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Heater core replacement

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bigmike72

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Just thought I'd share my experience with a heater core replacement on a first gen. First there is a great article about this for '75-'91 blazers in the technical section which I used and I only have a few things to note:
-The heater core was $25 at pep boys. About 10 years ago, I had a heater core replaced on a 80 blazer at a shop...this cost me $200 which would probably be more today. Which leads me to the next point...
-It's really only about a 2 hour job on a first gen and is extremely easy even without power tools. Biggest hang-up for me is that it looked like I could get all of the bolts/nuts without moving the fender. After contorting myself to get what looked like the last bolt, I tried to remove the heater core/blower housing. There is definitely one more bolt (on the firewall and close to the right fender) and you do pretty much need to move the fender or cut a hole in it to get at it. I moved the fender by pulling enough bolts to allow it to bend and give me access to the bolt.
-Note that on a first gen, the heater core is in the engine compartment and on later models it is on the car interior side of the firewall.
-Make sure you remove the heater flap cable before pulling the core's housing. You can get at the cable from inside the truck, in the passenger footwell you'll see a cable running through a rubber cover in the heater ducting. Remove this cover and pull the end of the cable off of the heater flap.
-The core housing is removed and the core is attached directly to it with some screws that go into metals straps around the core (you won't see the straps until you pull the housing). Leave these screws attached until you pull the housing.
-On a first gen (at least on my 72) the bottom heater line is 3/4" hose and the top line is 5/8" (or maybe it's just wrong in the tech section).

After looking under my dash today, I found my next project. There is no ducting running up to the top side of the dash. The main duct is made of metal and it looks like these upper heat/defrost ducts must have been plastic or similar. I'll be taking some measurements and off to home depot to see what I can scare up. Looks like maybe a 10 minute job /forums/images/graemlins/smile.gif
 
hey, were in So Cal are you...I need to move one of my fenders back and the other one forward... /forums/images/graemlins/thumb.gif
 
I'm in Westminster near Edinger and Newland. Basically right across the 405 from the HB mall or whatever it is called these days.

BTW, you move the inner fender to get at heater core but I'm more than willing to help move your fenders if you want to help with mine /forums/images/graemlins/smile.gif Where are you located?
 
Cool thanks for the tip about going to pep boys... thats about half the cost of what i payed last time....
I leaned on the heater core when i had to change the heads on my engine... Heater core started leaking a bunch.. Well now its getting cold and its time to replace that heater core. /forums/images/graemlins/thumb.gif /forums/images/graemlins/pimp1.gif
 
dude, your right in my back yard...I'm in Fountain Valley...by mile square park.
have you seen my yellow first gen driving around?
 
Damn, that's close...you're basically right down the street from me about a mile or so to mile square park from here. My folks actually live in FV and we just moved from there as well but down off of Magnolia and Ellis. Sorry haven't seen your truck driving around, have you seen mine? It's orange with a white top 17" welds and BFG AT's (Probably not since I've only had it a month and it's not a DD.)
Anyway, I'd love to come check out the truck sometime. It sounds like something that could inspire some more work on mine /forums/images/graemlins/smile.gif
 
hey, my wife has a friend right around the corner from you. She told me about seeing an orange K5 every time she went over there, so tonight after dinner she took me over to see the k5...nice truck...I'm about 1/8 of a mile from you...
 
bigmike72 said:
Just thought I'd share my experience with a heater core replacement on a first gen. First there is a great article about this for '75-'91 blazers in the technical section which I used and I only have a few things to note:
-The heater core was $25 at pep boys. About 10 years ago, I had a heater core replaced on a 80 blazer at a shop...this cost me $200 which would probably be more today. Which leads me to the next point...
-It's really only about a 2 hour job on a first gen and is extremely easy even without power tools. Biggest hang-up for me is that it looked like I could get all of the bolts/nuts without moving the fender. After contorting myself to get what looked like the last bolt, I tried to remove the heater core/blower housing. There is definitely one more bolt (on the firewall and close to the right fender) and you do pretty much need to move the fender or cut a hole in it to get at it. I moved the fender by pulling enough bolts to allow it to bend and give me access to the bolt.
-Note that on a first gen, the heater core is in the engine compartment and on later models it is on the car interior side of the firewall.
-Make sure you remove the heater flap cable before pulling the core's housing. You can get at the cable from inside the truck, in the passenger footwell you'll see a cable running through a rubber cover in the heater ducting. Remove this cover and pull the end of the cable off of the heater flap.
-The core housing is removed and the core is attached directly to it with some screws that go into metals straps around the core (you won't see the straps until you pull the housing). Leave these screws attached until you pull the housing.
-On a first gen (at least on my 72) the bottom heater line is 3/4" hose and the top line is 5/8" (or maybe it's just wrong in the tech section).

After looking under my dash today, I found my next project. There is no ducting running up to the top side of the dash. The main duct is made of metal and it looks like these upper heat/defrost ducts must have been plastic or similar. I'll be taking some measurements and off to home depot to see what I can scare up. Looks like maybe a 10 minute job /forums/images/graemlins/smile.gif
Click to expand...


My heater core is in the cab and it's a '70?
 
Hi guys. Just a quick question, since I already have replaced my heater core, then realized I had put the two fastening brackets on wrong and had to take it all out again and put it all back in again. This post starts off saying that its 3/4 on the bottom and 5/8 on the top, but mine is the reverse because all the literature I could find said 3/4 goes on top and 5/8 on the bottom. Does anyone know if it matters? Is all that matters where the hoses connect? (i.e. 3/4 goes to water pump and 5/8 goes to intake manifold)?
Just curious for the NEXT time I have to replace the core. :wink1:
 
It may depend on whether you have AC or not. The heater cores are different. The service manual has a diagram on which hoses go where.
 
Hi Brian. I got the impression from his post that his was in the engine compartment, like mine, without AC. It may not (probably doesnt) make a difference., but I was just thinking that they had set it up in the same manner as the auto trans cooler, where you want it going in on the bottom and out on the top, so that it doesnt just waterfall through. So then it would just depend on where the hoses were connected.
 
You might be right. As far as the hoses being on top or bottom, I don't think you can switch them around can you?

In any case, on mine the smaller lower hose comes from the water pump and the larger hose goes to the radiator. This sounds the same as you are describing.
 
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