DIY: Coroplast grill block
This weekend I installed a lower grill block on Swarthy. It was cold out, but I wanted to get something done on the car. I have had the coroplast piece cut out for over a week now, so I figured it was time to finally get it on the car.
First things first though. Some of you may be wondering what a grill block is. A grill block is a mod that blocks some or all of your grill opening off. The purpose of this modification is mainly to improve the aerodynamics of the vehicle. The more aerodynamic it is, the less power required to push it through the air. The less power required to push it through the air, the better fuel economy you get. Another benefit of the modification is that it helps warm your engine up faster by allowing less air through the engine bay. Arguably, you can probably accelerate faster too and have a higher top speed, but thats really not a big deal unless you're drag racing your Mirage.
There must be a downside though, right? Otherwise why wouldn't they do it from the factory? Well, actually Mitsubishi did a pretty good job already of blocking the grill off already. Nearly half of the open area on the lower grill is already blocked off. Here is a before picture of my Mirage. You can see the passenger side of the grill is not actually open very much.
The real downside of this modification is you need to watch your coolant temperature. Blocking off the grill does reduce the amount of air going through the radiator, and thus it reduces the cooling capacity. The more you block off, the more you need to keep an eye on the temperature. If you go too far, you will notice your cooling fan turning on more often. If taken way too far, you could overheat and damage your engine.
So, why block off more than stock? Mostly, to improve aerodynamics further and speed up warm up even more. I've done this on enough vehicles to know that even with a 100% grill block (mail slot and all), I would be completely fine on my short commute to work during winter. I know that if I was going to take a freeway trip, I would need to open up some area. I think the mail slot will be plenty of area to cool year round without any issues, even on the freeway. That may seem like a tiny opening, but you have to remember that the cooling system was designed to run through death valley on a bad day running the A/C. Its MASSIVE overkill for Wisconsin weather. If you do this mod, you will have to tailor it to your own climate.
So, lets get started with the DIY!
First, get yourself a piece of corregated plastic. The stuff I used is about 1/8" (3mm) thick. I used black because it blends in great with the car. You can buy it from Home Depot or a sign shop. I just checked online and Home Depot has this material in a 4'x8' sheet for $20. It looks like this.
I measured the lower grill opening, and cut a rectangle the same size. No need to be super picky. To cut it, I used a drywall square, pencil, and a nice heavy duty scissors. I may have even used my wife's nice kitchen shears, but lets keep that on the down low...
With it cut roughly to size, start shoving it in the grill area and see where you need to trim. You can put in as much effort as you'd like here. I honestly just started cutting to what I thought was good. I trim off a big chunk, test fit, cut again, test fit, cut, rinse, repeat. You'll end up with a piece that looks quite similar to this.
Now that you have it cut out, its time to attach that thingy to the car. To do this, I gathered a myriad of useful tools including a phillips screw driver and two black zip ties (yes, I know its not a myriad, that was a joke).
I decided to use two zip ties to hold the grill block on. The one on the passenger side goes through one of the openings, around the main middle horizontal bar, and back out another opening and then through the holes in the grill block. The other just goes in the open area on the other side. So, I used the screw driver to poke some holes in the grill block.
Now, stick the zip tie in one of the holes of the grill block, and fish it through the grill on the car. I recommend starting with the passenger side as it'll be harder to get the zip tie through. I also recommend leaving the zip tie loose while you work on the other side. Once both are through, pull them tight.
This is what it looks like just walking by.
A bit closer up.
View my fuel log 2015 Mirage DE 1.2 manual: 45.4 mpg (US) ... 19.3 km/L ... 5.2 L/100 km ... 54.6 mpg (Imp)