Reverse Flow a Heater Core? Pros and Cons

[azmusclecar]

I once saw or heard of reverse flowing the heater core to help flush contaminants out of it.
I see the hoses seem to be different sizes.

I'm repairing some cooling issues and thought I'd address this now for when winter comes.
I recently ran my heater to help lower radiator temps to get me home on a test drive.
I notice the supposed hot air was more warm air.

I don't need a blast furnace here in AZ, but just wondered if others have heard, tried and either dismiss the idea
or have had success with it.

 

[fleming442]

I did it, the earth is flat, and I still say it ain't directional. Flamesuit engaged...

 

[69hurstolds]

I did it, the earth is flat, and I still say it ain't directional. Flamesuit engaged...

You are correct. Most heater cores are only "directional" because of the hose size and routing. In other words, the engineers just CHOSE the flowpath the heater core would have. It makes no real difference which way the water flows through it. Same with your radiator. As long as the water is flowing through the unit and air is flowing across the fins, the heat transfer will occur. If you hook it up "backwards" you will still get heat from it.

Now, when it comes to flushing, yeah, you probably would have better luck backflowing a heater core or radiator if you suspect it having trash in it. It's just a heat exchanger. But also, it's going to clog up after a while and even backflushing may not clear it out enough.

If you have the time, it's SO easy to change out a heater core on the A/G bodies with A/C the way they're set up. Sure, a bit of a PITA, but you can do it all from under the hood. Nowadays there's many more made out of aluminum vs. brass unless you can find a GM replacement. I think I might have seen like 1 brass core aftermarket. Nothing wrong with aluminum, but make sure you get a quality one. You won't be able to tell the difference in the car between the two materials anyway. Just make sure it's a good, quality unit whatever it's made out of.

For sh*ts and giggles....

GM part number is 3037689 or equivalent. But....they're super scarce.

 

[69hurstolds]

Nice little writeup here to give you an idea on the difficulty factor on doing this if you decide to tackle it now or next spring or whenever or never.

https://montecarloforum.com/forum/rwd-tech-guides-70-88-63/g-body-heater-core-replacement-18270/

 

[azmusclecar]

Nice little writeup here to give you an idea on the difficulty factor on doing this if you decide to tackle it now or next spring or whenever or never.

https://montecarloforum.com/forum/rwd-tech-guides-70-88-63/g-body-heater-core-replacement-18270/

Ahhhhhh, that's not too bad...........wow I thought it would be a lot more difficult.

Thanks for the link..........I was just considering a reverse flow but now I see it may just be worth it to go with a new core.

From what I see in the old radiator I imagine it's just as bad in the heater core. I just bought a new aluminum radiator
since the old one just wouldn't flow to keep the temp down. I'll shop around for a core, but in the meantime I can always
do a reverse flow and see what happens.

 

[pontiacgp]

I did it with my last jeep, poured vinegar into the heater core, drank 2 beer then back flushed it, I repeated it a few times and took a cab home....

 

[airboatgreg]

Why?
Flush iy properly out and be done with it for 2 years

 

[403Olds]

I had a Roadmaster that I took the heater hoses off, took a garden hose to the heater core and flushed it both ways till it ran clear, then put the heater hoses back on. I did that each fall, it gave me good heat all winter.

 

[69hurstolds]

I had a Roadmaster that I took the heater hoses off, took a garden hose to the heater core and flushed it both ways till it ran clear, then put the heater hoses back on. I did that each fall, it gave me good heat all winter.

But what if you didn't? What if you left it alone for say, I dunno, nearly 40 years? What works for YOU may or may not work for other people. If you're starting in a good place, it's easier to keep it there. azmusclecar is starting out with a car that has sat for Lord knows how many years. So, there's that. Working with an unknown situation here.

I would agree, a backflush couldn't hurt. It's virtually free with nothing but a couple of hose connections to deal with. What's the worse that could happen? If water flows through it, that's a good sign. The thing springs a leak and he has to change it out anyway? Or it just cleans up as best as possible and run it if it holds?

There's also the question of the "air" side that you can't see. Does air blow out the vents strong going through the heater core? If the air side is fouled up, you have to consider that as well.

 

[oldsmobile joe]

this is my story and I'm sticking to it.
our heater cores are not directional, well kind of. let me explain. our heater hoses are two different sizes. the larger one is the supply side and the smaller one is the return side. and the reason for this is that the hot side holds more volume, coolant expands when heated. there for the cold side is smaller, coolant contracts when cooled.
can you switch direction, sure you can, but you will also need to change the nipples on the engine accordingly.

nothing is ever for sure in life. i don't know what it had for coolant, was it 50/50 anti-freeze/water, was the water distilled or tap, soft or hard. being an arizona car, my concern is the water was hard tap water and the core is restricted from hard water deposits. try running some CLR through it. you have nothing to loose. or buy a new core, it might be easier in the long run.