Project MR2 Turbo: A Trick Mishimoto Radiator for Our SW20 MR2

Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Oct 14, 2020

Cooling your turbocharged sports car is a priority. For our 1991 Toyota MR2 Turbo, Mishimoto had a drop-in solution.

As we progress with our SW20 MR2 Turbo project, you might notice a theme of coolness. Yes, the car is very cool, thank you for noticing, but the kind of coolness we’re actually talking about is keeping the power-producing portions properly prepped to promote peak performance.

Turbocharged engines produce lots of heat. The mere act of compressing air tends to increase the temperature; add in turbine wheels spinning at tens of thousands of rpm, and you have a recipe for thermal energy, and heat is the enemy of both horsepower and engine longevity. So, before we take many steps to increase the power, we’ll do our best to ensure that we’re not losing any power–or putting undue stresses on our powerplant–by taking some steps to manage heat.

Even though the second-gen MR2 wasn’t built in the numbers of contemporary sporty cars like CRXs and RX-7s, there’s a dedicated enthusiast base, and that base is rewarded with some high-quality, drop-in options for upgrades.

For cooling, Mishimoto has multiple drop-in options for the SW20 chassis, including a two-row, upgraded-performance radiator, and the X-Line high-performance radiator (about $360) that features three rows of cooling passages and occupies every available millimeter of space allotted to it in the nose of the car for optimal cooling performance.

When it comes to radiators, increasing efficiency is fairly simple in theory: Expose as much coolant as possible to as much air as possible and allow it to transfer its heat to the ambient airstream before it returns to the engine. But the reality is that heat exchanger needs to fit within the physical confines of the car itself, so design and packaging becomes crucial to performance. Mishimoto employs such strategies as thinner-wall tubing to promote heat transfer plus a higher density of cooling fins to provide additional heat sink area for the heat from the cooling tubes to transfer to via conduction.

Cooling a mid-engine car is even trickier than a traditional front-engine car: The coolant has to make the long trip from the engine to the front of the car where the radiator is located, then back to the engine. That additional piping does provide additional radiant heat transfer, but the engine being out of the line of direct airflow places even more demand on the radiant cooling components.

Mishimoto’s win with the X-Line is not just in excellent construction and lots of capacity, but the way that it maximizes the available space in the nose of the car to pack as much thermal transfer technology possible into the available space. If your car has ever had any front end damage, you’ll know how well it was fixed when you install an X-Line radiator, because any errant sheet metal or support structure might interfere with the precision fit of the upgraded unit.

Here’s our step-by-step of our install experience.

1. We started off with the car on our QuickJack, which seems tailor-made for a job like this. If you’re doing this job alone, you’ll be making several trips from under the car to over it, and having the ability to quickly change the height was a plus that wouldn’t be afforded with fixed jack stands. Start your job by removing the trim panel from under the front end of the car. It’s held on with several push fasteners and several 10mm screws.

2. You’ll have to remove some trim from the frunk, too. That black panel right behind the Toyota badge is held in by several plastic push fasteners. Pop those loose and remove the panel to reveal…

3. …the top of the radiator. Remove the two large black radiator hold-downs (you’ll need a 12mm socket), undo the two electrical connections to the fans, and remove the two bolts holding the top of the fans to the radiator using a 10mm socket.

4. Now head below and you’ll see… OH MY GOD HAVE THOSE FANS BEEN AT THE BOTTOM OF THE OCEAN!? Nope, just New Jersey, where our car originally came from. They’re gnarly, though, as are those brackets securing the a/c condenser. Luckily those condenser brackets can stay in place (although we’ll take another evening to properly deal with them before that rot spreads to the frame of the car), but the four bolts holding the bottom of the fans need to come out with your 10mm wrench. Don’t get any rust in your mouth. Once freed, the fans remove easily from under the car.

5. Now you should have a nice view of the back of the stock radiator from underneath. You can reach up and remove this electrical connection on the temperature sensor. You’ll also need to remove the two large hoses connecting the radiator to the cooling system. Undo the clamps (our car had screw clamps, but spring clamps were the OEM solution), and gently push the hoses back off the inlet and outlet. You don’t want to damage these hoses if you aren’t planning to replace them, because replacing them is a grade-A pain in the butt.

6. Now we can drain the radiator, or the entire cooling system if you’re so inclined. And, really, if you’re doing the work, go ahead and drain the entire cooling system. The radiator has a drain petcock in the bottom of the passenger side, and the entire cooling system can be drained through the drain plugs mounted on the coolant hard lines at the lowest point of the cooling system, which is almost exactly midship on the car.

7. If you have a naturally aspirated MR2, your radiator can now be removed from the top. If you have a Turbo–which came equipped with a slightly larger radiator from the factory–you’ll need to lift it up slightly to disengage it from the sockets on the bottom, then tilt the bottom of the radiator toward the back of the car and lower it out the bottom.

Our stock radiator featured the ghostly image of a long-dead rat embedded in its fins. We do not think this was a factory option.

8. The bottom of the radiator is held in place with some rubber-isolated bushings that capture pegs on the bottom of the radiator. Yours are probably gross. Take them out and clean them up with a wire brush and give them a coat of paint. It will make it easier to get the new radiator in, as the pegs on the bottom of the Mishimoto are designed around the specs of the original bushings, which did not feature crusty, rusty flakes.

9. The Mishimoto X-Line radiator is a sexy thicc boi: almost twice as thick as the original, featuring an additional row of cooling passages, and 30% more total cooling capacity. Despite the increased size, somehow it still goes in the same hole.

10. Gently remove the temperature sensor from your original radiator (flare nut wrenches work great for this), clean up the threads with a wire brush, apply some Teflon tape, and install it in the new radiator.

11. Now it’s time to raise it into place for a test fit. Here’s where you find out if your car has ever been in a wreck. Does it fit properly? Great. You just saved a few bucks on a Carfax.

12. These upper hoses are a real pain in the butt to get on, especially now that you’re dealing with a thicker radiator, which give less room to maneuver. Here’s the trick: Once the radiator is completely in place, it’s just not going to happen. So slide on the hoses with the radiator still hanging out the bottom of the car a bit. This give you a better angle, and more room to work. Apply a little liquid soap to the inlet and outlet to help things slide into place easier.

13. Ugh. These fans are awful. We should probably replace them. We wonder if Mishimoto also has fans for this car? Hmm (That’s foreshadowing, kids). But for now, they need to go back in. If your fans aren’t gross and you plan on reusing them, you may need to clearance the little notches right above the brackets that hold them to the lower part of the radiator. We had to grind back around 3/8 of an inch of shroud material to clear the bosses on the radiator. We’re not going to blame Mishimoto for this, though, because look at those fans. Whatever happened here is clearly their fault.

14. Now we can start putting things back together topside. Reconnect the fan plugs, fasten the fans to the top of the radiator, and install the hold-down brackets.

15. Now it’s time to begin the complex and often frustrating process of bleeding an MR2 cooling system. We’ll be refilling our system with Mishimoto’s Liquid Chill synthetic coolant, which they claim to have advanced anti-freeze, anti-boil and anti-corrosion qualities. Coolant boiling in an MR2 is a disaster waiting to happen, as any air in the cooling system can cause temperatures to spike immediately, possibly leading to head gasket failure or worse.

16. Start the bleeding process by opening the bleed hole on the top of your new radiator.

17. MR2s also should also have a bleed tube in the frunk that connects to a bleed port attached to the heating system. Turn on the heat all the way, attach the bleed tube, open the bleeder screw (it’s the white knob), and this now becomes the high-point of the system for the air to bleed.

18. Fill the cooling system at the pressure cap in the engine compartment until coolant spews out the radiator bleed hole. That’s how you know the radiator is pretty much full. Now you can pop the cap back on the radiator bleed. We used the full-strength Mishimoto Liquid Chill ($64.95/gal) mixed 50/50 with distilled water. Mishimoto also sells premixed 50/50 Liquid Chill ($40.95/gal) that can be poured in directly from the jug.

19. Top off the system at the fill port, leave the heater bleed open, then start the engine with the cap off. Watch for bubbles and keep an eye on the temperature gauge. When the thermostat opens…

20. …the system will drink up the additional coolant to fill the rest of the system. Continue adding coolant to keep the system full at the fill port. If you allow it to suck air in at this point, it just prolongs the process.

Once you’re topped off and stable at the fill port after the thermostat opens, close the heater bleed screw and continue to let the car run with the fill port uncapped. Keep an eye on the fill port and keep the system full.

After 15-20 minutes of running and filling, you can close the system and go for a SHORT drive. Keep a close eye on the temp gauge. After a few minutes of driving, park the car, let it cool off a bit, then remove the fill cap and top it off. Check it before each of your drives for the next few days, and keep a jug of premixed coolant ready to top it off. Remember to NEVER open the cooling system with the car at operating temperature.

21. Head to the track! With your additional cooling, your MR2–Turbo of otherwise–should be much better suited for the rigors of track or autocross use. On our first track outing we had zero cooling issues, and strong performance on a 90-degree Florida day from our increased-efficiency Mishimoto X-Line radiator.

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View comments on the GRM forums
stylngle2003 GRM+ Memberand Reader
10/15/20 11:50 a.m.

not going to lie, the rat in the radiator is pretty gruesome.  slow roasted to death

JG Pasterjak
JG Pasterjak Production/Art Director
10/15/20 12:50 p.m.
stylngle2003 said:

not going to lie, the rat in the radiator is pretty gruesome.  slow roasted to death

I didn't actually even notice it until I was looking at the photos. Up close you couldn't really get the full effect.

300zxfreak Reader
10/25/20 12:44 p.m.

I did the same radiator swap in my Z32 TT, along with the secret weapon, a Million thermostat, apparently only available directly from Japan these days. Along with an oversized oil cooler install, the normal operating temps dropped by a good 10-15 degrees. I still may look into getting a stock hood on Fleabay and install vents for driving on bright, sunshiney days.

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