The times I have done a coolant flush, was to follow directions with the flush liquid. Then back flush the heater core with a garden hose. Good to go after that.

 

What we usually do at work, back-flush, forward-flush, then back-flush the heater core, with a garden hose (we have a nozzle made specifically for this, but any will work) take whatever flushing solution your heart desires, usually comes in a smaller bottle, half liter or so, put a small piece of heater hose onto the heater core (both inlet and outlet disconnected on it, and just one piece of hose on it, a foot long or so) then dump some of that flushing solution into it. Let it sit for 10 or 15 minutes, then back-flush again. You'd be surprised at how much you get out by doing that.

If it's really plugged, we'll use muriatic acid. You just have to be careful with the stuff. Don't touch it, breathe it, or look at it. Don't let it sit on the concrete unless you wanna see what it looks like inside. Dump a good amount of that in there, let it sit for 10 or 15 seconds (No more. Bad things will happen.) then flush it immediately. Would not recommend this route if you've never used the stuff before. You will destroy the heater core.

 

Safe chemical to use is actually automatic dishwashing soap.

 

CLR or ice machine cleaner (phosphoric acid) might be a safer alternative to muriatic as well.

 

I use acetic acid... far milder...

 

I would never use acetic acid. I usually use Vinegar

 

What year is this thing? I think his question is more specifically where is he going to disconnect....if you disconnect any GM style quick connects, you'll want to replace the quick connect as well because they usually leak after.

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Welcome to the forums!

 

It's a 94 K1500. Yes - my question is about where to disconnect the hoses. I'm used to seeing two rubber hoses, not the "weird" one that I've got coming off the thermostat housing...

 

I used to have a 90 K1500 Z71 and I thought my heater core went out as it started leaking badly all over the carpet - all this many years ago. Anyhow, I removed the heater core, replacing the carpet with rubber, and could not find a single leak in the core. So I replaced all the seals and reinstalled. Problem solved. Good luck!

 

Yeah its cheap too. I like Heinz. it cleans out my tubes.