Quick Heater Core Swap Question ...

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Oct 28, 2004 | 11:54 AM

CameronAdams

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Junior User

Joined: Sep 2004

Posts: 59

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From: Seattle WA

Quick Heater Core Swap Question ...

Seems like now that it's getting cold, everyone online's doing their heating systems! I'm midway through my own heater core swap, (already read all the tech articles & postings) and I've got one real easy question I was hoping someone would help me out with:

I've got a '77 F250, and when I bought it, the heater hoses were chopped off at the firewall. I'm putting in a new heater core, and I don't know which of the 2 core sides/connections (on the engine side of the firewall) is for the bypass hose and which is for the heater/inlet hose.

I've got a Haynes manual, and it's about the most useless thing I've ever used! It doesn't show which hose goes where. It doesn't even cover the heater core swap as it relates to AC-equipped trucks, stating "..The following procedure is intended for vehicles without air conditioning. The addition of air conditioning complicates the procedure to the point where it is beyond the scope of the home mechanic..". I guess I probably shouldn't have even had the nerve to buy their lame manual, huh? What was I thinking?...

Anyway, if someone could enlighten me here, I'd be very happy, and a whole lot warmer. Thanks!.. Cameron

Oct 28, 2004 | 01:05 PM

firstonraceday

Laughing Gas

Joined: Dec 2000

Posts: 781

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From: East Texas

My '77 is non-A/C so I don't know if A/C trucks are routed like this. But, on mine the hose from the core tube toward the driver side runs to the water pump. The other hose runs to the block. That's on a 351M.

Perhaps this will help, if not I know one of the FTE members with an A/C truck will come along with good information.

Oct 28, 2004 | 01:16 PM

krewat

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Joined: Jul 2002

Posts: 42,561

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From: Long Island USA

Quote:

Originally Posted by CameronAdams

I've got a '77 F250, and when I bought it, the heater hoses were chopped off at the firewall. I'm putting in a new heater core, and I don't know which of the 2 core sides/connections (on the engine side of the firewall) is for the bypass hose and which is for the heater/inlet hose.

I don't remember which way my '74 was, but if the tubes in the core are vertical, make sure the top side flows back to the engine, that way you won't get an air bubble in the core - if the tubes are horizontal and there is no place for air to collect, it doesn't matter which way you hook it up.

Quote:

Originally Posted by CameronAdams

I've got a Haynes manual, and it's about the most useless thing I've ever used! It doesn't show which hose goes where. It doesn't even cover the heater core swap as it relates to AC-equipped trucks, stating "..The following procedure is intended for vehicles without air conditioning. The addition of air conditioning complicates the procedure to the point where it is beyond the scope of the home mechanic..". I guess I probably shouldn't have even had the nerve to buy their lame manual, huh? What was I thinking?...

What they mean is that for the average home mechanic, A/C work is beyond their range - you have to disconnect the A/C hoses - if you know something about A/C and have the right guages, you can do the work yourself - of course, with Freon, that' s illegal now anyway

Oct 28, 2004 | 03:03 PM

dfisher1

Posting Guru

Joined: Jul 2001

Posts: 1,613

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From: Gainesville, FL

All,
The inlet and outlet are at the same elevation. It shouldn't make a bit of difference which one connects where. There is no valve, if there was, you would put it on the return.
Good luck,
KingFisher

Oct 28, 2004 | 03:26 PM

Redbob

Senior User

Joined: Oct 2001

Posts: 268

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From: North Texas

Good question!
It's never even occurred to me there might be a difference.

My truck ('78 Bronco 400 w/ A/C) has had the heateer core replaced twice by cutting out a chunk of the A/C case and hot-melting the plastic to seal it back up.
Seems to work OK, and saves several hours of removing stuff.

Oct 28, 2004 | 03:46 PM

krewat

FTE Leadership Emeritus

Joined: Jul 2002

Posts: 42,561

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From: Long Island USA

Quote:

Originally Posted by dfisher1

The inlet and outlet are at the same elevation. It shouldn't make a bit of difference which one connects where.

They are at the same elevation, but what does the core itself look like? Are the capillary tubes (no better name for them come to mind) vertical? if so and water flow is fed into
the top, that spells air bubble... ?

Oct 28, 2004 | 07:29 PM

ncl

Fleet Mechanic

Joined: Oct 2003

Posts: 1,371

Likes: 10

From: Green Springs, OH

I just replaced my heater core I have a 400 non a/c I it only took about 30 minutes to do it and thats pulling the whole blower assembly out from under the dash. From what I can see it doesnt matter which hose goes where,it is a normal in and out coil with aluminum fins on it. The antifreeze goes through a few passes and then out. You dont have to worry about an air bubble its not like youre dealing with a sealed hot water boiler like in a house The air will bleed out when it gets in the radiator out your overflow tube.Hope this helps.