REMOVE/REPLACE THE HEATER CORE IN A 1970 CUTLASS SUPREME CONVERTBILE

My dad was a convertible nut.  In 1951, at age 13, he bought his first car:  a ’48 Plymouth coupe.  Owned it for 6 months.  Hated it.  Didn’t buy another Chrysler product for 30-some years, and he hated that one too.  From then on, it was a run of Chevy convertibles up until he became a dad in 1968.  I got to hear about those convertibles growing up.  Combined with the Oldsmobiles we had when I was a kid, I guess that’s what steered me towards wanting a classic Cutlass convertible.

I bought the subject of this blog in April 1997.  I was looking forward to the occasional cruise with my dad and maybe even doing a repair or two with him where I was in charge and he wasn’t swearing and saying “you’re doing it all wrong”.  You know, a father and son bonding moment talking about the finer points of ignition points.  He died in July 1997, and he only got to take it for a spin with me once.  He liked the engine; “It’s got some scoot” was his comment.

One of the first repairs I diagnosed, on the day I drove the car home, was the heater core.  This was pretty easy to figure out, as the window would steam up a bit and you’d smell anti-freeze anytime you turned the heat on.  Fast forward to 2014.  The heater core STILL hasn’t been done because I’m lazy that way.  And because I’ve heard horror stories, starting with my dad, about how much of a bear a heater core job is.  With the dashboard off the car to replace the top switch, it’s time to roll up the sleeves and take on the dreaded heater core.

You know what?  Everything you’ve ever heard about heater cores is a bunch of horse feathers.  Other than being time-consuming, it was a pretty easy task.

The main reason I brought up my dad is because of the safety tips he gave me while working on a car.  It’s easy to get lackadaisical, but this is a 3800 pound hunk of iron that can kill you if you are careless.  As this job requires jacking up the car and yanking on hoses (heh), it’s a great time to bring up some of those safety tips.

TOOLS YOU’LL NEED

• A ¼” socket set, specifically the ¼”, 3/8”, and 5/16” sockets
• A 1/2″ or 3/8” socket set, specifically with a 7/16” and 9/16″ socket
• A 7/16” combo wrench
• A large catchpan
• Jack stands
• A good floor/garage jack
• Wheel chocks
• Don’t forget your towel
• Baggies, sharpie, flagging tape for sortin’ and writin’ stuff up

PARTS

• Heater hoses (optional, depending on condition of current hoses)
• Hose clamps for 5/8” and 3/4″ hoses (optional, depending on condition of current clamps)
• Heater Core (optional, you may want to rebuild the original if the car can sit idle for a week)
• Heater Case Gasket Kit (available from most restoration parts suppliers)
• Firewall Insulator (if you’ve got the heater case off, might as well replace it)
• Vacuum hose (different sizes, keep your pants on and we’ll get to it)

BEFORE YOU TRY THIS AT HOME:

Remove the Dashboard, Part I and Part II:  Many how-to guides skip this part or only have you remove a couple of things.  I can’t tell you what it would be like trying to tackle the heater core with only some of this stuff removed, but my guess is that it would not be easy.  You’d have little room to maneuver and precious little light to see.

1.  Drain Radiator.  If you’ve got the original Harrison radiator, there should be a petcock on the RH side near the bottom of the tank.  Put a large catch basin underneath; I find the big ones for doing an oil change work perfectly.  Open the pet cock and prepare for splashing, it should just be on there hand-tight.  There’s probably a better way of draining the radiator, but I don’t know what it is.

Ah, sweet lemonade. See what I mean about it being a mess to drain a radiator?

2.  Disconnect A/C Reducer Hose Hold-down Clamp.  This clamp holds down the line that takes warm refrigerant to the condenser.  I think I got the name right.  I’m not working on the A/C so I’m not looking it up.  It’s hiding a bit underneath the line that takes the cold pressurized refrigerant to the evaptorator.  There’s a screw attaching the hold-down to the plastic inner fender.  Should come off easy.

Here’s the two hold-down clamps you’ll need to remove the screws for.

3.  Disconnect Heater/Block Reducer Hose Hold-down Clamp.  This clamp helps route the aforementioned hose around the evaporator box.  Might as well remove the screw while you’re up here.

4.  Loosen 2 Rear Lower RH Outer Fender Bolts.  These are what holds the dog leg of the front fender to the car body.  Find the “Cutlass” emblem and look down; they’re just in front of the rocker panel.  No need to remove them; just loosen them.  It’ll be obvious why in a few steps.

5.  Loosen/Remove RH Inner Fender Bolts.   Just in case these buggers stick, get them loose when the car is resting on the wheel instead of on a jack stand.  As my dad would say, don’t jostle a car that’s on a jack stand.  There’s a lot of these bolts; 13 if I remember the count correctly.  There’s 4 that are accessed from under the hood, at the front; 5 that run  the outer edge of the wheel well opening; 2 that secure the top of the inner fender to the outer fender (you can see where the tips poke through from the engine compartment) and 2 that are in the back and behind, securing the inner fender to the frame.   The last 2 cannot be reached until the wheel is off, so don’t worry about them.   The rest are pretty easy to get at.  Use a breaker bar if they put up a fight.

Four of the thirteen bolts holding down the inner fender. View from RH front corner, looking towards the firewall.

6.  Remove RH Front Wheel.  If you don’t know how to remove a wheel from a car, stop now.  Do not do ANYTHING else until you’ve taken a basic car maintenance class at the local park district or community college.  Then come back and continue reading.  Otherwise, here’s some of my dad’s safety tips:

• Put the emergency brake on and chock the other three wheels.  Did you know that wedges cut to make a hinge when falling a tree make great chocks?
• Only jack on the frame to lift the car; NEVER the suspension.
• Position the jack stand on solid, level ground.  Make sure the pin/ratchet is locked.
• Leave the floor/garage jack in place even after the car is resting on the jack stand, unless it’s gonna get in your way.
• When the wheel is off, put it underneath the frame right behind the jacking point.  The wheel is your failsafe should the jack stand fail.

7.  Remove The 2 Pesky RH Inner Fender Bolts From Step 5 That You Couldn’t Reach Because The Tire Was In The Way.

8.  Remove RH Inner Fender.  It’ll quickly be obvious why you needed to loosen the dog leg of the outer fender back in Step 4.  By moving that part of the fender outwards, you can work the inner fender around the lip of the outer fender.  Then the inner fender should pop right off.  As an added bonus, you can easily clean all the debris and dirt that builds up behind the dog leg.  Ever wonder why the lower front fenders of GM cars from this era rot?  Take a look back there after the inner fender comes off and you’ll have the answer.

9.  Remove Heater Case Nuts.  Look at all the room you have now.  All this work to get the fender off et al. is really just to get at one of the four nuts holding the heater case to the car.  All are easy to find.  The two hardest ones to get off are the upper right, which is sort of behind the A/C evaporator pipe, and lower left, which is kinda behind the transmission dipstick.  Don’t bother with a socket. These are self-threading nuts and they come off easily with a box wrench.

Locations of the 4 heater case nuts. In case you haven’t guessed, this is not a frame-off restoration.

10.  Put The Wheel Back On.  This is another dad safety tip.  His reasoning:  if you are goofing around inside the car, best to have the car as stable as possible.  It adds some extra time to the project, but the alternative is to risk having the car fall off the jack stand while you’re yanking on the heater case trying to get it out.  And it’ll be easier to get the heater hoses off if the car isn’t an extra 8 inches in the air.

11.  Disconnect Blower Motor & Compressor Hold-in Relay Wires.  These wires will be in the way while you’re removing the heater hoses.  Best to just move them so you don’t break them.

12.  Remove Heater Hoses.  Loosen the heater hose clamps and slide them down the hose to get them out of the way.  Note how the clamps are positioned; that’s the only angle of approach that makes sense if you need to get a screwdriver or socket on the clamp.

Every DYI I’ve read about heater cores says that getting the hoses off is the hardest part.  I cannot second this.  Here’s what I did:  I grabbed each hose, just below where the heater core throats are, wearing a pair of leather work gloves.  This is another dad safety tip, this one to prevent you from getting tetanus when you rip your knuckes open on sharp, slightly rusted sheet metal.  Works well on spark plug jobs too.   Twist the hoses clockwise and counter-clockwise until they ‘pop’ loose and spin with your motion.  Then they should come right off the heater core throats.

Despite all the horror stories and tales of terror, this took me all of 3 minutes to do.  So there.

You’re done on the outside of the car.  Time to head back to the interior. Other online guides that I’ve read aren’t very clear about what needs to be removed so the heater case comes out.  Despite the blurry photos, I will be very clear in telling you what needs to come off.  Especially since the guys that wrote the service manual took the day off when it came to this part.  Seriously.  Here’s the entire procedure as outlined in the Oldsmobile Chassis Service Manual, page 1C-8:  “The heater core can be removed after removing the heater case assembly.”  Gee, thanks guys.

13.  Remove the Defroster Adapter.  Say that ten times fast.  There’s one screw that holds it on, smack dab in the front.  Remove the cardboard ducts and the adapter comes off.  Easy as pie.

Location of the defroster adapter screw.

14.  Disconnect Temperature Control Cable.  There’s one screw holding the cable assembly to the controller.  After that, lift the tip of the cable off the controller tab.  Done.

Removing the temperature control cable.

15.  Disconnect 2 Vacuum Lines.  The picture is blurry but the lines you need to remove are easy to find.  The first one is hooked up to the defroster control valve on the far LH side of the heater case.  The second attaches to the mode control valve on the back side of the case, facing the fire wall.  Knowing that this might be a problem, GM engineered a small nylon splicer in this hose.  (But they didn’t leave access to get at the convertible top switch. Huh.)  Remove the hose at this splice.  Don’t forget to use flagging tape to label the hoses.

16.  Remove 2 Screws Holding Heater Case to Firewall.  There’s one screw right of center top, and another right of center bottom.

Location of upper heater case attaching screw.

Location of lower heater case attaching screw.

17.  Remove Heater Case.  Congratulations, you are now ready to remove the heater case.  Assuming you were careful and did not bend or deform the heater core throats, the case should come off with a wee bit of wiggling.  Put a couple old towels down in case you get any drippage.  Better to ruin an old towel than the carpet.  Though if you neglect the heater core for 17 years like I did, the carpet may be ruined already.  I got lucky, sort of.  Only the firewall gasket was ruined.  That’s OK.  It’s 44 years old and needs to be replaced anyhow.  This is what is commonly referred to in the antique car hobby as a MAW:  Might As Well do it with other stuff out of the way.  After all, when’s the next time you’re going to have the heater case off the car?  2084?  That’s when the Robotron invasion happens, we’ll be too busy panicking to worry about fixing an old car.

18.  Remove Temperatue Controller.  Now we get to the meat ‘n taters of the project.  This controller operates a door that regulates the mix of warm air from the heater core and cool air from outside/A/C evaporator.  Pop the spring off the controller.  Next, remove the three screws; you may have to move the control around a bit to access them all.  With the screws out, wiggle the control and it should come right off.

Location of screws for temperature door control.

Here’s a tip to help you align the control when you reassemble the heater case:  use a sharpie to outline the control on the case.  When it’s time to reassemble, just line it up with the template you drew.  If you are worried about defacing your heater case, wipe the sharpie off with some acetone when done.

18.  Remove Heater Core Cover.  Flipping the heater case over so you are looking at it from the back, you’ll see 8 screws on the side with the heater core.  The 4 around the edges hold the heater core cover to the heater case.  The other 4 hold straps that attach the heater core to the cover.  You can take them all off right now, if you so choose.  Doesn’t much matter.

Heater core cover and heater core strap screws. Magenta arrows indicate cover; red arrows indicate straps.

And there she is.  Your wonderful, leaking heater core.

Yeah, I’d say your heater core is bad.

If you look closely, you’ll see a metal flange holding the two throats of the heater core together.  The flange was put on Harrison heater cores to hold the throats in proper alignment for installation.  Aftermarket cores won’t have it.  Aftermarket cores are also made out of thinner materials.  An original core will also have the Harrison logo stampted on the “bottom”.  Now it is decision time:  should you have the old heater core rebuilt?  If you have a radiator shop nearby, explore the option.  It’ll cost a bit more than an aftermarket core, but it is likely to last just as long if not longer.  Might be worth looking into, so that years from now, the next person to take it off will find the original heater core and think it lasted a bajillion years.  It’ll be awesome.  You’ll blow their fucking minds.  Unless they’re running in panic from the Robotron invasion.

Of course, you’ll reverse all the steps to put things back together.  DO NOT OVERTIGHTEN THE HEATER HOSE CLAMPS!  Refer to the post on radiator replacement for refilling the engine coolant.

Here’s a list of some of the MAW mini-projects you can do with the heater case out:

• Replace the vacuum lines, esp. the one on the back of the heater case.
• Replace the firewall/under-dash insulation.
• Replace the heater hose clamps.
• Replace the heater hoses.  These things seem to last forever.  If your hoses look deformed, or proved to be impossible to remove, you should replace them.
• Replace the heater case gaskets.
• Wash and recondition the various parts of the heater case.  Acetone or a parts cleaner for metal.  Soap and water for plastic.