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.