Firewall ducts - and engine fumes - 1966

[my66cruiser]

Good afternoon,

Do the two air ducts that can be seen under the hood on both the left and right side near the top of the firewall only go to the big vents under the dash above your feet? Or do they lead elsewhere too?

The big vents above the driver's and passenger's feet are manually controlled by the levers on the dash. Thanks.

It would seem that once the engine warms up they let in hot (and sometimes exhaust fumes) air from the engine compartment. I have a cracked exhaust manifold, which I repair from time to time so this is why I am asking.

[Harley Eaton]

There could be some confusion regarding what you refer to. On each side near the hinge and coming out of the firewall are water drains for the cowl area. The air inlets are on top of the cowl, a series of long slots. Air entering through these slots supply fresh air into the cabin.

[my66cruiser]

Hi Harley,

I think I was confused. I knew that the cowl (two rows of slots) provided air to the cabin but I wondered where the footwell vents got their air from - I guess they get air from the cowl as well based on your answer. Thanks.

So the two 3.5" x 2" (oblong looking) openings on each side of the firewall are water drains - interesting but I wonder if that was a good design or not. So if I take a garden hose and pour water into the cowl, the water will exit through the two ducts in the engine compartment? I am not going to do this, just a question.

Since they are all somewhat interconnected, fumes from the engine compartment can enter the two oblong ducts and conceivably get into the passenger compartment through the cowl I would think unless the air pressure when you're driving prevents this.

As usual, thanks for your help Harley.

[Harley Eaton]

Do you have a shop manual?? If you do, look in there to find your answers. If you don't have a shop manual, GET ONE. You will find that all the air for the heater, ventilation and air conditioning enters the cabin at the same location. The rubber ducts for the water drains are designed to let the water out, but not let fumes in.,

[sseebart]

There are plenty of other opportunities for fumes to get into the car. When I got my 64, the steering column boot was completely shot, the seal for the accelerator linkage had fallen out and the seal for the brake linkage was missing.

Any one of those openings (especially the steering boot) are big enough to let in fume. I know--the car also came with a leaky master cylinder, which was dripping on the left exhaust manifold; I had smoke billowing into the car when I first got it running.

~Steve

[my66cruiser]

Thank you for your answers Harley and sseebart. And Harley, I don't have the shop manual yet. Every time I go to buy one I check this forum first and get a quick answer. I will need the manual soon though.

One issue with my car is the passenger exhaust manifold is cracked. I repair it using something called Pyro Putty 2400 which should last a long time, but for some reason the repair fails and then you smell some fumes and hear the tick...tick...tick sound of an exhaust leak.

So when I smell fumes I know I have to repair the manifold again. I know this is kind of a pathetic way to get along but replacing the exhaust manifold is not an option for me right now. That'll get done when the motor needs to get rebuilt which won't be for a long time.

[my66cruiser]

Hi folks,

I ordered and replaced the two cowl vent ducts - which were practically nonexistent in my car from heat and deterioration. So all I had left were the the two big openings. It was an easy job that required a stubby Philips screwdriver. My old clamps were in good shape so I reused them. What I was happy to see was that the new ducts angle downward and are tapered at the end. So that water can get out but next to no fumes can get in. The new ducts appear to be of some silicone rubber material but I am not 100% sure.

Of course one should address the root problem and correct any fumes from coming from the motor, but that is sometimes easier said than done.

I repaired my cracked exhaust manifold again - this time I let the mixture cure for 48 hours at room temperature instead of starting the vehicle to fast cure from the heat. We'll see how long it lasts this time.