Racing Line's replacement Billet Coolant Expansion Cap for MQB & A5-platform models is a full replacement for the original plastic cap. Keeping that coolant expansion tank sealed is a critical part of your car's cooling system. Racing Line's replacement cap will ensure that proper pressure is maintained, and never exceeded, especially on high-performance engines. Doesn't your pride and joy deserve better than cheap plastic parts in the engine bay? The Racing Line Coolant Expansion Tank Cap will keep your coolant expansion tank at its perfect pressure to be sure that your high-performance engine’s coolant system is performing exactly as it should. Of course, the cap's a critical part of your car's cooling system to ensure that correct pressure is maintained, and never exceeded. Older, worn stock coolant caps lose the ability to hold correct pressure to keep the coolant at maximum efficiency. Don’t confuse this Racing Line full replacement cap with other cheap covers - which simply stick on over the plastic cap. We think your car deserves better than that. This is an engineered, billet replacement coolant cap to replace the cheap plastic one, with sophisticated internal springing and bleed off system. As you’d expect from Racing Line, it’s meticulously machined with the latest CNC 5-axis technology. Each cap starts life as a solid billet of 6061 aerospace-grade aluminum. It’s then hand-polished, then gloss-anodized Midnight Black to stay beautiful year after year.