MISHIMOTO Ford Focus RS Expansion Tank, 2016-2018

The Mishimoto Expansion Tank adds reliability and refined engine‑bay styling to the 2013–2018 Ford Focus ST and 2016–2018 Ford Focus RS. The factory plastic tank is susceptible to fatigue, discoloration, and long‑term failure due to continuous thermal cycling. Mishimoto replaces the OEM unit with a fully TIG‑welded aluminum tank engineered for durability and consistent performance.

Internal baffles are incorporated to prevent coolant starvation at the overflow ports and to reduce sloshing during high‑speed cornering, braking, and acceleration. A sight tube provides clear visibility of hot and cold coolant levels, simplifying routine maintenance. The tank reuses the factory expansion‑tank cap and features an overflow nipple on the fill neck to support the addition of an auxiliary coolant reservoir for NHRA compliance.

The stock tank is a notable engine‑bay eyesore, while the Mishimoto replacement is available in black, wrinkle red, or Wrinkle Nitrous Blue to complement vehicle styling. Installation can be completed in under one hour, and the tank is engineered for perfect fitment across both Focus ST and Focus RS platforms. As with all Mishimoto Focus RS/ST components, the expansion tank is backed by the Mishimoto Lifetime Warranty.