Mark Houlahan
Brand Manager, Mustang Monthly
February 1, 2013
Photos By: Courtesy of National Parts Depot
Shown here is the typical weld-in cowl patch, as seen from under the dash and installed on the passenger side (the heater box inlet butts up against the opening).

The well-travelled vintage Mustang owner knows that the hobby's biggest four-letter curse word is r-u-s-t. Rust has ravaged its fair share of vintage Mustang body panels and one of the more problematic areas is another four-letter word that brings chills to Mustang owner's spines—the cowl.

The '65-'68 Mustang's cowl design is certainly not one of Ford's better ideas. The cowl panel is made up of an upper and lower sheetmetal stamping that is welded together and welded to the firewall as well as the windshield framework. Unlike today's coated metals and robotic painting processes, the cowls in '65-'68 Mustangs were simple sheetmetal parts spot welded together and given a coat of paint, certainly not the most rust preventative measures. Combined with the sealed design, it was a rust issue just waiting to happen.

Starting in 1969, Ford made the cowl area a bit more accessible via a removable grille panel, mainly for servicing the wiper motor and transmission, which also made it easy to keep the lower cowl clean of debris. This debris is what causes the rust issues in the '65-'68 design.

While Ford did design a drainage trough on each side of the cowl that exited the cowl sides into the fender area, the drains easily get clogged with pine needles, tree leaves, dirt, and other debris that enters the cowl vent opening. This debris traps moisture in and against the steel of the lower cowl panel. The combination of air and moisture over time initiates the metal's transformation into rust. As the rust worsens, causing penetration of the cowl panel around the cowl vent's "hat," the ensuing perforation allows future water ingress (natural rains, car wash water, etc.) into the passenger compartment, soaking the carpet and causing further rust issues with the floor pans, the Mustang's next biggest rust issue.

If you're one of the lucky few to have a garage-kept vintage Mustang or perhaps lived in a southern and dry climate, then you most likely have nothing to worry about. However, for the rest of us, cowl vent rust and leaks are a real problem. Some may say that the only proper repair is to cut out the rusty cowl portions and weld in patches or a new cowl. While we agree with this wholeheartedly, we also understand that not everyone has the budget for a complete cowl replacement. Not to mention some cowls may have minimal rust while others look like Swiss cheese. So for a cowl with just a couple of small holes, a complete replacement is a bit of overkill.

Thankfully there are several solutions that vary in price, practicality, and the amount of labor involved. Read on as we go through each solution and the pros and cons of each.

If you suspect you have a cowl leak, a bucket of water or a stream of water from a hose will help diagnose the situation and pinpoint where the leak is coming from. Just don't mistake a leaking windshield gasket for a cowl leak. It is often best to gut the underside of the dash (gauges, wiring, wiper assembly, heater box, etc.) so you can get a clear view of the complete cowl to determine where any issues lay. If your car has a nice paint finish and you don't wish to repaint the cowl and/or pull the windshield, some shops will install the cowl patches from inside the car, but the welding/sealing is more difficult in this manner and, as such, be prepared to pay a little more. Speaking of cost, we've outlined the parts cost and typical labor costs for each option below.

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