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Unclog a heater core...

jonrpick

jonrpick

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Good lord, it's been forever since I logged on! Life and all...

My brothers, I desperately need to get heat in my 2005 Blazer (S-10). The core is clogged. The shop that recently performed some work for me said it was like 10hrs of labor according to book value to replace the core. The inlet hose is hot, the outlet is cold. Clogged core. So, in an effort to save some money and keep from freezing I'm going to attempt to unclog it.

I've seen some online videos where compressed air was used, blowing in through the outlet port, like a reverse flush with air. I'm just wondering if anyone has any trade secrets that may help. Is there any type of chemical cleaner I can use that may help break down whatever has clogged it (CLR, etc..?). The shop manager suspected someone had used either the wrong coolant, or something other than distilled water.

I take my 2yr old son to day care each morning, and while I can handle the cold, I don't want to expose him to it. Any and all advice will be appreciated before I dive in.

Thanks!
 
i always just did the garden hose backflush on the outlet to blow the slug out the inlet .i also go back and forth a few times after it starts flowing . get a good mix of pressure / flow going to unlock that sludge .

but i think clr might do the truck .

and the s-10 stuff is notorious for plugged cores . mostly from the dex-cool sludge up problem.
 
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I'm reading up on the Dex Cool sludge issue. Is it a soft sludge or hard, like scaling that builds up?
 
Usually just water pressure from a garden hose is enough to reverse flush a heater core out well enough--high pressure ,either air or water,can make it leak,then your boned..

It may be it already had leaked,and someone put stop-leak in the radiator,it often ends up in the heater core and clohs it...the antifreeze usually clots like jello when it goes sour or gets mixed with incompatible coolants..

If it does end up leaking after it is flushed,you can use Aluma-Seal or Copper-Seal powdered stop leak,that is the only stuff that wont clog things up in my experience..the Bars-Leak "rabbit pellets" in that brown gooey liquid likes to clog heater cores..so does most liquid stop leaks..

"Porter-Seal" is the worst!..(if it is even sold any more)..it does stop leaks great,but clogs everything,its best used on home hot water boilers that cracked--I heard its just ground up feldspar,and was invented during WWII ,to use in military trucks that got shot up in combat conditions..

My friend had an old Volvo that had a junk heater core--that car must have had the heater core installed first,then the rest of the car built around it..it was a nightmare job to replace,so he decided to buy a heater core and build his own box to mount it in,and he hole sawed two holes for the heater hoses thru the firewall and used flexible duct hose to connect it to the defroster ducts--he used a GM blower motor & fan off a square body too..it ended up working better than the original heater,but didn't win any appearance awards...beat freezing though!..
 
"He's Back! Back in the New York Groove..."


And I'm no help here. My heater core currently makes the blazers passenger floor hot, green, and steamy.
 
Yeah just blow it out gently in the reverse direction with air and then a garden hose. I had a '99 Taurus for a bit that would plug every year with sediment and crap.
 
My friend has to flush many heater cores out at his shop this time of the year..he's about the only guy in town that will tackle replacing many heater cores that suck to replace too,so he's usually busy !..
Some vehicles the entire dash has to come out,and even the steering colum too,or at least dropped to get the dash out..whoever "engineers" this type of crap needs to be sentenced to replace a few him or herself!..
 
I’ve done the reverse flush with a water hose before and it worked fine. It lasted about 6 months before I had the same issues but 6 months was enough time to build up the nerve to dive into it. Lol
 
I've had plenty of issues with the heater core starting to leak after un-clogging it. Usually there is some chemical issue with the coolant to cause a blockage in the first place, and that blockage may be holding the coolant into the core.

That said, I'm a fan of the garden hose on the outlet side of the heater core and running it till it comes out clean.
 
jonrpick said:
Good lord, it's been forever since I logged on! Life and all...

My brothers, I desperately need to get heat in my 2005 Blazer (S-10). The core is clogged. The shop that recently performed some work for me said it was like 10hrs of labor according to book value to replace the core. The inlet hose is hot, the outlet is cold. Clogged core. So, in an effort to save some money and keep from freezing I'm going to attempt to unclog it.

I've seen some online videos where compressed air was used, blowing in through the outlet port, like a reverse flush with air. I'm just wondering if anyone has any trade secrets that may help. Is there any type of chemical cleaner I can use that may help break down whatever has clogged it (CLR, etc..?). The shop manager suspected someone had used either the wrong coolant, or something other than distilled water.

I take my 2yr old son to day care each morning, and while I can handle the cold, I don't want to expose him to it. Any and all advice will be appreciated before I dive in.

Thanks!
Click to expand...
Late to this party but I concur w back flushing w a hose.
Try a cup of iron out mixed w distilled water to dissolve hard water and rust in the system. Run it up to full temp then drain and refill w 50/50
Good luck
 
It's probably not a dex-cool sludge issue. 4.3's were notorious for casting sand being left in the cooling jackets of the block and when dislodged it circulates and gets into the heater core and clogs.

Backflushing is about the only way to clear it short of actually replacing the core itself. The tool you need is like this:
IMG_7617.jpg


Hook that up to your garden hose, add the shop air and give it a couple of quick blasts. DON'T lay on the compressed air for any more than a quick burst unless you really want to change your heater core. You'll end up with a few gallons on the floor of the Blazer pretty quickly.

We had a customer's S10 Blazer come in wanting a coolant flush and we did as asked. Only after that to find that the heater core clogged up. We tried multiple ways and couldn't get the clog to clear. Then my tech pulled out the blaster. He might have hit the air 3 times and we got the flow back. One thing we noticed was the water that came out and covered the floor was covered in fine sand. He let the water run by itself for a few minutes after the clog cleared just to make sure it all came out.
 
Hark! I hear the sound of a distant drum.....

I'd tend to stick with the garden hose. And not too much pressure if it does not flow quickly. Those cores are made of very thin material, and probably already has some corrosion. Splitting the core is usually considered a bad thing.
If it does leak afterward, and they sometimes do just from corrosion that got cleaned out rather than pressure, I suggest a after market replacement to keep the little nipper warm rather than a possibly multi-day replacement job.
That would keep things going until summer.
I hear nothing but good things about these:
https://www.flex-a-lite.com/mojave-heater-179.html
You may want the installation kit with the cut off valve.
This gives you an indication of the price.
https://www.amazon.com/Flex-a-lite-640-Mojave-Heater/dp/B000CNJBPU
You may also want the defrost kit that you can buy.
There are several folk online here who have used these, I'm sure they will chime in with suggestions.
 
Update: the reverse flow operation did exactly.... nothing. No movement, not even air.

I have a 2:1 mix of lye drain cleaner:water in a vertical hose directed down into the inlet of the core. Now we wait...
 
There isn't a cutoff valve in the system behind the firewall is there?
Its unusual for nothing to go through. All the older trucks used to have one, but most don't these days. You might have a vacuum line off if its a vacuum valve.
 
Doing the core in those isn't that bad. Book calls for about 10hr, but it can be done in 2 or so. Basically you pull the center counsel, drop the column then remove some brackets/supports along the windshield and the entire dash just flops down, hinging off some bolts in the A-pillars.
 
Jay... I think all the post 1995 S-10 style trucks just used an electric flapper to divert air over the core.

I know when the temp control is changed from cold to hot, the difference in air speed as well as the way it sounds, changes noticeably, which tells me the air is in fact being diverted.

@toomany yes... I saw a guy on YouTube do a "heater core in an hour" video.
 
Yep, that is what I thought too, but its just so unusual for no water to come through at all I just wondered.
 
Haven't attempted another flush yet. The lye initially hissed, then stopped. 30mins later the hissing sound returned. That tells me it's doing something. Hopefully something good.
 
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