Really... heater core.

[Skylark]

So I recently flushed the cooling system and today the heater core blew. It figures, I NEED the truck tomorrow and Saturday. I have to pull a travel trailer for my dad and the Civic isn't going to cut it! We have an issue with the defroster anyway so it looks like I will be pulling the heater box and going through the whole thing. To get me through the weekend I will buy a nipple and about 3' of hose to bypass from the thermostat directly to the radiator. Oh well.

 

[3500GMC]

Yep, for now just take the heater core out of the loop.

Sucks for you, though.. I 'hear' these are un-fun.

 

[handcannon]

Do you need to pull the dash to access the heater core?

Don

 

[someotherguy]

Skylark...once you're ready to dive in, you can do the heater core with zero dash removal; the lower cover on the heat/AC box comes off with a little bit of work. It's one of those things that I always say on some of our trucks it's a simple job, other ones it SHOULD be simple but is a huge pain in the ass. There's like 6 screws on it, and 1 is hidden between the case and firewall, another one is hidden a little bit sunken into the plastic along the lower ridge of the evaporator core. No big deal. A 1/4" ratchet with a couple extensions will get you up to the one hidden by the firewall.

Here's the locations of the cover screws, circled:

Note that the new core may come with a new retainer clip since some of them don't have the exact same tank size as the original. When you replace the lower cover take your time to carefully line it back up as you'll see it has a lip all the way around it that can be a little tricky to get exactly right, especially with the carpet against the firewall fighting you. I see a lot of these cracked at the corner from people forcing them.

What kind of problems are you having with the defrost? Most common issue is the linkages on the vent position actuator get gummed up. Yep, it's got linkages, it's the only one out of the three that has them. Just above the driver's side of the transmission hump:

Note that the flat metal parts are two-piece sliders; they're lubed at the factory and eventually gum up and quit working or work very slowly. Lay down some newspaper to protect the floor and spray the linkages with WD40, then run the vent position controls back and forth slowly through all the settings to "work" the linkages and unstick them. Then wipe off the excess and apply a little white lithium grease.

Richard

 

[bison]

Now that is show and tell at its finest.
Good job someotherguy,...looks to me that top pic was taken with the whole box out of the truck,...am i right?

I could not get to that high up screw at the firewall(carpet was in the way)i ended up cutting the cover trough along the firewall.

 

[someotherguy]

Yep - that was a series of pics I took of disassembling the box to get to the evaporator core (and to show how disgustingly covered in crud they get.) There's no way to take the box apart past the heater core unless it's out of the truck, but getting to the heater core itself is totally do-able without messing with the dash at all. Can't get a clear picture of the screw positions though while it's in the truck.

The trick is definitely in extensions, and it doesn't hurt to tape each joint together with masking tape if the fit is particularly tight.

It's really not necessary but you could also get a little access/play in the box if you loosen or remove all the bolts that hold the box to the firewall but it's a lot of extra work that shouldn't need to be done. If one chooses to do so, remember that all of the bolts EXCEPT ONE are accessed through the engine compartment side of the firewall and one is hidden behind the coolant bottle, the final bolt that will escape you is accessed from the interior side of the firewall and is at the top of the evaporator core. You can get the idea of its location because you can see the end of it in the engine compartment side poking out just above the top evaporator line. To get to it you use a 10mm socket and a long extension and run it across the driver's side of the evaporator core hump in the ductwork box just past the blower motor resistor. It's kind of a long bolt. Oh, and remember when putting them all back in that all those other bolts go directly into plastic so be sure to thread them straight, and don't overtighten.

Richard

 

[Skylark]

Richard, posts like above are why i was disappointed when you weren't around FSC. Here is where a good thing comes around though. I have to go to Portland, OR for training on Sunday. We decided to take the truck because we are going to do some camping along the Columbia River. A buddy of mine lives up there and we were to visit while in the area. When he heard about the heater core and knowing about the HVAC problems that we are having, he offered to take the truck to work and fix it! He knows about my wife's health issues and knows that she needs to be temperature controlled. I had forgot that I'd helped him out with acquiring some much needed medical equipment for his wife about a year ago so he said that he would cover all of the parts and do all of the labor. He and I went to college together in the 90's for auto tech and I went another direction while he apprenticed for a local Chevy dealer. He is still a mechanic while I work in a cleaner field... So the lesson here, do unto others as you would have done to you. It works!

 

[ak diesel driver]

karma

 

[someotherguy]

Here is where a good thing comes around though. I have to go to Portland, OR for training on Sunday. We decided to take the truck because we are going to do some camping along the Columbia River. A buddy of mine lives up there and we were to visit while in the area. When he heard about the heater core and knowing about the HVAC problems that we are having, he offered to take the truck to work and fix it! He knows about my wife's health issues and knows that she needs to be temperature controlled. I had forgot that I'd helped him out with acquiring some much needed medical equipment for his wife about a year ago so he said that he would cover all of the parts and do all of the labor. He and I went to college together in the 90's for auto tech and I went another direction while he apprenticed for a local Chevy dealer. He is still a mechanic while I work in a cleaner field... So the lesson here, do unto others as you would have done to you. It works!

Awesome! Sounds like it worked out great; a good friend to have.

Richard, posts like above are why i was disappointed when you weren't around FSC.

I've been on Chevytalk longer than FSC and have found that the discussion and membership in general is a lot more well-behaved on Chevytalk. Not pretending I'm some saint, I can easily be an ass if someone steps on my toes, but I'm really on the forums for the purpose of helping others and learning from others. FSC doesn't seem to foster that mentality very well, which is a shame because they do have a few great members...that are often overshadowed by a bunch of clowns. With that said, and not to take anything away from Truckstop, you might check out Chevytalk too. It's a pretty active site and the sections are divided up to cover pretty much all Chevy models, not just trucks; the 88-98 fullsize truck forum is one of the busiest on the site.

Richard

 

[bison]

Well,TTS is as close to GM diesel paradise as it gets,and diesels is what matters eh.

 

[restoguy]

So I recently flushed the cooling system and today the heater core blew...

Maybe not as coincedental as you think. When the water pump went bad on my '94 I put some stop leak in because I had to drive it 3 more days before I could fix it. (didn't really help much though) So I FLUSHED the system when I did the pump to get the gunk out. Less than a week later...HEATER CORE. I did it laying in a puddle of fresh antifreeze on the pass floor board in a hotel parking lot. It was awesome... I'm no Dick Tracy, but I believe I see a pattern here!