Cabin Air Filter

The Miata cockpit can be a very warm place for various reasons. It is not helped that the outside air vented into the cockpit is heated 15-20 degrees above the ambient outside air.

Several years back I decided to try and cool this air down. I used nearly every trick that I could unearth on the Miata Forums, ensure the heater flap closed fully, close holes in hood with tape, stuff a piece of insulation in the seal between cowl and engine compartment and tape over holes in firewall leading to the windshield cowl area, yet I remained defeated. On my own I thought maybe if I removed the big plastic piece over the inlet for the cabin air I might get some outside air directly in the system. This exposed a big opening directly to the vent system’s squirrel fan covered only with a wide mesh appropriately sized to keep out overweight house cats.

Having had to clean small leaves and pieces of pine straw out of that fan from inside the car a few times in my Miata owning career (major milestone approaching) I thought it would be a good idea to cover that up. The only thing I had handy was a spare 20×20 house HVAC filter. So I cut out a piece of the fiberglass mesh roughly the size of the opening, edged it in some maroon duct tape I had left over from covering the holes in the hood and taped it over the opening.

I change the “cabin air filter” out each time I change the oil which is about every 3 months. Do I breath cleaner air because of this filter, I doubt it, what with all the time I spend with the top down, but it must be doing something judging by how dirty it looks when I swap it out. If you look in the clean filter picture above you can see a bunch of debris to the right of the filter, I don’t think this would have made it into the fan without the filter because of the 2″ vertical wall of the opening (probably designed that way to keep out water), but stuff has made it in there before, probably due some sort of perfect storm scenario, and since I have been using this filter method nothing has made in there yet.