Red---A quick way to isolate the no-heat problem inside the car would be
to do the following:
Bring the engine temp up to normal.
Be certain when you pull the heater control knob that the water control
valve wire actually moves the lever up the ramp, at least half way.
Feel the water hoses to see if they're as hot as the rest of the water
pipes/hoses. If water is flowing from the water control valve, the
incoming hose should be at least warm.
If water is trying to go to the heater, but the hose out of it is not so
warm, the most likely possibility is rust blockage somewhere in the
system.
Pull the heater return hose from the engine bay side to see if water
flows from here. (Do all the work here, to keep from needlessly staining
the carpets.) Pull the top, or incoming hose off, if necessary, to
check flow into the heater.
Somewhere during this process, the cause of "no heat" should show up.
Backflushing of the heater core and pipes leading to and from it may
prove helpful, if the cause is determined to be "between the hoses."
Sometimes the cause is blockage of the water return pipe. This is the
one behind the intake/exhaust manifolds. Rust can pile up in the corner.
The fix will be obvious if the diagnosis takes you this far.
Dick Taylor
'73
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