I noticed the other day that heat would come out of the car only sporadically. The water temperature is hot going into the firewall but cool coming out. I guess the internal valve is defective. On a 73 Duster, it appears that the heat controller is manual and operates by cable so the cable must be good. Is there also a vacuum component? There are 2 vacuum lines going into the dash area and I have thus far only been able to scrounge one check valve. I am thinking that perhaps it is a vacuum valve that opens and closes based on speed. Thanks.

Mike

I think the temperature blend door is cable actuated, but I'm not 100%. Both heater hoses should feel hot if there is good circulation through the core. I don't think these cars use a heater control valve to shut off circulation, so my guess is the core is clogged.

I second the clogged core

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Hey, don't any of you guys go into the pastoring business. Every time I come here for an answer, I hope you have a better one (easier & cheaper) than I do and you always give me my worst fears. ..Just kidding, I did suspect that but hoped it could be something simpler. Everyone here has always been very helpful and given me great help. I seem to have covered every problem possible with this car but I guess it should be expected with a car the previous owner(s) totally neglected and abused. I noticed my manual says I have to pretty much dismantle the entire car to replace the core. Is it possible to flush the core from the reverse direction of the normal flow? As always, thanks.

Mike

to remove the heater core in my 73 dart i just had to take the front of the heater box off. good luck getting those clips back on after youve taken them off. also make sure you get the ones on the top side of the heater box. inside your vent door to the top is a rod that hooks up inside somwhere that has a nut at the bottom that is attached to a bracket on the front of the heater box. i replaced my heater core and my heater still doesnt blow too warm. its the price you pay to roll around in a car as cool as a dart.

I'd try flushing both ways. Since the system is hosed anyway (pardon the pun), you probably won't hurt anything, and might solve the problem.
I did this on a '75 Vega once that had never put out any heat for me. We're talking frost on the inside of the windshield during a 4-hour winter drive. Regular flushing did nothing. Decided to force water the other way. BINGO! Mud came out, then nasty water, but in the end, it worked beautifully.
Crud in the heater core isn't doing your car any good, and may be eating away at the core. A sudden leak there can be a traumatic experience. I've had that, too!

If its clogged this bad, I would disconnect both hoses and when you flush, let it run out instead of back into the engine/radiator. You don't want to get that gunk where it don't belong....

Prestone sells a kit of plastic fittings you can hook up to a garden hose, and the other end to the rubber hose leading to the core. A local parts store item.

Well, I flushed it out and then the core started leaking. I figure maybe it had leaked before and they put "stop leak" in it. That plugged the hole but also clogged the passages. Once I flushed it, then the leak became evident. I have a new one on order. Luckily I won't need it until about November.

Mike