1993 Taurus GL heating
Just to share :
As winter came on us, i have found that the internal heating was not working. air was coming out cold.
so i checked the two hoses inside the engine bay - inlet was very hot, the outlet (passenger side) was less than warm.
i thought maybe the heat exchanger is clogged - so i removed the two hoses, and plugged a piece of hose to the inlet and put its other side outside the engine bay. i then connected a hose which i use to water the plants to the outlet of the heat exchanger and open the faucet slightly so not to stress the heat exchanger - i then saw all the dirt come out of the inlet - first some coolant came out but then color changed to brownish rust. eventually the water came out clean. i then closed and re-open the inllet hose by bending it so to give some high pressure hits to the system which helped bring out some more dirt. then i switched between the inlet and outlet hoses and so gave several hits to the system in the normal direction with the water faucet opened to its max. it took out some more dirt.
i then connected everything back, and let the engine heat up - everything now heats like should be...