I have a Mazda 6 Skyactive 2012 that blows cold air very often even when I have it on maximum temp. It can work well several days but then suddenly it starts to blow only cold air 😢 I have had it at a mechanic and he has checked everything and says it could be a crack in the engine it self because there are boubles in the expansion tank for the coolant . Could it really be this way ? How? It's a 2012 Mazda with 180000km .