Heater doesn't work so good - 74 Duster

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Loggato

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Is everyone satisfied with the heaters in their A-bodies?

I have 2 problems with mine.

1. hardly any air flow (fan on high)
2. Doesn't get very hot

I think the second can be solved with cardboard in front of the radiator (engine temp does not get very high)(yes, new thermostat), but before I start to diagnose the first, I'm wondering if anyone else has the same opinion.

Thanks
 
does the car have a/c? the valve may be stuck in a closed or semi-closed position.
heater core plugged,reverse flush.
hoses soft and collapsing.
 
remove both heater core hoses at the engine. blow throw there with a garden hose and nozzle on the end. Flush the core, back and forth so it's clear both ways. Be prepared to turn your temp down :)
 
I have 2 problems with mine.

1. hardly any air flow (fan on high)

That sounds like a clogged heater core or leaves or other debris blocking it. If it’s clogged up, a reverse flush should help; otherwise open the case up and clean it out.

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2. Doesn't get very hot

I think the second can be solved with cardboard in front of the radiator (engine temp does not get very high)(yes, new thermostat), but before I start to diagnose the first, I'm wondering if anyone else has the same opinion.

Thanks

I’ve never had heating issues with any 60’s/70’s Mopar I’ve owned both brand new and well used. I would find out what the problem is with the engine temp- which affects the temperature of the heater core! “Engine temperature does not get very high” - incorrect thermostat, collapsed upper or lower hose, clogged radiator, does the motor need a thorough flushing to get all the built up crap out of it? Got a thermal gun to check radiator and engine temps. At a minimum check the temp of the coolant with a decent thermometer. A piece of cardboard in front of the radiator is just a bandaids fix.
 
does the car have a/c? the valve may be stuck in a closed or semi-closed position.
heater core plugged,reverse flush.
hoses soft and collapsing.

remove both heater core hoses at the engine. blow throw there with a garden hose and nozzle on the end. Flush the core, back and forth so it's clear both ways. Be prepared to turn your temp down :)

I have a thread on here about the car overheating. In short, It's got new heater hoses, and I flushed the whole system MANY times. I do not believe it to be a coolant flow issue, although I wont discount that thought. Car does not have A/C currently and also the flaps inside the heater box are all working.

It actually sounds like there isn't much resistance at the fan.. I'm going to pull it and see if there is a bunch of blades missing.
 
Agree, but I like to start from scratch on these problems.

I'm guessing (so far) that everyone's heaters work great and mine does indeed have an issue?
My '74 Duster will heat you out. I've had several A-bodies I've driven in the cold, snowy winters and heat isn't a problem
 
It actually sounds like there isn't much resistance at the fan.. I'm going to pull it and see if there is a bunch of blades missing.
This could be a possibility but unlikely, maybe your fan hub cracked and the fan motor is just freewheeling.....if you can grab your heater hoses with your hands and not feel the heat you have problems, could be as simple as leaves and such blocking the heater core.
 
Are you sure you have the proper amount of coolant in your cooking system. If your low on coolant it can cause a little to no heat situation ..
 
This could be a possibility but unlikely, maybe your fan hub cracked and the fan motor is just freewheeling.....if you can grab your heater hoses with your hands and not feel the heat you have problems, could be as simple as leaves and such blocking the heater core.

My fan sounds like it's freewheeling, but there is still some air movement. I'm anticipating little mice bite marks on the blades!
 
The radiator guy said it was clogged with BarsLeak, or a similar leak stopper. It took a while to get the heater core flushed out to, and I'm not convinced that the heater core is flowing that well. I have another one, but it's with the AC HVAC box that I bought for when I convert this car to an A/C car.

The block has always flowed fairly clean water through it. Fortunately the issue is resolved.
Me, if you go this far to check the fan, I would change out your heater core, remember you are not convinced that the heater core is flowing well...….
 
Me, if you go this far to check the fan, I would change out your heater core, remember you are not convinced that the heater core is flowing well...….

Agree. My concern is If I'm this far into it, I'd like to just install my A/C heater box in preparation for A/C next summer. But then I would need to make changes to the firewall to accommodate. I'll need to mull that over.
 
Make sure your heater hoses are hooked up right-I know most people say it doesn't matter. I've never seen a service manual, that says it doesn't matter. They have pictures of each body style with arrows in the hoses and where they are hooked up-so apparently it does matter. In the mid 70's I was driving my 68 GTS as a daily driver, winter also. I couldn't afford a new heater core so I would just change the whole heater box, hoping it was better. It was like in January-cold, and I had just changed the box. Heater blew out just barely warm air. Buddy asked why my heater didn't work any better. I told him I had just put in a different heater box-he asked-did I get the hoses on right? I changed hoses around, and I had hot heat.
 
Mopars either have too much heat or none it seems. Replace the heater core and be done with it. Flush never seems to get it back the way it should be. The new replacement heater cores are much more efficient and have about double the fins as the original.
Yes it does matter which way the hoses go on. I cant explain why but it does make a difference.
 
Heater core flow test
Grab both heater hoses with engine running and at operating temp. they should be roughly the same temp. One cool, one hot-core is plugged.

To flush core, pull both hoses. using a 2-3 foot hose on one side and another in a jug to catch what blows out.
pour a couple cups of water in hose and follow with a blast of compressed air. twice in each direction. the jug should be full of debris.
 
As many of the replies have mentioned, flush the core by itself. The way they're made and positioned makes them a "dirt trap." The flow rate is lower, vs the rest of the system. The top enter and exit causes dirt to settle in the bottom of the core and slowly block tubes over time.

I've flushed a few small blocks, several times, draining the block, etc. Then disconnecting the core hoses at the block and doing it w the garden hose yields a big blob of dirt into a 5 gal bucket and you have heat.
 
Sounds a lot like the air door not coming open or inlet opening is blocked. Getting into these things under dash is a good line of work for a contortionist. Hose hook up matters because thermal convection helps pull flow through the core evenly. Hot water goes to the lower half of horizontal tubes, rises up on the small tank end and comes back across the upper set of tubes. It doesn't work too well trying to push hot water downward through the restriction of the core tubes, steam bubbles tend to restrict water flow.

oer-copper-brass-heater-core-13.png
 
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On both the engine and the heater core, there is a large port and a smaller port. this is a slant 6 car. unless for some odd reason the big hose goes to the small port, they seem to be correct. I haven't been able to find a diagram showing which hose goes specifically into which port.
 
That would be correct. Large hose and tube is return to inlet side of pump along with thermostat bypass and the lower radiator hose. The small tube is hot water plumbed from the head ahead of the thermostat. As stated, a cold return tube indicates a blockage, either through the core or the hot water control valve.
 
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