CLR repair of completely blocked heater core/hose

Joined
May 21, 2012
Messages
6,762
Location
Fort Lauderdale, FL
2002 Chevrolet Blazer 4.3 V6


The story starts with my friend trying to use his heater, as temps in FL have dropped at night for the past month. No heat. I began an inspection of the cooling system's hoses fearing the worst. When I felt the heater hose that comes off of the intake manifold and goes to the heater core, I determined that either the hose was completely blocked with solid matter from manifold to heater core, or it was really happy to see me.

This is just a little of what came out:



The heater core was equally blocked with crud.

I started by replacing the blocked hose with a new hose. I connected it to the heater core and tried to blow through the core, and got nothing. I decided to try to backflush it. I cut off the end of an old garden hose I had, inserted a 5/8" double barb connector, and stuck the other end of the connector into the heater hose coming out of the core, connected the other end of the cut off garden hose to my actual garden hose, and carefully opened the water. The heater hose got real hard, but no water came out of the inlet heater hose.

The core was obviously in the same shape as the original hose. I didn't have a bucket-flush arrangement with me (not that it would have worked), so I started treating the core with CLR by holding the heater hose up high and pouring straight CLR right down into the hose. I saw the CLR start to fizz and sink down into the hose. I topped off the hose and secured the hose high up against the hood and waited. It went down some more, and I topped it off again and waited.

After about 15 min, I poured more CLR in and connected the garden hose and hose barb arrangement back to the heater hose to see if I got any different results. Magic! Water, CLR, and a ton of rust gunk started drizzling from the other hose. It didn't last, however, and the water stopped flowing completely. The core was completely blocked again.

I repeated the CLR application directly to the exit hose, and set up and waited again. I then repeated the garden hose treatment. This time, water came flowing out pretty good.

The next step was to drain as much water from the hose as possible, and then pour CLR down the inlet and outlet hoses. I used the garden hose again, but this time on the inlet hose, and got even more flow.

Now I filled both hoses with CLR, connected both hoses back to the engine before it could drain out, filled the radiator with a half gallon of CLR, and ran the engine. I still got no heat at first, but it steadily got warmer, until it was pretty hot. I kept massaging the hose coming out of the heater core toward the water pump to prevent any big chunks from clogging the hose. I wasn't worried about the big chunks finding their way into the rest of the system, because I knew they'd be chopped up by the water pump and dissolved by the CLR. I had already tested this theory with chunks that had fallen out of the original clogged hose that I removed.

It was now time for the final rinse/flush. I disconnected the heater hose returning to the water pump and set it aside so it could blow the water out onto the ground. This would both eliminate the thermostat as an impedance to water flowing out of the block, as well as guarantee that anything coming out of the heater core would end up on the ground, and out of the engine. I then connected garden hose arrangement to a spare heater hose and connected that heater hose to the water pump. I left everything else connected and closed, and removed the hose going to the overflow tank. The effect of this whole thing is that the heater core can be exposed to full safe pressure since the radiator cap would still continue to regulate pressure in the cooling system, and direct all of that pressure to the heater core, while simultaneously providing a complete flush of the entire cooling system.

Things were still going kind of bad at first. The radiator cap was bypassing a lot of water, and not a whole heck of a lot was coming out of the heater hose. But things steadily improved until there was full water flow coming out of the heater hose, and the radiator cap has stopped releasing pressure completely. I then opened the drain cock for the radiator, and a whole new flow of garbage came pouring out. I left the drain cock out, so the lower radiator could continue dumping the rusty trash and CLR mix out of there. I left this going for about a half an hour.

When that was done, I removed my setup, reconnected everything, and dumped diluted baking soda in the system to deactivate any of the acid that might still remain in the system. Then I did my garden hose flush of the engine again, drained everything from radiator and block, and filled the system with distilled/Dexcool.

The amount of rusty garbage that came out of the system was unbelievable. There's neglect, and then there was this. When all was said and done, the engine ran about 10 degrees cooler and the heat was blasting fire. His wife and kids had ought to be happy on those cool nights.
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Just a little of the rust trash covering the ground after coming out:



Heater hose/garden hose connected to water pump inlet, and disconnected heater core outlet hose dumping rusty trash at full flow onto the ground:



Full flow, and running clear:



Garden hose/garden hose/heater hose contraption:



If it sounds long and complex, well it was. But it was also successful, so I'm not complaining, and neither is my friend.
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Originally Posted By: DoubleWasp
I didn't think for one second that it was going to be successful, until it was.
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this is exactly what I thought as I was reading on, and then it worked!

your a good story teller, so it wasn't boring to read it thoroughly.
 
CLR does wonders for cleaning up nasty scale and build up in pipes and toilet tanks and other things like that. Full strength right from the bottle always does the trick. I always wondered about how it would work on a clogged heater core and now I have proof!
 
Great persistence buddy -- im sure your friend & his family are thrilled. Nice steak dinner for you would be a nice reward from them!!
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Glad to see great results. I used the Zep version of CLR to clean a neglected cooling system on a 1984 K30 that I used to own. Added to the cooling system and drove around for a while. I couldn't believe the [censored] that came out of there.
 
Originally Posted By: Gasbuggy
SteveSRT8 is probably forwarding this thread to the EPA as we speak
He is not from California.
 
Originally Posted By: andyd
Good job with the fix. What I want to know is what created the scale? Running pure tap water?


That's exactly what I want to know. What got it that bad in the first place? All that corrosion has to be a product of something internal, even very hard tap water doesn't have enough carbonates to clog a heater core unless you have a massive leak and have been topping it off for years.

But good job on cleaning it, hopefully it doesn't end up that way again.
 
Originally Posted By: kschachn
Originally Posted By: andyd
Good job with the fix. What I want to know is what created the scale? Running pure tap water?


That's exactly what I want to know. What got it that bad in the first place? All that corrosion has to be a product of something internal, even very hard tap water doesn't have enough carbonates to clog a heater core unless you have a massive leak and have been topping it off for years.

But good job on cleaning it, hopefully it doesn't end up that way again.

This is a known issue with that engine. The radiator caps were bad from the factory and let too much coolant escape. Pretty soon the level is low enough that iron parts of the engine are exposed to air, and it starts rusting internally. The rust particulate gums up the radiator cap and the problem grows worse.
Most people don't check their coolant level, or at best, a quick lube will check the overflow only since the engine is too hot to open the radiator cap.
So these 4.3Ls will drive around for years with coolant a gallon or more low.
 
Originally Posted By: Colt45ws
Originally Posted By: kschachn
Originally Posted By: andyd
Good job with the fix. What I want to know is what created the scale? Running pure tap water?


That's exactly what I want to know. What got it that bad in the first place? All that corrosion has to be a product of something internal, even very hard tap water doesn't have enough carbonates to clog a heater core unless you have a massive leak and have been topping it off for years.

But good job on cleaning it, hopefully it doesn't end up that way again.

This is a known issue with that engine.


I gotta agree. Several years ago, I replaced a defective thermostat on a similar vehicle, except it was a pickup. Once the vehicle warmed up, I noticed there was no heat in the cab. I had to back flush the heater core because it was completely plugged. All kinds of junk came out of that one. The guy was amazed that a defective thermostat could make such a difference in cab heat, LOL!
 
Hello, Great tale.

I had the same experience.
Substitute the car to sister's 1988 4.0L Jeep XJ.
Substitute the phrase, "...no heat but the heater hose TO the core SLOWLY grew a bit warmer..." and
"I concluded the core was plugged".

Years of radiator STOP-LEAK products plugged the core with a grey putty. The core is the system's lowest point.

Every household product was useless. I HAD to resort to gasoline to dissolve the goo.

The back of the radiator had stalagmites in 7 different colors. They all held so I didn't have to EVER change the radiator.

Hot air blew. I felt like a star. Sis was overjoyed. Kira
 
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