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About 3 years ago the heater in my shitbox silverado went out so I just bypassed the heater core and went on about my business. Luckily, I live in Mississippi and like most chests, mine looks better when my nips are hard anyway, so the chill didn't bother me, and when it was cold enough to so, I'd just rip in something else. Well, my 5yo daughter has come to love riding in the truck, so with that, I needed heat. Before taking the dreaded plunge into a weekend full of dash pulling, I decided to try something on a Hail Mary, AND IT WORKED!!
I started by covering my engine in an old tarp (cold engine, of course) then took a water hose and tried running water through the inlet to the heater core but it was completely stopped-up. Then tried running water backwards through the outlet and was able to get a little bit of awful, rusty brown water to come out the other side. I continued going back and forth from inlet to outlet until I was able to get a little water to come out of both sides.
I then threw a floor jack under the front of the truck and like sex with my wife, I gave it a couple of pumps and was content. I then took a bottle of what's called EVAPO-RUST (found it at my local hardware store a year or so back) and after fabricating a funnel with a fuel hose end, I filled both the inlet and outlet hoses to the heater core with it, and went inside and went to bed. Woke up this morning, let the jack down and went at the hose inlet and outlet again with the water hose and I couldn't believe how much crud came out and after about 10min of back and forth, it was clean water passing through and was flowing like a river. I reattached my previously bypassed hoses back up and went for a drive. It 100% fixed my heater issue! No dash pulling, no headaches, just a water hose and a $10 bottle of rust remover!
I know it's a long read, but it's getting to be cold weather season for a lot of people, and hopefully this helps someone else stay warm this winter for a lot less time and money than I was afraid I was about to invest. Hope it works for someone else!
Glad that this solved your blockage! Unfortunately, many heater core failures manifest as a leak rather than a blockage, so then stuff has to come apart to fix it. But for a simple blockage, looks like you found a worthwhile product.
Glad that this solved your blockage! Unfortunately, many heater core failures manifest as a leak rather than a blockage, so then stuff has to come apart to fix it. But for a simple blockage, looks like you found a worthwhile product.
You're 100% right. For a wet passenger floorboard, unfortunately the only fix is going to be the dreaded core change which I haven't found a viable shortcut for. Hopefully someone else here has a blockage issue like I did and comes across this before wasting the time and/or money changing out the core. My blockage is just more proof as to why you should use distilled water in your cooling system vs. tap water. Mineral deposits from tap water are a very real thing inside of an engine!
10-28-2022, 01:58 AM
$10 HEATER CORE FIX! (seriously, no BS) 
But for a simple blockage, looks like you found a worthwhile product.