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heatercore clogged how to

10-06-2004, 04:14 PM
91 s10 4.3 blowing cold air inlet hose is hot outlet hose is cold
figured its clogged is there a product i could use to unclog it,
could i use a waterhose a flush it out in reverse??? dont really want to have to get a new on if i can salvage this one.

10-06-2004, 07:49 PM
Already a thread on here about that.Scroll down.

10-06-2004, 08:53 PM
Yes, you can reverse flush it but IMHO, replace it. When the frost is on the pumpkin, you'll be glad you did.

10-06-2004, 10:22 PM
thanks ill replace it if not able to unclog it

10-06-2004, 11:46 PM
Only replace a heater core if it leaks, never replace it for being clogged.

This is not a 30 minute job and replacement should be a last ditch effort.

Go to your dealer or a good equipped shop and have them triple acid reverse flush it and it should take it out for you.

You need professionals with the right chemicals to do it right.

Trust me, it will be cheaper in the long run.

BTW, you sure it is plugged, have you felt both heater core lines to make sure one is warm and one is cold?

10-07-2004, 09:04 AM
Check your heater control valve on the collant lines going to the heater core. If working right 1 line going into the heater core should be hot and the sec should be WARM not cold.
I the line comming out of the heater core is cold then its pluged.
Replace it dont use any heavy chemicals because you will NEVER get all that junk out of the coolant system and the chemicals could cause you move problems like water pump and head gasket problems
Retired GM Master Tech
Ase Master Tech

10-07-2004, 02:54 PM
A good triple reverse flush will get most of it out and that is the point.

I know, I had to have mine done three years ago when I unknowing mixed the green with the orange and sludged up the heater core completely.

They unplugged it and I haven't had anything coming out other than small amounts when I first started driving it when it was just flushed.

Most of the sludge went into the coolant recover tank where I sucked it out and all was good.

They wanted me to replace the core but I insisted they try the flush first. No offense intended, but mechanics like to replace parts rather than trying to fix them as they are. The one thing you have to see is that a heater core replacement is a bigtime job for a shadetree mechanic that has never done it before and it should be a last ditch effort and only considered the first thing to do if it is leaking.

10-07-2004, 11:55 PM
took blazerlts advice and flushed it nice hot air was the result thanks all.

10-08-2004, 12:11 AM
Can I get a WOOP WOOP!

WOOHOO! I love when my help works.


10-08-2004, 12:31 AM
When you live in the middle of no-where like I do you learn to improvise.. Liquid draino will also clear cloged rads, and heater cores. just fill them, let them sit 1/2 hour or so, flush with water, and I blow them out with compressed air. (CLR also works)

10-14-2004, 05:38 PM
My 96 S10 4.3 is doing the same thing. I am pretty good with tools but have been away from the car repair business for about 20 years. Can you describe how I might flush my cooling system at home?

I had the exact same problem with my 98 Jimmy 4.3 and I took that to the dealer and it cost me $800 to have the heater core replaced. I would really rather not repeat that experience.

10-14-2004, 06:31 PM
Grab a prestone flush kit from your local auto parts dealer.

10-14-2004, 10:16 PM
Those prestone kit's aren't much more than dish soap.

Living 2 hours from any rad shop we take the rads out (after we drain it) set it down with the hose side up, and then pour 3/4 of a bottle of liquid draino in. Then we top it with water and let sit 2 or more hours. Then we dump it down the toilet. For the heater core we put junk hoses on and pour the rest of the draino inside, then fill it with water.

After we dump the draino just run clean water through until it runs clear. You'll be suprised how much crap comes out.

10-14-2004, 10:35 PM
Using drano on an automotive cooling system is pure stupid.

Draino will damage rubber seals, tubing and who knows what else in the engine.

Use a proper automotive flush if the prestone is not good enough for you but Draino is just plain over the top and not smart at all.

10-14-2004, 10:42 PM
I learned it from a frien if mine and I swear that it works. But we don't leave any rubber products that we are going to re-use on, and we flush the system really good with clean water afterwords. My last hotrod had a heater core that I couldn't replace, and it was the only way to clear it out. Prestone did nothing.

10-14-2004, 10:52 PM
Exactly, but you failed to tell anyone about you swapping out the hoses after.

I would never have Draino grace my cooling system EVER.

Not meant for anything but metal and plastic sewage pipes and not the rubber, copper, iron and aluminum in our engines.

10-15-2004, 08:37 PM
Between the plastic ends and the core are big rubber seals.

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