Unusually thick heater core - The 1947 - Present Chevrolet & GMC Truck Message Board Network

shuttermutt · 11-03-2003, 09:03 AM

A couple of weeks ago the heater core in my 68 CST (327/TH400/Air) sprung a leak. Actually, it was plugged solid. When I ordered a "new" one, it was 1/2-inch too thin. I ordered another one from a different supplier. It was 1/2-inch too thin as well. Finally, I took it to my trusty radiator guy. He looked it up in his magic book and it showed that, essentially, my core was 1/2-inch thicker than it should be.

It's a Harrison unit, I'm 90% sure it's original, the factory clips that hold it in the black box fit it perfectly. What the heck is going on? I had my guy put a new core in between my tanks and I'm off and running again, but this is nagging at me. Why would mine be thicker than usual?

Blue Beard · 11-03-2003, 09:09 AM

Sounds like you have the wider radiator....which isn't uncommon.

There were two different sizes in the trucks......

The thicker one is probably just added another row...........

ckhd · 11-03-2003, 10:40 AM

It's the heater core not the radiator.

Someone else had the exact same problem a year ago or so, can't remember who. They couldn't find a core thick enough.

Hutch · 11-03-2003, 10:51 AM

shuttermutt
Maybe it is a heavy duty heater option.
Check the options on the glove box.
I am not even sure if this was an option though.
It may have been a dealer request for exteme climates like Maine.

Just guessing I am not really sure.

**MJN** · 11-03-2003, 11:21 AM

I had the same problem on my '72 Blazer, every core I bought was too thin and left and air gap around the edge. I finally bought a good used one and has been in there ever since, as of now no supplier makes the correct replacment heater core.

71GMC_3/4T · 11-03-2003, 11:34 AM

Yep, same thing here. I ended up with a bunch of polyethylene foam around mine to hold it in there. I don't know why the repro ones are smaller. Everything else is nearly the same, i.e., pipe sizes, lengths, and bends. I kept my old one in the box in case I ever want to have it fixed. It was in great shape except for a small pin hole.

I don't think yours is 1/2" bigger, I think someone at Harrison (or wherever) got a wrong dimension and it's been wrong for several decades...

shuttermutt · 11-03-2003, 11:36 AM

Mine wasn't so much that it left any kind of gap, but the clips that hold the core in place wouldn't tighten down. Instead, it just let the core flop around. The width and length were right, but the height (thickness) of the core was 1/2-inch off.

I've checked two different books and they both listed the core at 2-inches thick. Mine is 2-1/2 inches thick. I don't doubt that the quality of the "new" heater cores isn't very good (I had a Four Seasons that looked like it had been soldered in a washing machine it was so banged up and ugly), but they're the same thickness as what's called for in every book I've checked.

Hutch is probably right. There's nothing on the glove box sticker to indicate a special heater, but they may have just come that way for climates such as Northern Maine (where the truck was originally purchased). Either way, I'm thankful to have that extra thickness. Every little bit counts up here!

cableguy0 · 11-03-2003, 12:16 PM

thats odd i thought they were all the same regardless i guess im lucky my new core fit great after i replaced the one that had almost 2 pounds of sludge in it compared to the new one. yes i weighed it

oldcarbuff · 11-03-2003, 04:41 PM

my truck has listed as an option "deluxe air heat". the code is 4342aa (I think--its a little faded). I only have three options all together, so I suspect this may be a heavier duty heater, as the cheap sonofagun who bought my truck new only got a rear bumper and overload springs for his other two options

OCB

70 longbed · 11-03-2003, 05:05 PM

shuttermutt,

I had the same problem. I am sure that my core was original, and I could only find the thinner ones for replacement. I took mine to a radiator repair shop, and had it redone. It was a Harrison also.

Blue Beard · 11-03-2003, 11:14 PM

I have a new one in the box sitting in the garage.....

Very easy to come by..........

BobbyK · 11-04-2003, 03:05 AM

I replaced mine with your run-of-the-mill replacement.

It fits tight in the brackets.

Here it is.
I'm in the process of rebuilding my A/C so I have pic's of this kind of stuff.

shuttermutt · 11-04-2003, 08:19 AM

Quote:

Originally posted by Blue Beard
I have a new one in the box sitting in the garage.....

Very easy to come by..........

And it is how thick? 2 inches or 2-1/2 inches?

BobbyK · 11-04-2003, 11:53 AM

I can't measure mine cause it's back in the Blazer now but I did measure a spare pair of brackets.
The same type of brackets as in my posted pic.

They measure 2" exactly.You can see the actual core is wider than that.I'd say the core could easily be 2.5"

shuttermutt · 11-04-2003, 12:02 PM

See, when I tried the "new" cores from two different stores (the 2-inch thick ones), my clips wouldn't come close to cinching the core down. I had a good 3/8 or more of slack. That's why I had to re-core my original. Well, I didn't have to, but I chose to.

I'm not saying the 2-inch cores are all wrong. Never did. The books say they're right and many (most?) folks don't have a problem. Others have had the same problem I've had, though and that leads me to believe (as some have suggested) that there was either A) a factory option that got you the bigger core or B) a dealer option for cold climates that got the bigger core.

Of course, it could've been a short-run deal at the plant or the phase of the moon or... well, you get the idea. I was just curious if anyone had a definitive answer. Bah, I guess those that have the thinner core just get to save $50 when it comes time to replace it!

PanelDeland · 11-04-2003, 02:55 PM

Here's another theory for you.Maybe the thicker cores are for 'Burbs, blazers and panels.Since they have more interior they would benefit from the added core area.I have no way of knowing but maybe even the factory didn't realize the diff and just used them in everything.Or maybe it was because the outer boxes looked the same and were the same size.

shuttermutt · 11-04-2003, 03:17 PM

Hmmm... now there's a theory. Makes sense, too since those bigger passenger compartments would need a little extra heat.

BtnkBndt · 12-07-2003, 08:35 PM

I just spent a while at the parts stores looking for the correct core for my 67. My is the 2 1/2" thick one as mentioned above. I snatched the book at NAPA and looked myself. They offered 60-66 and 69-72 cores. Skipped 67-68? All the cores were 2" thick.

I just got back from a visit with Primered_69 (nice guy by the way). He had a busted heater box from a 69 with the core still inside. The core was 2". He let me take it and the brackets are perfect on my 67. Same but 1/2" shorter.

This one is on a heater only setup (no a/c). Heres a few pics if anyone is interested:

Brackets: left-67....right-69

BtnkBndt · 12-07-2003, 08:37 PM

Cores: Top-67....Bottom-69

Baradium · 12-07-2003, 09:26 PM

Oh great....

I busted the heater core on the '70 a month or so ago. So now I can know that whenever I go to replace it that I might have problems... great. I was going to go ahead and get it and try to put it in whenever I had a chance, this means I'll have to wait until I can schedule a time to try so I'll know if it doesn't work.

Any advice?

How hard is it to change out the cores? What all does it involve? I broke one of the hose nipples off on mine, which is why I need a new one.

BtnkBndt · 12-07-2003, 10:40 PM

It's pretty simple excepting the two bolts you can't see underneath and behind the fender. If you take all of the bolts from the fenderwell except the three up front you can drop the back of the fenderwell down about two inches. This way you can get the bolt behind the fender from the outside with a swivel an extension.

I was thinking the thick core might just bbe a 67-68 thing?

11-03-2003, 09:03 AM	#1
shuttermutt Don't say "Oops!", Doctor Join Date: Nov 2003 Location: Houston, TX Posts: 677	Unusually thick heater core A couple of weeks ago the heater core in my 68 CST (327/TH400/Air) sprung a leak. Actually, it was plugged solid. When I ordered a "new" one, it was 1/2-inch too thin. I ordered another one from a different supplier. It was 1/2-inch too thin as well. Finally, I took it to my trusty radiator guy. He looked it up in his magic book and it showed that, essentially, my core was 1/2-inch thicker than it should be. It's a Harrison unit, I'm 90% sure it's original, the factory clips that hold it in the black box fit it perfectly. What the heck is going on? I had my guy put a new core in between my tanks and I'm off and running again, but this is nagging at me. Why would mine be thicker than usual? __________________ 'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list

11-03-2003, 09:09 AM	#2
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,831	Sounds like you have the wider radiator....which isn't uncommon. There were two different sizes in the trucks...... The thicker one is probably just added another row........... __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo

11-03-2003, 10:40 AM	#3
ckhd Registered User Join Date: Oct 2000 Location: St. Johns, Arizona Posts: 2,660	It's the heater core not the radiator. Someone else had the exact same problem a year ago or so, can't remember who. They couldn't find a core thick enough. __________________ my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans?

11-03-2003, 10:51 AM	#4
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	shuttermutt Maybe it is a heavy duty heater option. Check the options on the glove box. I am not even sure if this was an option though. It may have been a dealer request for exteme climates like Maine. Just guessing I am not really sure. __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

11-03-2003, 11:21 AM	#5
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,052	I had the same problem on my '72 Blazer, every core I bought was too thin and left and air gap around the edge. I finally bought a good used one and has been in there ever since, as of now no supplier makes the correct replacment heater core. __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

11-03-2003, 11:34 AM	#6
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Yep, same thing here. I ended up with a bunch of polyethylene foam around mine to hold it in there. I don't know why the repro ones are smaller. Everything else is nearly the same, i.e., pipe sizes, lengths, and bends. I kept my old one in the box in case I ever want to have it fixed. It was in great shape except for a small pin hole. I don't think yours is 1/2" bigger, I think someone at Harrison (or wherever) got a wrong dimension and it's been wrong for several decades... __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

11-03-2003, 11:36 AM	#7
shuttermutt Don't say "Oops!", Doctor Join Date: Nov 2003 Location: Houston, TX Posts: 677	Mine wasn't so much that it left any kind of gap, but the clips that hold the core in place wouldn't tighten down. Instead, it just let the core flop around. The width and length were right, but the height (thickness) of the core was 1/2-inch off. I've checked two different books and they both listed the core at 2-inches thick. Mine is 2-1/2 inches thick. I don't doubt that the quality of the "new" heater cores isn't very good (I had a Four Seasons that looked like it had been soldered in a washing machine it was so banged up and ugly), but they're the same thickness as what's called for in every book I've checked. Hutch is probably right. There's nothing on the glove box sticker to indicate a special heater, but they may have just come that way for climates such as Northern Maine (where the truck was originally purchased). Either way, I'm thankful to have that extra thickness. Every little bit counts up here! __________________ 'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list

11-03-2003, 12:16 PM	#8
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	thats odd i thought they were all the same regardless i guess im lucky my new core fit great after i replaced the one that had almost 2 pounds of sludge in it compared to the new one. yes i weighed it __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

11-03-2003, 04:41 PM	#9
oldcarbuff Registered User Join Date: Sep 2002 Location: Muncie, IN U.S.A. Posts: 60	my truck has listed as an option "deluxe air heat". the code is 4342aa (I think--its a little faded). I only have three options all together, so I suspect this may be a heavier duty heater, as the cheap sonofagun who bought my truck new only got a rear bumper and overload springs for his other two options OCB

11-03-2003, 05:05 PM	#10
70 longbed Senior Member Join Date: Oct 2002 Location: Sierra Vista, AZ Posts: 489	shuttermutt, I had the same problem. I am sure that my core was original, and I could only find the thinner ones for replacement. I took mine to a radiator repair shop, and had it redone. It was a Harrison also. __________________ Keith 70 CST longbed in progress. Hoping to get it back on the road soon.

11-03-2003, 11:14 PM	#11
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,831	I have a new one in the box sitting in the garage..... Very easy to come by.......... __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo

11-04-2003, 03:05 AM	#12
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,772	I replaced mine with your run-of-the-mill replacement. It fits tight in the brackets. Here it is. I'm in the process of rebuilding my A/C so I have pic's of this kind of stuff. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

11-04-2003, 11:53 AM	#14
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,772	I can't measure mine cause it's back in the Blazer now but I did measure a spare pair of brackets. The same type of brackets as in my posted pic. They measure 2" exactly.You can see the actual core is wider than that.I'd say the core could easily be 2.5" __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

11-04-2003, 12:02 PM	#15
shuttermutt Don't say "Oops!", Doctor Join Date: Nov 2003 Location: Houston, TX Posts: 677	See, when I tried the "new" cores from two different stores (the 2-inch thick ones), my clips wouldn't come close to cinching the core down. I had a good 3/8 or more of slack. That's why I had to re-core my original. Well, I didn't have to, but I chose to. I'm not saying the 2-inch cores are all wrong. Never did. The books say they're right and many (most?) folks don't have a problem. Others have had the same problem I've had, though and that leads me to believe (as some have suggested) that there was either A) a factory option that got you the bigger core or B) a dealer option for cold climates that got the bigger core. Of course, it could've been a short-run deal at the plant or the phase of the moon or... well, you get the idea. I was just curious if anyone had a definitive answer. Bah, I guess those that have the thinner core just get to save $50 when it comes time to replace it! __________________ 'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list

11-04-2003, 02:55 PM	#16
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	Here's another theory for you.Maybe the thicker cores are for 'Burbs, blazers and panels.Since they have more interior they would benefit from the added core area.I have no way of knowing but maybe even the factory didn't realize the diff and just used them in everything.Or maybe it was because the outer boxes looked the same and were the same size. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"



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11-04-2003, 03:17 PM	#17
shuttermutt Don't say "Oops!", Doctor Join Date: Nov 2003 Location: Houston, TX Posts: 677	Hmmm... now there's a theory. Makes sense, too since those bigger passenger compartments would need a little extra heat. __________________ 'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list

12-07-2003, 08:35 PM	#18
BtnkBndt Pennyless Fool Join Date: Oct 2003 Location: Forney,Tx Posts: 439	I just spent a while at the parts stores looking for the correct core for my 67. My is the 2 1/2" thick one as mentioned above. I snatched the book at NAPA and looked myself. They offered 60-66 and 69-72 cores. Skipped 67-68? All the cores were 2" thick. I just got back from a visit with Primered_69 (nice guy by the way). He had a busted heater box from a 69 with the core still inside. The core was 2". He let me take it and the brackets are perfect on my 67. Same but 1/2" shorter. This one is on a heater only setup (no a/c). Heres a few pics if anyone is interested: Brackets: left-67....right-69 Attached Images __________________ "Who owns this car with the peace sign, the mag wheels, and four on the floor?" 67 Short Step 283/TH400/4.11 Last edited by BtnkBndt; 12-07-2003 at 08:41 PM.

12-07-2003, 08:37 PM	#19
BtnkBndt Pennyless Fool Join Date: Oct 2003 Location: Forney,Tx Posts: 439	Cores: Top-67....Bottom-69 Attached Images __________________ "Who owns this car with the peace sign, the mag wheels, and four on the floor?" 67 Short Step 283/TH400/4.11

12-07-2003, 09:26 PM	#20
Baradium Binder Rep Join Date: Jan 2001 Location: Salcha, AK Posts: 1,506	Oh great.... I busted the heater core on the '70 a month or so ago. So now I can know that whenever I go to replace it that I might have problems... great. I was going to go ahead and get it and try to put it in whenever I had a chance, this means I'll have to wait until I can schedule a time to try so I'll know if it doesn't work. Any advice? How hard is it to change out the cores? What all does it involve? I broke one of the hose nipples off on mine, which is why I need a new one.

12-07-2003, 10:40 PM	#21
BtnkBndt Pennyless Fool Join Date: Oct 2003 Location: Forney,Tx Posts: 439	It's pretty simple excepting the two bolts you can't see underneath and behind the fender. If you take all of the bolts from the fenderwell except the three up front you can drop the back of the fenderwell down about two inches. This way you can get the bolt behind the fender from the outside with a swivel an extension. I was thinking the thick core might just bbe a 67-68 thing? __________________ "Who owns this car with the peace sign, the mag wheels, and four on the floor?" 67 Short Step 283/TH400/4.11

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