Flushing the heater core

[Craig 94 TA GT]

Previously, my heater had just all of a sudden quit working. Well it was barely luke warm air when running at full temp. But just before, it was fine, blowing out hot air.

So I went ahead and flushed the heater core. Removed the 2 hoses on the left side of the water pump, bought an adapter for the garden hose, then flushed. Put it back together, and it works really well now - blows very hot air. I didn't get a chance to see what came out during the flush, as I routed the bottom hose to the ground, to make sure it's away from the opti. So I couldn't tell what was clogging it.

So my question is, is it common for it to be plugged one day and go from nice and warm to barely warm? Is it possible for, say, head gasket material, or any other foreign matter breaking up to clog it? I just want to make sure that this was caused by build-up, not by something breaking inside. Thanks for any advice.

[Wild Willy]

Not un-typical of a GM heater core- I have back-flushed a couple.

As to what causes it, could be many things- most likely sludge from broken down anti-freeze, maybe some rust or sediment. Could be sand left over from the casting of the block or heads- Has any one ever put any sealer in there for small leaks? Chunks of rubber from hoses breaking down? Too bad you didn't watch the outflow when you flushed it, might have told you more.

I have heard of people who have had this problem re-occurring to put an in-line filter, sort of like a big fuel filter. Probably someone had a bad casting....
I have never had the need to get that fussy-

[Rob B (shoebox)]

It is common for a 4th gen heater core to get clogged. Luckily, it is pretty easy to remedy.

[Jeff_in_Atl]

I just flushed mine last weekend. It's nice to have heat again.

[01Y87]

is it common for it to be plugged one day and go from nice and warm to barely warm?

Just as common as with people, one day you feel fine and the next day your artery gets plugged up and you get a heart attack and die. You never know what kind of junk is floating around in those narrow passages until one day it plugs up.

[Craig 94 TA GT]

Thanks guys, that's a good way to put it. I guess any coolant that was passing through made it warm...but once it clogged enough to have a lack of circulation, then heat will be gone. I just found it odd because the last time I did a full flush was back in '99 and had 0 problems since. I did change the coolant since then, but never flushed with a garden hose.

[ryan34]

It is common for a 4th gen heater core to get clogged. Luckily, it is pretty easy to remedy.

hey shoebox, do you have a write-up about it?

[Craig 94 TA GT]

It's simple. If you want to avoid a mess, drain the coolant (or at least enough to not have it spill all over the place when removing hoses from the water pump). Remove the 2 smaller hoses to the left (passenger's side) of the water pump. Put your garden hose in some kind of adapter (I made one from parts I found in my garage), and attach it to one of the hoses. Spray to flush thoroughly. You can reverse flush too if you'd like. Just make sure to get no water on the opti.