The heater wasn't working so I looked at all the possibilities (felt the heater hoses under-hood, checked the flap doors, felt the hoses behind the heater core and only the inlet was hot.) Baffled, I figured I would start with a new heater bi-pass valve and do a quick flush.

Disconnect here for the direct inlet flush with the garden hose

This is the heater bipass valve I started with new

This comes from the return line of the core, remove hose here and the front hose goes here temporarily, you can new see the new bipass valve on the left (front of truck). If you don't use the temporary front hose here the coolant will flow directly onto your cops and boots.

This front hose connects to the return outlet temporarily and drape it around the oil fill tube so you don't get water on the cops. You need to put it back last because the steel pipe it connects to is where you need to bleed the air at the manifold. The garden hose goes in the end of this to back-flush the core.

This is the front hose again, it goes on the return fitting in the back temporarily and it used for the return back-flush with the garden water hose


I don't know what I did (because the old bipass valve seemed to be OK and the water wasn't very dirty) but the heater works great now so I can't complain.