DIY Radiator Cowl for the NA Mazda Miata MX-5


As Spring begins the transition into Summer, thousands of cars are awakening from their Winter slumber, escaping the cocoons of their garages, and venturing forth into the warmth of sunshine and clear blue skies. I have such a vehicle. Well, two. One is currenty hardparked on jackstands at the moment, but oh well, that is #projectcarlife. The car in question is my 1996 Mazda Miata MX-5. As the weather gets warmer, I find myself driving the little convertible more and more (it doesn’t hurt that it gets great gas mileage), but there are some issues (of course there is!) that have been catching my attention.

Crazy world, lotta smells

Ask any owner of a NA/NB Miata and they will all tell you that at some point in your ownership, if there is a fluid in the car, eventually you will smell it. As I am driving the car more frequently, I am noticing a faint smell of coolant, but no leaks and the coolant tank is remaining constant. I replaced the hoses with full set of silicone hoses from HPS (that reminds me, I need to write that article too!) with all new clamps and there isn’t a drop anywhere on garage floor. After much mental wrangling, I discovered that it was the radiator cap, got a new one, problem solved. With that issue sorted, it did help focus my attention on improving the cooling situation with the car. When I bought it, the splash pan was missing. After reading up a bit, I learned that the splash pan does help create a low pressure zone behind the radiator, helping air to pass through it, so I purchased one and installed it.

Now that I got the bottom sorted out, I looked down and noticed that the top of the cowl area doesn’t do that great of a job of keeping the air routed to the radiator. Air will take any avenue it can when it meets resistance. Since I have created a channel on the bottom that helps force air through the radiator, it doesn’t have anywhere else to go. On the top however, there is a gap between the cowl of the bumper and radiator support. Even with the hood closed there is a bit of a gap where air could escape past the radiator and over the top of it. Now that I have committed myself to this quest of corralling as much incoming air as I can through my radiator, I was going to have to figure out this problem. There are many companies that sells radiator cowls for the NA/NB platform and buying one of those would surely be the easier solution. But c’mon this is Five Five Garage! How cool would it be to make my own?

To The Drawing Board

I firmly believe there is nothing scarier than a man with access to power tools, an idea and too much time on his hands.

I started on the endeavor by making a trip to my local DIY home improvement store. It doesn’t matter which one because they all carry the item I went there to buy, a 12″ x 24″ piece of aluminum sheet metal. It really doesn’t take much more than that. The construction of this piece isn’t that complex, you won’t even need fancy tools.

What you will need is a Sharpie pen and cardboard. Lots and lots of cardboard.

Engineering the Prototype
Cardboard Prototypes
Top: The V1 cardboard prototype, I made it too small. Bottom: The V2 cardboard prototype. Engineering at its finest.

Before you begin hacking and cutting like some mad scientist, you are going to want to break out a ruler, T-square, or whatever measuring device you have on hand and take some measurements. Next, find a piece of cardboard that is close to the dimensions of the measurements you just took. Once you have that, begin transferring your precise measurements to the piece of cardboard, going back and forth between the car and your template, marking any holes and cutouts as necessary. I had to make a second template because I cut the first one too short, and it left a gap at the sides. I made sure that the second one was both wider and longer, having it overlap onto the top of the radiator. Make sure to test the fit of the template repeatedly, it is far easier to tweak the cardboard template and get it right, versus trying to do the same to the sheet metal version.

V2 Cardboard Prototype on car
The V2 during the fitment process. I used a box cutter to cut out the hood latch area and the rubber hood stops.

Once you feel like the template is ready, it is time for the Sharpie and the sheet metal. Square the template with the sheet metal, I advise using masking/painter’s tape to hold the template in position and then carefully begin tracing your template onto the sheet metal.

Tracing the design onto sheet metal
This is the point when things get serious.

After tracing everything over the sheet metal. Double check all of your measurements and ensure that everything is square and marked where it should be. Once you begin cutting, it is the point of no return. You can use tin snips (The sheet metal is thin) or use a Dremel (I did). Be advised, I highly suggest you wear gloves when you begin cutting the sheet metal, it will become razor sharp at the edges and you will end up cutting or nicking yourself easily (ask me how I know).

Boom. Perfection.

Once the shape has been cut out, transfer over your marks for holes that need drilled from the template.

Aluminum cowl with markings transferred.

Drill out your holes and test fit the template. It may need a slight tweaking but if your measurements are on point (and they will be) the piece should drop right in without hassle. After I have everything fitting properly, I added some HVAC aluminum duct tape to seal the top of the cowl to the radiator. Since I have made this for my car, I notice A) I don’t smell coolant much anymore, B) the AC fan doesn’t cycle nearly as much when I use it, and C) the car drives better. Is it all due to my clever engineering? Or is a placebo effect? Who knows?

Get out there and drive!


The finished product
A job well done.