Compatible: (2.0L/2.5L)

2008 – 2021 Subaru WRX

2008 – 2014 Subaru WRX STI

After a few hot and cold cycles, Mishimoto recommends checking the dipstick on the expansion tank to confirm proper coolant level.

Get that plastic blob of an overflow tank out of your engine bay. Stock plastic tanks are prone to failure due to repeated hot and cold cycles, and they create a horrible eyesore as they lurk in your engine bay. Mishimotos 2008-2021 STI / WRX coolant overflow tank is constructed from durable, TIG-welded aluminum for optimal durability and longevity. Included with this STI / WRX coolant overflow tank is a CNC-machined dipstick to allow for easy checking of coolant levels. With the choice of two finishes, polished and anodized black, this tank will have no problem matching the style of your engine bay. This STI / WRX coolant overflow tank fits perfectly with the stock or Mishimoto STI / WRX radiators. As with all Mishimoto STI and WRX parts, this overflow tank includes the Mishimoto Lifetime Warranty.

• Direct fit for the 2008-2021 Subaru WRX & STI
• Installs in under 30 minutes
• All-aluminum, fully welded construction for maximum durability during repeated cold and hot transitions
• Dipstick allows for proper cold coolant levels
• Available in polished or anodized black
• Includes black Mishimoto fill cap
• Mishimoto Lifetime Warranty

VEHICLE SPECS

PRODUCT SPECS

PURCHASE INCLUDES

(1) Aluminum Expansion Tank
(1) CNC-Machined Dipstick
(1) Mishimoto Oil Fill Cap
Mishimoto Lifetime Warranty

2008+ SUBARU WRX/STI ALUMINUM COOLANT OVERFLOW TANK R&D!

If you havent noticed, the folks here at Mishimoto are not fans of plastic use for cooling system components. A large number of our products provide a more durable material, aluminum, to replace the failure-prone plastic parts, and now we are focusing on another line of products, our aluminum coolant expansion tanks. We offer two different options for the WRX/STI and one for the new Mustang EcoBoost. This article is focused around our newest addition, an aluminum overflow tank for the 2008+ WRX and STI.

Product Design

We wont be making any significant changes to the design of this tank compared to the stock unit, except for the construction material. Enlarging the tanks capacity will have no impact on fluid temperatures or cooling efficiency, so this will not be necessary.

We snagged a stock overflow tank and started gathering our dimensional data.

Stock WRX overflow tank on CMM table for new WRX parts development

For accurate modeling, we are using our CMM (coordinate measuring machine) and Romer arm. These devices allow us to stabilize the tank in place to collect critical dimensions for the tank shape and mounting points.

Stock WRX overflow tank on CMM table for new WRX parts development

From this model, we were able to design our prototype tank. We also happen to have a 2015 WRX of our own, making slight tweaks for fitment as simple as a walk into the garage. Our engineers came up with some 3D renderings of the prototype design. Check it out!!

Rendering of Mishimoto WRX coolant overflow tankRendering of Mishimoto WRX coolant overflow tank

The fill neck of our tank is designed to reuse the stock cap. This piece was easily removed from the stock tank and installed on our prototype. The front face of our tank features a sight tube for checking fluid level.

Here is a look at the top of the tank!

Rendering of Mishimoto WRX overflow tank

Heres a look at the lower mounting peg, which secures the base of the tank within the fan shroud.

Rendering of Mishimoto WRX overflow tank

You will also notice our M logo stamped into the aluminum tank.

Prototype Installation

After finishing the models, we ensured that our dimensional data was correct and then worked up a prototype for test fitting. Check out a few shots of our first prototype installed.

New Mishimoto WRX parts installedNew Mishimoto WRX parts installed

As you can see, the stock overflow cap fits perfectly on our aluminum tank.

We designed our tank to function with a rubber grommet to keep the overflow hose in place within the tank. Additionally, we are including a silicone overflow hose that runs from the radiator fill neck to the tank. Check out the complete installation!

Mishimoto WRX coolant overflow tank prototype installed

With the successful test fit and all components mating up perfectly, we are ready to start manufacturing our first batch of tanks.

2008+ SUBARU WRX/STI ALUMINUM COOLANT OVERFLOW TANK R&D UPDATE!

We last left you with some details of our initial design and a hint of an upcoming pre-sale for this overflow tank. Unfortunately, since that initial test fit we hit a few snags in the design process. Our goal with this product is to provide compatible fitment with all our other 2008+ WRX and STi components. This required numerous stages of test fitting, one of which revealed an issue. With our larger 3-row X-Line aluminum radiator installed, our sight tube on this expansion tank design ended up too close to the belt drive system on our Subaru.

We decided a revision was necessary. Although the two components were not physically touching, the clearances were just too tight for our comfort. Luckily, our team had an alternate means of measuring fluid within the tank. This comes in the form of a dipstick!

Check out a few 3D models of our new STi / WRX coolant overflow tank design.

Mishimotos STi / WRX coolant overflow tank 3D modelMishimotos STi / WRX overflow tank 3D model

For the most part our STi / WRX overflow tank design has remained the same. Mounting points and basic shape are identical to the previous design, but instead of the sight tube, we are now using a dipstick. This component is not new to our line of aluminum tanks; we use a similar piece on our E36 BMW tank and it functions perfectly.

The stamped logo shown on our previous models and functional prototype remains. This is a nice subtle method for placing some branding on our new STi / WRX parts.

Since the dipstick is the primary reason for the design change, lets take a closer look at this piece.

Mishimotos ST