for a while now, i've had issues with my heating, eventually a garage diagnosed the head gasket had gone. I've had this replaced, all was well. Then a few weeks later, I wasn't getting any hot air out of the blowers. took it back to garage, found it was air locks, fixed & had hot air again. few weeks later, same thing again, air locks, garage fixed & hot air again. Inbetween all this, we were checking coolant level daily and then weekly till it settled.
It's been ok for a few months and now the cold weather has kicked in, suddenly no hot air again. We bled the system by undoing the 2 screws we could see, lots of air released. once all gone I took the car for a drive, after about 10mins, I finally started getting hot air, but when i got to a junction, the air would go cool, as i pulled away and got up to speed, the air would go hot again?? When we got back home, left the engine running and eventually it was just cold air coming out. I undid bleed valves, lots of air in system again and didnt tighten untill all air had gone. sat back in car, still blowing cold air, despite engine being at temperture.
Next morning, i removed air from system via bleed valves, then removed coolant filler cap. started the engine and waited for it to warm up, when engine got to temp, i could see lots of bubbling in the filler tube till eventually just water was coming out. I took car for longer run, and despite been up at temperture before setting off, it was still a good 10mins till hot air started blowing out, but as above, when got to junctions and eventually end of journey, back to cool air? I undid the bleed valves and again, lots of steam being released for a good minute until coolant started coming out. The final notes to add is that one side of radiator is always hot, as I bleed air out of the system, you can feel the other side of radiator warming up? The cars temp always reaches midway, and doesn't appear to overheat. Not sure if it helps, but the header tank is always above the max level...whether this changes when driving..who knows? No coolant leaks either?
Does anyone have any ideas what might be the cause of this. Sorry it's a long explanation but want to get all the facts out to help diagnose this. when the garage replaced head gasket, they apparently tested the water pump and said all was well. Could it be the heater matrix, or is it simply still an air lock? Something else is a dodgy thermostat??
thanks in advance
stressed mini one owner