My van has been to the shop several times in the last six weeks for the
same problem. The heater blows cold air when idleing. The engine is hot,
Heater hoses are hot also. Several thermostats later I decided to work on
it myself. After rerouting the hoses and checking the valve I disconnected
the hoses and ran two clear hoses into a bucket of coolant. The coolant
only flows when the engine is running at a high rpm. Is the water pump
supposed to circulate at an idle???