An obstructed heater hose inlet quick connect fitting can cause the engine to run hot. The heater core inlet fitting is the heater fitting that is closest to the centerline of the car. The thermostat senses the temperature of the coolant from the return side of the heater core circuit. The connector also has the heater coolant flow restrictor. The hole is about 5/16" and can become clogged. The connector in the picture is about 50% obstructed. A common source of debris is the inner seal of the thermostat. When the thermostat gets very old the inner seal disintegrates and the fragments can accumulate in the heater flow restrictor. In addition to reducing heater performance the thermostat may require more time to sense the coolant temperature and open later than it should.

A partially obstructed connector can be cleaned by back flushing the heater core. Remove the thermostat before back flushing.

It is extremely difficult to disconnect the heater hose from the fitting. I have learned to not waste time trying to remove it. I chisel off the two metal bars to release the hose. Then a new fitting is installed.

The connector sometimes corrodes internally. During removal of the fitting, it can break off on the threaded end. In an effort to avoid breaking it off, remove the thermostat and apply heat to the inside of the thermostat housing with a torch.

The fitting below is from a car with only 3,700 miles. The heater coolant could not flow because it was completely obstructed. The corrosion was caused by extremely old coolant.

 

 

 

 

 

 

 

 

 

 

 

 

 

Completely obstructed fitting.                                          New fitting.

Dorman supplies the fitting. PN 800-401