Add some reliability and engine bay styling to your Focus RS/ST with the Mishimoto RS/ST expansion tank. This tank features internal baffles to prevent coolant starvation from overflow ports on the engine. Also, during high speed cornering, braking, and acceleration, the internal baffles reduce coolant sloshing. The engineers at Mishimoto have included a sight tube to allow for proper observation of hot and cold coolant levels, making engine maintenance much easier. Eventually, you'll have to consider the health of your plastic expansion tank. Plastic is prone to failure after years of constant temperature variations. The Mishimoto tank is constructed from durable, TIG-Welded aluminum for optimal durability and longevity. It reuses the stock expansion tank cap and includes an overflow nipple on the fill neck for adding an additional coolant tank so your Focus RS stays NHRA legal. All areas of concern are covered with this upgrade. It's worth noting the Focus's stock tank is an engine bay eye sore, whereas the Mishimoto tank comes in three different variants to help with aesthetic customization: black, wrinkle red, or Wrinkle Nitrous Blue. Each of these options works with both the 2013-2018 Focus ST and the new 2016-2018 Focus RS. For convenience, you can install your new coolant tank upgrade in under one hour as it was engineered with perfect fitment in mind. Like all our Focus RS parts, this expansion tank also includes the Mishimoto Lifetime Warranty.