The 2015-2020 BMW F8X M3 and M4 rely on auxiliary radiators mounted low in the front corners of the car to keep the S55 in its operating window. Under sustained track use and aggressive street driving, the factory units run out of cooling capacity and heat-soak between runs - and their low position leaves them exposed to road debris and the plastic end tanks prone to cracking under repeated heat cycling. The Mishimoto Performance Auxiliary Radiator replaces the stock unit with a larger, fully reinforced aluminum core engineered to add thermal headroom and survive the conditions that retire the OEM part early.----The core carries 9% more volume and 32% more external tube area than stock, rejecting more heat into the airstream when the engine is working hardest. Strutted tubes reinforce the core against the vibration and impacts that fatigue a low-mounted radiator, while removable stone guard shields the exposed face from debris. Aluminum, TIG-welded end tanks replace the failure-prone factory components, and a robust bracket design fits both the driver and passenger-side locations from a single part.----Direct fit for the 2015-2020 BMW F8X M3 and M4 - installs in the factory auxiliary radiator location with no cutting, fabricating, or adapter work required. Backed by the Mishimoto Lifetime Warranty.

• 32% more external tube area for greater heat rejection - paired with a 9% larger core volume, the expanded core moves more heat into the airstream than the stock auxiliary radiator.
• Built for back-to-back track sessions - the upgraded auxiliary radiator adds the cooling capacity the S55 needs to hold temperatures through sustained high-load driving, where the factory unit heat-soaks and gives up margin.
• Confirmed direct fit for the 2015-2020 BMW F8X M3 and M4 - installs in the factory auxiliary radiator location with no cutting, fabricating, or adapter work required.
• Mounts on either side of the car - a robust bracket design fits both the driver- and passenger-side auxiliary radiator locations, so a single part covers either position.
• No plastic tanks to crack - aluminum, TIG-welded end tanks replace the factory components that fail under repeated heat cycling and high-output use.
• Own it for life - backed by Mishimoto’s Lifetime Warranty, your investment is protected long after install day.
• Removable stone guard shields the core - protects the exposed face from road debris thrown up at the front of the car.
• Strutted tubes resist vibration and impact - internal tube reinforcement strengthens the core against the road vibration and debris strikes that fatigue a low-mounted radiator over time.