mazda heater help

[poppa]

We have a 2002 Mazda Millenia , when we're on the freeway heat is great. In town ,every stop light we come to it blows cold air and the gauge rises. It's a 2.5 . Thermostat ?? (I'm hoping that and not water pump) I occasionally smell anti freeze .Looked and didn't see any and no puddles.

[Cooter]

Something is leaking coolant causing an air "pocket" which is why I suspect no heat when idling/low RPM's. I suspect coolant hasn't been serviced/flushed since new?

Also, I've seen water pump "vanes" completely eaten by acidic coolant which will casue a flow issue at low RPM's.

[Indygenerallee]

Check anti-freeze level if it's low it will cause air pockets and overheat then come back down, just had a 05 Jeep Grand Cherokee in and it was low and had a air pocket. Check and  make sure the heater core hoses are hot while running at least it will give you a hint, Could also be the thermostat cheapest repair, Im not sure what the water pump impeller is made of but I always ran into this on the 3.5 Intrepids since they had a plastic impeller on a steel shaft as the engine would heat up the impeller would "free spin" causing a overheat issue and blowing cold,  few different things it could be.