You need to by no means blend two types of coolants. If they are of various formulations, doing this may lead to significant, irreversible damage to the engine and cooling process. Commonly, you should have your 2012 BMW 335i coolant flush concluded each 30,000 miles or each individual two years. https://automotive13876.blogocial.com/types-of-coolant-for-bmw-335i-things-to-know-before-you-buy-63395434