heater

we replaced the thermostat because there was no heat. after replacing heat came back and was working fine. two weeks later and now no heat again . ideas would be great . it is blowing air fine just no heat . did it go bad again or could it be something else. thankyou in advance

try flushing the heater core. I had the same thing happen, flushed my heater core and it works perfectly.

How did you flush your core?

there are two hose connections on your firewall going to your heater core. On my 1996 4.3 there were on the left side of the engine if you are looking at the engine from the front. Disconnect both hoses and using a simple garden house put water into the top one until you see water coming out. Reverse it and do the same thing to the bottom one.

I have ran into the same problem last year. That engine has now been retired due to water in the oil pan. Before the engine finally blew up. I had the complete flush done at Precision Tune and what a joke, 90 bucks for nothing I had heat for about 3 days but problem returned. I really thought it was something to do with the heater core but now know it wasn't. The engine was replaced along with the radiator and problem solved, never touched the heater core after that. The culprit was the radiator. That 5 year antifreeze is a lie. The corrosion inside the radiator was terrible, that was the problem all along. microscopic pieces of rust blocking all the pathways of water flow. I suggest you replace your radiator which is not cheap but cheaper than the 3 grand it costed for the engine too. If you reach in and feel the two hoses sticking out of your firewall and both are hot with fluid, then your heater core is not blocked, that means fluid is circulating just fine through it, if the tube on the left is cold though, yes, your core is probably the problem. My guess is the radiator since most people dont change the 5year 50k antifreeze annually. You cannot flush the system enough to completely remove all the rust caused by that garbage so just replace the radiator.

I was having the same issue where suddenly the heater didn't produce any hot air. Once I flushed the core it worked great. I appreciate your help.

-James

You may run into a problem still though, they may do a flush and break free a lot of sludge from the heater core and radiator only to have more break free a couple days later and clog your parts up again. You could have your radiator dipped or replaced fairly cheap, that will ensure all the crap is removed from inside, the heater core however, major expense to even remove that but it may come down to that, it is just not economical to flush the heater core weekly in order to ensure all the crap is removed. Hooking a hose up to it does not put any pressure through the system, the only way to do that is to pay someone to do a pressurized flush. Again, that is just not economical since the first flush wont break everything free, more stuff will break free in the weeks to come causing more blockages.

Had many heater core problems with my 99 blazer.
Had a regular cooling system flush as well as a heater core flush. worked well for exactly 1 week.

GM recommends an acid flush and there is bulletin out on heater core problems and Dex Coolant. Always keep coolant topped up. Air in the cooling system due to low coolant causes the coolant to scale and sludge builds up.

Acid flush causes much loose large scales which are too heavy to get totally flushed from the system. Eventually they find there way to the heater core and plug things up.

I flushed my heater core weekly about 6 times before most of the crap was removed. Unfortunately you have a problem that can never be totally rectified. I challenge anyone to prove otherwise. I've got some extra hoses with quick release clamps that can be quickly clamped to the firewall to get this done quickly. It can be done in minus 20 degree weather in about 10 minutes with a garden hose. Takes 20 minutes to coil up the garden hose and haul it inside.

Good luck.

You can totally rectify the situation if you remove the heater core and radiator, flush the system, then place new radiator and heater core in. Once new system is in, I recommend running regular green anti freeze so that you dont get the problem again in the future.

Lets be realistic ... replacement of the cooling system is not a good answer. Here's why:
1. Cost of all parts.
2. Replacement of the heater core is huge as it requires complete removal of the dash from the vehicle. This means playing around with a dual airbag system that doesn't deploy during the procedure and can still effectively save your life when you are finished. Cost here is huge. This not a job for a do-it-yourselfer.
3. Lastly, replacing these parts does not mean that things will be fine when your done. There are large pieces of scale usually lying aroundor loose in the bottom of a passage in your engine block. If you think that a flush will rectify this, you are mistaken. These will never be totally be flushed out. They will however work there way towards your heater core during long drives.

Also, Have you actually had multiple experiences with replaceing the antifreeze with green. I've asked around about this (at least 6 professionals) at different radiator repair shops. The answer is that there is likely greater risk of leaving contaminants from the orange in the coolant system that will lead to green antifreeze problems. Rememmber the installed stop leak inside the engine is meant to work with orange antifreeze.

Not going to reply anymore to this as I'm done.
Weekly core flushes seem to have done the trick.
Amount of debris decreased to nothing. May have to do it again someday but it will be dealt with when necessary

my heater core dumped anti freeze in my floor board of my 96 blazer.. my dad and i tried to get to it to replace it.. but couldnt, its burried under the dash, way under the dash. the repair book didnt help any. anyone know where i can get some info on this?

thanks
J