Coolant Expansion Tank

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.

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!

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.

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 return 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. The tank should be filled about half way 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.

4. 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.