View Full Version : Is there a fix for water leaking in cowl vent?

06-23-2003, 12:10 AM
I noticed the other day when it was pouring rain like mad, I saw a drip then a stream coming from the passenger side firewall. I had this happen in my 89 SC as well. What is the best way to eliminate this problem before it stArts to rust out my floor (brings back memories of the old Mustang leaky cowls!!!)

Any ideas?

thanks again,


06-23-2003, 10:24 AM
Under your cowl panels is the air intake for the heater, it's surrounded by a small vertical wall that rises above the cowl it's attached to. This wall is supposed to keep water out of the plenum but it's not very tall. The water should drain off to the passenger side of the cowl through a small gap between the fender & cowl and down behind the fender to the ground.
If leaves/debris have piled up over the years at that gap then it's possible for the water to back up and the level rise high enough to overflow into the air intake and gather in the heater plenum. It's ok for a little water to get into the plenum because there is a drain built onto it for times like this, but if the drain gets stopped up then you can have problems.
There is also a foam gasket that seals the plenum to the underside of the cowl, it can deteriorate from age and water can get between it and the plenum and drip down the outer shell of the plenum inside the car. Leaves can also pile up on the built-in grating of the intake and shed water towards the gasket.

Soooo...pull your passengerside cowl panel, look at the gap between the fender & cowl for debris that might prevent runoff of rainwater.
Physically look at the air intake flange (the little wall around it) to see if it's rusted through at the joint where it sits on the cowl (hope not!).
If the flange is ok, run a little water onto the cowl and see how well it runs off or whether it gathers & pools.
Check your drain tube for the plenum, it's a small plastic tube that sticks out through the firewall approx 6-7 inches below the A/C connections, pokes out about 1/2" or so, you'll know it when you see it. Try probing it with a piece of wire to see if it's stopped up.

Hope this helps, pics available if ya need 'em,