Pic of heater hose connections 1993 7.4?

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someotherguy

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The heater core must be leaking on my freshly-acquired '93 C3500 7.4 - the return line is cut and I guess the nipple on the radiator tank is plugged with some unidentifiable object.. but the supply line with a quick-connect style aluminum end is just hanging with no apparent mate. I don't see a pipe plug or anything other than one on the water pump next to the bypass hose to the intake.. so I can't really make out where it used to attach. There's a tab on the hard part of the line that looks like it mounts to a bracket with a single screw, but I can't make out where it used to live. This is a 1993 model 7.4 and doesn't have the plate under the throttle body for the heater hose attachment/adapter like the earlier TBI 7.4's if that helps.

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Richard
 

Schurkey

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It'll be in the '93 Service Manual. Since I can't find a link to the '93, here's the '94 which should be the same.
www.mediafire.com/file/7d5v4lasgb495ta/1994_NATP_9431_1994_CK_TRUCK_SERVICE_MANUAL.pdf/file


Page 1A-17. Hose attaches to right-rear of intake manifold, kinda like small-blocks. The tab on the heater tube attaches to a bracket on the rear of the cylinder head.

The Dorman quick-coupler for the heater system is strongly recommended. Mine's 20+ years old, and looks like new. The GM originals rot-out.
 

someotherguy

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Thanks; I'll pull the air cleaner and see what's going on - certainly a pipe plug on the intake side. Maybe the core is OK but the connector went bad as most originals do, very familiar with that. Just hadn't owned a TBI big block before, only Vortecs.

Richard
 

454cid

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Interesting, I would have assumed it would be in the same spot as the vortec as that pretty well follows the carb placement that I've seen on GM v8s.
 

someotherguy

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Interesting, I would have assumed it would be in the same spot as the vortec as that pretty well follows the carb placement that I've seen on GM v8s.
Haven't had to replace any heater hose quick connects on a Vortec big block so I've never even looked at the thing. :) Only replaced them on a few TBI small blocks, and run across ones that had already been replaced. So this whole TBI big block thing is new to me. The '95 3500HD 7.4 I had previously had no coolant leak issues other than the radiator which had a close meeting with the fan...

Richard
 

454cid

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Haven't had to replace any heater hose quick connects on a Vortec big block so I've never even looked at the thing. :) Only replaced them on a few TBI small blocks, and run across ones that had already been replaced. So this whole TBI big block thing is new to me. The '95 3500HD 7.4 I had previously had no coolant leak issues other than the radiator which had a close meeting with the fan...

Richard

What I mean is that I'm suprised it wasn't up front, like my Chevy 454, Buick 430, and Buick 350, and earlier carbed Chevy engines I've seen online. The rear of engine port is kinda weird to me. I guess it could mean a shorter run of hose, which wouldn't be bad.

Does the "new" truck have the tall radiator that requires the seemingly uncommon tall brackets?
 

packer0440

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When they switched to the TBI manifold (1991), the coolant port was moved to the passenger rear of the intake like the small blocks. Earlier Mark IV big blocks have the coolant going through the TBI spacer which then goes to the heater core.

I’ve fixed one on my 1992 BBC, and luckily they left enough room to use an EZ-out on the fitting that had snapped in half. Haven’t had any issues with the Dorman replacement.

If yours currently has a brass/metal plug, it should be an easy job to just put a new one in. The intake is cast iron so it’s less likely to be seized.

As mentioned above, that hose is designed to be secured by a screw to a metal bracket that’s on the back of the head but zip ties do the trick
 

someotherguy

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If yours currently has a brass/metal plug, it should be an easy job to just put a new one in. The intake is cast iron so it’s less likely to be seized.
Seized like it's f'in welded. Just a handy FYI. Wish it wasn't..I'm ready to blow it up.

Chiseled the remains out, ran a tap through it, put a pipe plug in there (tight fit) with some pipe dope on it. Leaks. FML

Richard
 
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