clog in the heater core?

99 silverado 5.3

My heater barely blows any heat. Sometimes it feels like room temperature at best. If I turn the fan off then back on it sometimes will get hot but the heat only lasts for a few seconds before it goes back to blowing "cold." I checked the (2) hoses under the hood and 1 is hot and the other not even warm.

Is this indicative of a bad heater core or one that just needs to be flushed out? I've heard of disconnecting the hoses and flushing water back and forth to remove any clogs (actually did that once before and it worked quite well). Does this mean that my heater core is bad or that it just needs flushing? I wonder if it's because someone mixed green and red antifreeze and it's gelled?

Should I have it flushed at a shop?

Yes I would flush your heater core. Pull both hoses and put pressure to the side that had the cooler hose. Then flush the entire cooling system to get any rust chunks out.

Yes I would flush your heater core. Pull both hoses and put pressure to the side that had the cooler hose. Then flush the entire cooling system to get any rust chunks out.

thanks! do I need to go both directions on each hose (towards the core and away)? When you say flush the entire system, do you mean the other hose or is there something else involved?

You can reverse the hoses for awhile- I've seen that help, if flushing doesn;t work.

You can reverse the hoses for awhile- I've seen that help, if flushing doesn;t work.

and one that's stopped working am I pretty much looking at a new heater core?

This has almost got to be this issue (and not blend door or something else) if one hose is hot and the other not, right?

#1 you run the engine on a cold start with pressure cap off. then that removes AIR which is also a cause of poor heat .. then you check that BOTH hoses are HOT if so the heater core is not restricted good flow that means a temp door issue.

IF ONE HOSE HOT THE OTHER WARM/COLD THEN YOU FLUSH THE HEATER CORE !!!

you remove hoses at the engine NOT fire wall or sh*t will happen .. you then using a water hose apply water in one hose with the other in bucket.. you then swap hoses and repeat until the water flowing out of the heater core is clear.. .. then you blow out all that dirty drinking water..tap drinking water will cause these heater problems ..

hook it all up then do the air bled process and check that both hoses hot then you should get heat back...

never use drinking/tap water only distilled water .. purchase antifreeze 100% then buy distilled water for $1 a gallon not $12 gallon ............

do not use more than 10-15 psi of water pressure .. because if its restricted with higher pressure stuff can break.

#1 you run the engine on a cold start with pressure cap off. then that removes AIR which is also a cause of poor heat .. then you check that BOTH hoses are HOT if so the heater core is not restricted good flow that means a temp door issue.

IF ONE HOSE HOT THE OTHER WARM/COLD THEN YOU FLUSH THE HEATER CORE !!!

you remove hoses at the engine NOT fire wall or sh*t will happen .. you then using a water hose apply water in one hose with the other in bucket.. you then swap hoses and repeat until the water flowing out of the heater core is clear.. .. then you blow out all that dirty drinking water..tap drinking water will cause these heater problems ..

hook it all up then do the air bled process and check that both hoses hot then you should get heat back...

never use drinking/tap water only distilled water .. purchase antifreeze 100% then buy distilled water for $1 a gallon not $12 gallon ............

do not use more than 10-15 psi of water pressure .. because if its restricted with higher pressure stuff can break.

great response thanks!

We had previously cut the hoses about a foot away from the firewall and used connectors to reattach them. This time I just unscrewed the clamps and blew water up into each hose (towards the firewall). Did this a couple times. Reconnected hoses and took off (I'll probably need to add some antifreeze tomorrow. In any case, the heat blows very hot now.

I had gone to a tire shop and they used some green antifreeze to my red to get it up to the correct level (this was a month or so ago). I've read on the bottles that you can mix "with any color" but I still think that's part of the problem, causing the two to gel up.

So, I shouldn't use tap water at all in the system? I never knew that. I may drain it completely and start over fresh with distilled water and dexcool (not a mixture of dex and green!).

Do you suppose that I should take it to a shop and have it flushed or could I just go to the car wash and blow the core out again, let it all drain out, then refill?