Hi I’ve got an issue with with my 2007 mazda5 ts2 firstly I have a over heating problem, the problem only occurs when doing 50 plus but can sit in idle for an hour and it stays steady, it’s also using coolant and I can’t see any leaks and very concerned it’s the head gasket, also the heater only works when driving and not while idling. My other query is where the hell is the thermostat I can’t seem to see it anywhere!! Any help would be greatly appreciate.
im in the UK if that makes any difference also it’s a 2007 ts2 diesel not the facelift one. And another thing sometimes coolant is boiling/bubbling out of the expansion tank

 

I would book it in with a reputable garage for a complete diagnosis. I could start asking you a whole heap of technical questions.