Coolant Expansion Tank

Wilhelm Raceworks coolant expansion tank for SW20 MR2

Replace the coolant overflow tank on the MR2 with a modern pressurized expansion tank.  This eliminates most of the hassle associated with bleeding the air bubbles out of the MR2's cooling system, and reduces the risk of a sudden drop in coolant pressure causing local boiling within the motor.  See my blog on the subject for more details.  For 2GR and other engine swaps, this also allows you to skip modification of the coolant neck to add the filler cap.

Wilhelm Raceworks coolant expansion tank for SW20 MR2 Wilhelm Raceworks coolant expansion tank for SW20 MR2 Wilhelm Raceworks coolant expansion tank for SW20 MR2

Expansion tank mounts to the left side strut tower using existing threaded holes.  Includes tank and mounting hardware only.  You will need to supply a length of 5/8 heater hose for connection to the heater return line, and a length of 1/4" hose to run from the radiator bleeder back to the expansion tank.

These are semi made-to-order.  I will attempt to keep a couple in stock, but it will depend on demand. 
Made in the USA!

SKU Coolant Expansion Tank
1 In Stock
Mounting Location:

Coolant expansion tank installed. Coolant expansion tank installed.
Wilhelm Raceworks expansion tank installed Wilhelm Raceworks expansion tank installed


Optional Fuse Box mounting location, stock fuse box must be relocated.

Wilhelm Raceworks coolant expansion tank - fusebox location Wilhelm Raceworks coolant expansion tank - fusebox location

Installation Notes:

1. As noted above and in my blog, the large bottom port on the tank connects to the heater return line, or other port on the water pump inlet side of the motor.  You can simply T it into the heater return line.  Make sure you use the heater return, not the feed. (On the 2GR-FE this is the lower port, on the metal pipe that runs through the V.  The port on the water neck under the throttle body is the feed to the heater.)

2. The small port on the tank must be at minimum connected to the radiator bleed port in the front of the car.  Optionally you can also T the heater core bleed into the radiator bleed line, but creating a reliable connection to the heater bleed port is more difficult.  If you choose not to connect to the heater core you will still need to bleed that manually, but making the radiator self bleeding will still be very helpful.

3. If installed with the 2GR, you may wish to add a line from the 2GR's bleed port (between the cylinder heads, to the right of the intake manifold).  Or you can manually bleed this point on initial fill.  On other motors (such as the 3S/5S), it may be necessary to add a bleed port at the motors high point (on the 3S, that would be the stock fill point), and a bleed line from there to the tank if you wish to make this point self bleeding as well.

4. The tank should be filled about half full when cold.  You need about 3.5-4 inches (89-102 mm) of air space in the tank to allow for coolant expansion.  If you over fill it, it will push coolant out of the radiator cap when hot.  On initial fill, run the engine for a few minutes with the radiator cap off and monitor the level in the tank.  The system should self bleed (assuming bleeder lines from the radiator and heater core), but only with the engine running.  You should be able to see a steady stream of coolant from the bleeder line (looking through the radiator cap with a flash light).  You may need to rev the engine a little to see this, at warm idle there may not be enough flow to purge the bleed lines.

5. The tank will take the same type of radiator cap as the stock MR2.  However, I recommend a 20psi cap for most applications (the stock MR2 cap is 13psi).  Stant part numbers for higher pressure caps can be found below.

Stant Part # Pressure (psi)
10267 20
10265 18
10233 16
10227 13



  1. Thursday, 21 July 2022 08:17
    Hey Alex, Would you consider making one with -AN fittings if requested?
    1. Thursday, 21 July 2022 08:37
      I certainly can.  They are basically made to order, so customization like that aren't hard to do.
  2. Tuesday, 23 August 2022 14:49
    Would you consider making it have a longer neck so it could replace the stock overflow tank but not require the fuse box to be removed
    1. Wednesday, 24 August 2022 09:28
      There is no need to move the fuse box, just use the normal mounting point on the front of the strut tower.  The fuse box location version is just for people who have already relocated the fuse box.  It does need to be the system high point, so putting it down low with a long neck like the stock overflow wouldn't work.
  3. Sunday, 13 November 2022 18:22

    This is an overall good product and works well. One improvement I would suggest is to have some sort of level indicator on the side of the tank for convenience.

    1. Sunday, 13 November 2022 19:08

      Thanks.  I have thought about adding a level indicator, but the only easy and cost effective way I have found is with tube fittings and clear tube, and I just don't like how those look.

  4. Monday, 13 February 2023 02:40

    How much for this and do i need bleed ports tell me also will you paint it for me and how much is a rad cap

    1. Monday, 13 February 2023 08:50

      Check my blog for some pictures of how I setup the bleed lines.  Depending on the motor, you may also need a bleed line from a high point on the motor.  I don't carry the caps, and I would prefer to leave paint / powder coat or other finishing beyond the satin brush that I usually do to the end user.

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