Originally Posted by scoobyJim2

Water pump does pump water around you're right but if your talking about changing/refilling coolant system then you have to turn heaters to fully on and this gets the water around the heater matrix, which is closed untill you turn on heaters,as its the heated water that allows heaters to come out warm (engine & heaters use same water)

Originally Posted by Don Clark

Jim, did you read the rest of this thread before posting??

The whole point is that, the heater matrix on a Subaru (and many other cars now) is a full flow matrix and does not have any valves that close it off from the rest of the system.

All the heater switches do are to operate flaps that mix cold and hot air to the required temp.

As previously said the necessity to put the heater switch to hot is a total misconception on modern cars.

Originally Posted by matthewn

changed coolant and my heaters blows warmish air, got no leaks,have i got a air lock? how do i get rid? pump bottom hose when idling with header cap off with heating on full blast and full speed ? temp fine and no hg failure tested all that, and i back fed via tub hose!and checked thermostat. anyone?

Originally Posted by alcazar

But, as above, I don't think there is actually a valve that diverts water away from the heater matrix, just a flap that diverts AIR over it, for warm, or not, for cold?