24 Hours of LeMons Project Frankenmiata Miata Coolant RerouteProject Frankenmiata

The Ultimate Miata Coolant Reroute

by Dave Coleman

The lameness of Miata cooling systems is well known. They can reasonably handle the 12-13 hp a naturally-aspirated Miata makes, but when asked to deal with both the increased heat load of turbo boost and the reduced airflow caused by the intercooler, the cooling system starts to cry.

Our Frankenmiata makes almost double the stock power output, and can endurance race in 100+ degree weather with the coolant temp staying under 200 degrees. In more civilized weather, it often stays below 180. There's some magic in our cooling system that I'm going to reveal now for the first time. Of course, this is the first time because I've been too lazy to do it before, not because it's some big secret. Still, it sounds more impactful when I use that "first time" line, doesn't it?

24 Hours of LeMons Project Frankenmiata Miata Coolant Reroute

When most people suffer through their first sighting of our car's front end, they're usually so distracted by the chaos of creativity they fail to notice the absence of a radiator. When we first started building this car, LeMons races were like demolition derbys where everyone just happened to be driving the same direction.

Our previous car, the pimptastic Honda CR-XXX, died an untimely death when its bedazzled dollar sign grille emblem punctured the radiator after the 45th time we rear-ended someone. Determined not to repeat this fate with our new car, we hid its radiator deep in the middle of the car. The odd radiator placement is just a small piece of the cooling puzzle. The real magic starts on the inside.

One of the biggest reasons for Miata cooling fragility is a hidden quirk of the engine's front-drive heritage. In the 323, where the engine was transverse mounted, cool water from the radiator entered the water pump, was pushed in through the front of the block, and exited the rear of the cylinder head. This front-to-back cooling flow did a reasonable job of cooling all four cylinders evenly.

When the engine was turned north-south and stuffed in the Miata, the rear-mounted thermostat housing/coolant exit was repurposed to feed just the heater. The thermostat and upper radiator hose were relocated to the front of the head. As a result, most cooling flow goes in through the front and out through the front, leaving water flow in the back of the engine relatively stagnant.

This same design quirk applied to 1.6 and 1.8 Miatas until the 1.8 with variable valve timing in 2000 finally introduced a head gasket that only allowed coolant to pass from the block to the head around the #4 cylinder. This finally forced coolant to flow front to back across all four cylinders, up to the head, and then back to front across all four combustion chambers. 1.8 Miatas have different bore spacing from our 1.6, though, so that head gasket won't solve our problem.

Instead we did the fairly-common Miata coolant re-route, where you return to the old, front-drive coolant flow strategy. Several companies sell kits to make this a reasonably-simple thing to do without re-engineering your entire car. With no money and lots of engineers, we did it ourselves.

24 Hours of LeMons Project Frankenmiata Miata Coolant Reroute

I stole this picture from some guy on MiataTurbo.net, and I'm pretty sure he stole it from someone else, so I have no idea what the original purpose of those arrows was, but here's what the back of a Miata head looks like. The first thing you do with a coolant re-route is remove this heater hose fitting (red arrow) and replace it with the thermostat housing and thermostat.

Unfortunately, that green sensor is the coolant temp sensor for the ECU, and it has to be on the hot side of the thermostat.  Those fancy kits usually include an aluminum spacer, with a tapped hole for this sensor, that goes between the head and the thermostat. We did without such luxuries and instead removed the superfluous hose nipple (green arrow), and tapped the resulting hole for the coolant temp sensor. This is not the kind of thing you want to do with the engine installed in the car, but it was an easy solution for us.

24 Hours of LeMons Project Frankenmiata Miata Coolant Reroute

As you can see here, the temperature sensor is very close to the thermostat.

24 Hours of LeMons Project Frankenmiata Miata Coolant Reroute

So close, in fact, that we had to remove that praying mantis looking doodleframus from the thermostat on the left, leaving us with something like the one on the right.

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OMG Its Weasel
OMG Its Weasellink
Tuesday, June 26, 2012 7:57 PM
Active aero on a 500 dollar car.

This is why we love you Dave.
Wednesday, June 27, 2012 3:27 AM
THANK GOD DAVE! Where have your awesome articles been? I almost gave up and bought a ford festiva after that week long forced V8 article adventure. Great article, thanks for Colemaning up MotoI.Q. again.
Wednesday, June 27, 2012 5:06 AM
Oh boy a Scoobie Lemon? That should be interesting...
Wednesday, June 27, 2012 8:12 AM
you should have made the air exit out of the bottom and made a "blown diffuser" setup haha im sure Adrian newey wont mind
Wednesday, June 27, 2012 8:42 AM
Pure awesome, keep writing articles like this!
OMG Its Weasel
OMG Its Weasellink
Wednesday, June 27, 2012 2:01 PM
This article is the only reference on the internet to the word "doodleframus".

Again, leave it to Dave Coleman to coin a technical automotive term.
Dave Coleman
Dave Colemanlink
Wednesday, June 27, 2012 4:53 PM
I thought you were joking, but I just tried it and there really is only one result. Wow, I feel so special now!
Wednesday, June 27, 2012 7:49 PM
Great article man!!! Your articles always make me laugh ,an. Great stuff there!
Wednesday, June 27, 2012 9:36 PM
The coolant reroute that Mazda did for the Miata is the same thing RWD 4G63 guys are trying to do now. I don't think that modifying the 4G63 head to work like this is worth it. So I have routed my coolant similar to what you're doing and other Miata owners have done with the thermostat housing at the rear of the head.

It almost seems weird that you guys put so much thought into this and still make it look so haphazard. You're just that good.
Thursday, June 28, 2012 1:59 PM
Dave is my idol. I still remember reading the article in SCC where you coined the term Dave's Point. Is that in the automotive textbooks yet? Also, since you're at Mazda now, I'm fully expecting Mazda cars coming out in the near future to be ridiculously awesome, especially the Miata.
Der Bruce
Der Brucelink
Thursday, June 28, 2012 8:37 PM
A BRAT!? Dave, I'm shocked you guys didn't go with a million mile turbo diesel platform to get a mileage(aka less pitting)/torquey combo.
Dave Coleman
Dave Colemanlink
Friday, June 29, 2012 6:17 AM
How do you know we're not putting a turbodiesel in the bed of the BRAT? Anything is possible...
Der Bruce
Der Brucelink
Friday, June 29, 2012 8:27 AM
Haha anything IS possible with you Dave! You're right, I shouldn't assume anything with the motor...
Monday, July 16, 2012 1:44 PM
That's my picture with all the dumb arrows. Behold it.
Thursday, September 19, 2013 6:31 PM
Dave: i was at Thunderhill last weekend helping pit for a team (the A-lone Ranger, if you must know) And when the surprise dyno selected your car to be tested I noticed something odd. The odor coming from the exhaust smelled more like R/C glow fuel than gasoline. Care to elaborate?
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