Heater core flush

The flush operation is pretty simple (compared to attempting to remove the heater control unit in the dash which was before I realized that the manual unit my car has doesn't have a pc board to check for cracked solder joints like the pushbutton models do. I'll do a separate post on how to disassemble the dash to remove the control unit for anyone that needs to do that).

So, the issue is there is no heat in the car. The fan works, and all the slider controls work as well. I check the heat selector in particular that actuates a valve on the firewall, allowing more or less radiator fluid through the heater core depending on the heat selection. The valve operated easily as I changed the heat selection.

I warmed the car up and checked both the inlet and outlet hoses (they are just above the valve in the picture, going through the firewall) and sure enough, the inlet hose (going from the valve to the firewall, far side) was good and hot but the outlet hose (pictured in the middle between the valve and the inlet hose) was lukewarm at best. I attempted to remove the hoses at the firewall and had two issues: the hose clamps are royal knuckle busters to move if you don't have hose clamp pliers. I did it with channel locks and a needle nose but it was not fun. The second issue was I could not break the hose loose from the inlet and outlet pipes. They are copper pipes and I was worried I would break them if I wrestled the hose any harder, so I removed the hoses at the other ends. Both hose ends are below radiator height so I had to plug the outlet pipe on the water manifold and inlet pipe on the block to keep from losing too much fluid.

The flushing was pretty simple. I placed a harden hose sprayer in the end of the inlet hose to start, and slowly increased pressure until I had good flow on the other end. Brown, muddy fluid came out which is a good indication it was blocked and not getting good flow. I switched back and forth between inlet and outlet hoses until the water ran clear in both directions. I reconnected the hoses, fired the engine back up and let it warm up...and booyah! Hot air is now blowing from the heater.