The overflow expansion tanks are exposed to incredible heat and pressures, causing the plastic hose fittings and joins to crack without warning. Running low on coolant can cause your BMW to overheat, leading to expensive engine problems. With the high failure rate of the these expansion tanks, we recognise that the market has been flooded with notoriously cheap aftermarket replacements. This is why we choose to offer expansion tanks from cooling system supplier to BMW, Behr Hella.