carpet is dry everywhere, but somehow moisture is getting in, there is so much condensation on the roof, it gets really wet, I have to towel it off.

Anyone have any experience with this? I was told by a mechanic to put dynamat on the roof and it will stop, but that sounds odd to me.

GASoline71 · 12-15-2023, 01:08 AM

I'm assuming by your handle that you have a '71 C20. How is the driprail seal? Is it all chipped out and rusted?

I live in western WA and know how wet it can be, and we've had a LOT of rain lately.

Gary

truckster · 12-15-2023, 01:23 AM

Do you have leaves blocking the cowl drain holes under the vents?

Also check the bottom of the windshield, the cowl area, and the firewall for rust.

**dagnabbitt** · 12-15-2023, 01:39 AM

Generally speaking indicates a heater core issue, even in modern vehicles.

GASoline71 · 12-15-2023, 01:53 AM

Oh, and do you have clearance lights on the roof?

Gary

**68 C10 Driver** · 12-15-2023, 01:33 PM

Quote:

Originally Posted by dagnabbitt

Generally speaking indicates a heater core issue, even in modern vehicles.

Good starting point...71 C20 CS, does it smell or even give you that "taste" of anti-freeze when you drive it?

71 C20 CS · 12-15-2023, 10:07 PM

Quote:

Originally Posted by GASoline71

I'm assuming by your handle that you have a '71 C20. How is the driprail seal? Is it all chipped out and rusted?

I live in western WA and know how wet it can be, and we've had a LOT of rain lately.

Gary

The drip rail is in good shape, no rust on the roof.

71 C20 CS · 12-15-2023, 10:09 PM

Quote:

Originally Posted by 68 C10 Driver

Good starting point...71 C20 CS, does it smell or even give you that "taste" of anti-freeze when you drive it?

I don’t think it’s the heater core, no coolant smell or leaks, the cab seems tight I don’t understand where it comes from. Even with a waterproof cover and tarp over it condensation still builds up.

71 C20 CS · 12-15-2023, 10:10 PM

Quote:

Originally Posted by truckster

Do you have leaves blocking the cowl drain holes under the vents?

Also check the bottom of the windshield, the cowl area, and the firewall for rust.

Cowl is free of debris.

**Getter-Done** · 12-15-2023, 10:30 PM

Are the Fresh air vents opened or closed?

Do they have debris or leaves in them?

12-15-2023, 12:02 AM	#1
71 C20 CS Registered User Join Date: May 2021 Location: Seattle Posts: 13	Condensation in cab My cab is getting really wet inside on the roof and windshield. The door seals are new and I checked they’re sealing properly and there’s no leaks, carpet is dry everywhere, but somehow moisture is getting in, there is so much condensation on the roof, it gets really wet, I have to towel it off. Anyone have any experience with this? I was told by a mechanic to put dynamat on the roof and it will stop, but that sounds odd to me.

12-15-2023, 01:23 AM	#3
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,980	Re: Condensation in cab Do you have leaves blocking the cowl drain holes under the vents? Also check the bottom of the windshield, the cowl area, and the firewall for rust. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

12-15-2023, 01:39 AM	#4
dagnabbitt Senior Member Join Date: Dec 2014 Location: Edmonton Alberta Posts: 1,453	Re: Condensation in cab Generally speaking indicates a heater core issue, even in modern vehicles. __________________ DAVE Edmonton, Alberta 1959 Apache 1967 K20 1968 C20 1970 C10 1972 GMC 2500 1981 C10

12-15-2023, 10:30 PM	#10
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 8,441	Re: Condensation in cab Are the Fresh air vents opened or closed? Do they have debris or leaves in them? __________________ ________________________________________________________________________________________ ____________________________________________ 84 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build



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