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Heater has mysteriously stopped working.

2K views 8 replies 7 participants last post by  PrimeMover 
#1 ·
I have a 1965 Plymouth 273 V8 with automatic transmission., and the heater has mysteriously stopped working.

About a month ago the heater core started leaking inside the car. I removed it for cleaning and discovered it had a special shut off valve built in the core that was leaking. It was impossible to find another one, so I cut that off and installed a manual shut off valve in the heater hose coming from the water pump. I had the heater core professionally cleaned out, reinstalled the whole thing tback in the car and it worked perfect until now, (about a month later)

I am geting only cold air, (after the engine reaches operating temperature) so I thought the heater core must be plugged up. I disconected both hoses to the heater core, hooked up a garden hose and I am getting great flow from either hose I flush water thru.

The thermostat works because the engine reaches operating temperature in a few minutes, the water pump works good because the engine does not over heat, I get good water flow thru the core from the above test, I get good air flow from the fan across the heater core, but all I get is cold air. Anyone have any ideas.
 
#2 ·
With the engine warmed up, feel the 2 heater hoses. Are they both hot? If they are not, water is not flowing through there. Check that manual valve that you put in.

If both hoses are hot, you have good flow through the heater. Is there a door between the blower fan and the heater core that could be closed?
 
#3 ·
Check the heater core hoses like Poncho said. If they're both hot, check the blend door in the heater case (just follow the cable from the "HOT/COLD" selector lever to whatever arm it actuates and make sure it's attached/operating).
 
#4 ·
Make sure your heater valve is open when you fill your cooling system to allow all the air to be pushed out. Like BstMech and poncho suggested , feel your heater hoses - a cool hose may indicate an air lock in the heater matrix .
 
#5 ·
Still no heat - A real head scratcher???

I tried everything that was suggested and still no heat. The two hoses were both hot. The vent to heater core is open and I get good air flow across the heater core. The manual valve I installed is open.

Am I assuming correctly that the water is supposed to flow from the water pump, thru the core, then thru the hose back to the intake manifold? If not how does it flow?

I tried disconnecting the hose going to the intake manifold thinking I hsould get the return water from the heater core, and did not get any water at all when I started the car and ran it a few minutes.

Is it possible the water pump is pumping to full capacity. How would I check this. Thanks for all the help so far.
 
#8 ·
Just because the engine temp is getting warm in a few minutes like it supposed to doesn't necessarily mean that it isn't the thermosat. I may be stuck partially closed allowing the engine temp to warm up but prohibit the correct water flow. Most thermostats are cheaply produced parts that sadly to say you have about a 50/50 chance of getting one that doesn't go bad quickly. I would say replace the thermostat and try it again.
Later,
WEIMER
 
#9 ·
I had the same thing happen to me a while back, right after I put on a new water pump. Both my hoses were hot but the core stayed cold. I pulled the flow valve and found a peice of gasket material had laid itself flat up against the opening in the valve. It's amazing how small the opening is in some of those control valves. I guess the engineers figured the heater core didn't need full flow. They were right - once I got it cleared, the heater ran me out of the car.
 
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