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Fixing a leaking Corvette heater core

Fixing a leaking heater core

Keith Keplinger - October 27, 2011 10:00 AM

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We began by carefully removing the passenger dash trim and glove box panel.

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The center A/C register came out followed by the center gauge stack. Just set this off to the side; no need to disconnect everything.

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With the ductwork removed, we were getting closer to the core. This was starting to look easy.

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Unclip the vacuum line and place the hose out of the way. Remove the underdash light that’s attached to the heater box. It was at this point that we remembered that you should disconnect the battery before starting any major project. Lesson learned.

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Remove the two lag screws along the bottom edge of the heater box. The long one goes on the left, the short one to the right. Remove the right hand lag screw along the top of the heater box, and make note of the stud on the left side. We left it in place while we finished up the interior stuff.

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Remove the two screws that connect the heater box to the center ductwork and the one screw on the top edge of the ductwork next to the heater box.

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The “Mystery Nut” – GM did a good job of hiding this one. We removed this relay for better access and found the mystery nut hiding under the wiring hold down strap!

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Back inside, slip the compression washer off of the heater cable, and remove the holding screw.

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It was time to get under the car. Carefully jack the car up and place it securely on jackstands. Removing the wheel gives you room to move around. Have a small pail handy to catch the radiator fluid. The first worm clamp was relatively easy to remove. The second was more of a challenge. We cut the hose as close as possible to the heater core, then rotated the remaining piece of hose and clamp 180 degrees and removed it. You can’t get the heater box out with the hose clamp in place.

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The vacuum lines for the heater door must be disconnected. Both lines are located on the back side of the heater box. The line on the inside of the box is a straight line; simply reach inside the box and pull it off. The line on the outside of the box has this neat little “retainer” feature. Slip the bottom of the loop up, then the retainer and line will slip off of the actuator.

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Carefully remove the heater box by rotating it down, and twisting it to the right.

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Yep, there was no doubt that we had found the leak.

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Remove the screws on the clamp assembly and remove the four screws holding the heater core assembly to the heater box.

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There are two band clamps holding the heater core to the assembly. Remove the four screws and gently work the heater core loose.

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A side-by-side comparison of the original core and the replacement part from Zip Products shows few differences in the two parts.

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There’s an interesting date mark inside the heater box. August 23, 1971, maybe?

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After thoroughly cleaning everything and test fitting the new core into the bracket, there was a slight rubbing/tightness. Not wanting to force the new core into place, we carefully clearance the bracket. Fit like a charm!

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Tighten the screws on the two retaining clamps. An extra set of hands came in handy to hold everything in place and tighten the screws.

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Install the pipe clamps using the two brackets and three screws.

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Place the heater core assembly into the heater box and secure with the four screws.

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There was an indication that at one time, a strip of foam was along this edge. Most of it had long rotted away. Order the correct foam strip when you order the heater core. We used a piece of household self-stick foam.

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Wiggle the heater box back into place. Before getting it too far in, re-attach those two vacuum lines, the ones you can’t see back there!

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Back into the engine compartment, slip the wiring hold-down back onto the stud and tighten the bolt. Having someone inside to make sure that the heater box was tight against the firewall is a huge help! Replace the wiring, re-bend the hold down, and reattach the relay.

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Slip the heater cable back into place, slide the compression washer back into place and re-attach the cable hold-down screw.

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Reattach the vacuum line located on the passenger kick panel. Note the retaining loop.

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Finish fastening the duct to the heater box with the two screws.

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There are three screws that hold the heater box to the firewall. The large one goes bottom left, the two small ones are on the right side.

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Cut the old clamped end off of the hose to give a clean piece of hose for the new clamps to bite into.

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We installed the larger hose first, and clamped it into place with a new hose clamp. The smaller hose was next. Nice and neat.

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Back topside, reinstall the passenger under-dash light.

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Reinstall the rest of the dash. Top off the radiator, and check for leaks. Since there were none, celebrate with dry feet!

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When Ralph and Leah Meder bought their 1973 Corvette, they knew that it was going to be a project.

They were prepared that the journey of restoring it back to being a good looking driver was to be part of the fun.

It was during one of those first drives that Leah noticed her feet getting wet and warm. Ralph was noticing the temperature gauge beginning to rise. “Heater Core” are words that strike fear into the hearts of most owners, as we’ve all heard the horror stories of the difficulties of fixing this common problem. Undaunted, Ralph and I set out on a warm Saturday morning to do the “HeaterCore-ectomy”.

 

For Your Information:

 

Zip Products

(800) 962-9632

www.zip-corvette.com

 

We began by carefully removing the passenger dash trim and glove box panel.

 

The center A/C register came out followed by the center gauge stack. Just set this off to the side; no need to disconnect everything.

 

With the ductwork removed, we were getting closer to the core. This was starting to look easy.

 

Unclip the vacuum line and place the hose out of the way. Remove the underdash light that’s attached to the heater box. It was at this point that we remembered that you should disconnect the battery before starting any major project. Lesson learned.

 

Remove the two lag screws along the bottom edge of the heater box. The long one goes on the left, the short one to the right. Remove the right hand lag screw along the top of the heater box, and make note of the stud on the left side. We left it in place while we finished up the interior stuff.

 

Remove the two screws that connect the heater box to the center ductwork and the one screw on the top edge of the ductwork next to the heater box.

 

The “Mystery Nut” – GM did a good job of hiding this one. We removed this relay for better access and found the mystery nut hiding under the wiring hold down strap!

 

Back inside, slip the compression washer off of the heater cable, and remove the holding screw.

 

It was time to get under the car. Carefully jack the car up and place it securely on jackstands. Removing the wheel gives you room to move around. Have a small pail handy to catch the radiator fluid. The first worm clamp was relatively easy to remove. The second was more of a challenge. We cut the hose as close as possible to the heater core, then rotated the remaining piece of hose and clamp 180 degrees and removed it. You can’t get the heater box out with the hose clamp in place.

 

The vacuum lines for the heater door must be disconnected. Both lines are located on the back side of the heater box. The line on the inside of the box is a straight line; simply reach inside the box and pull it off. The line on the outside of the box has this neat little “retainer” feature. Slip the bottom of the loop up, then the retainer and line will slip off of the actuator.

 

Carefully remove the heater box by rotating it down, and twisting it to the right.

 

Yep, there was no doubt that we had found the leak.

 

Remove the screws on the clamp assembly and remove the four screws holding the heater core assembly to the heater box.

 

There are two band clamps holding the heater core to the assembly. Remove the four screws and gently work the heater core loose.

 

A side-by-side comparison of the original core and the replacement part from Zip Products shows few differences in the two parts.

 

There’s an interesting date mark inside the heater box. August 23, 1971, maybe?

 

After thoroughly cleaning everything and test fitting the new core into the bracket, there was a slight rubbing/tightness. Not wanting to force the new core into place, we carefully clearance the bracket. Fit like a charm!

 

Tighten the screws on the two retaining clamps. An extra set of hands came in handy to hold everything in place and tighten the screws.

 

Install the pipe clamps using the two brackets and three screws.

 

Place the heater core assembly into the heater box and secure with the four screws.

 

There was an indication that at one time, there was a strip of foam along this edge. Most of it had long rotted away. Order the correct foam strip when you order the heater core. We used a piece of household self-stick foam.

 

Wiggle the heater box back into place. Before getting it too far in, re-attach those two vacuum lines, the ones you can’t see back there!

 

Back into the engine compartment, slip the wiring hold-down back onto the stud and tighten the bolt. Having someone inside to make sure that the heater box was tight against the firewall is a huge help! Replace the wiring, re-bend the hold down, and reattach the relay.

 

Slip the heater cable back into place, slide the compression washer back into place and re-attach the cable hold-down screw.

 

Reattach the vacuum line located on the passenger kick panel. Notice the retaining loop on the vacuum line.

 

Finish fastening the duct to the heater box with the two screws.

 

There are three screws that hold the heater box to the firewall. The large one goes bottom left, the two small ones are on the right side.

 

Cut the old clamped end off of the hose to give a clean piece of hose for the new clamps to bite into.

 

We installed the larger hose first, and clamped it into place with a new hose clamp. The smaller hose was next. Nice and neat.

 

Back topside, reinstall the passenger under-dash light.

 

Reinstall the rest of the dash. Top off the radiator, and check for leaks. Since there were none, celebrate with dry feet!

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