No Heat

Hi,
I have a 1999 Jimmy with computer climate control that is blowing cold air. I took it to a repair shop and they blew air through the heater core and it worked good for a while then cold air again. I have taken the hoses off the heater core and fluhed water through in both directions several times and it has good flow and I get good heat for a while afterwards. Could it be an air poket problem or a bad radiator cap? There is pressure when I take the cap off. This problem has been going on for about two years. It seems like the colder the weather, the colder the air from the heater. Thanks

Is the radiator and coolant reservior full. Does the engine reach operating temps of 180-210 degrees if not it could be a thermostat stuck in the open position. This would also cause poor gas mileage if the engine does not get to operating temp. Heater cores will either be plugged but you said it is not or leaking. On older style blazers and jimmys coolant/antifreeze leaked onto the passenger side carpet.

I had a similar problem in my 2000 jimmy, I live in northern Michigan and during the winter it gets pretty cold. I fought with it this fall and ended up first trying what you did by flushing out just the heater core. But it seems to work great for about a week then same problem again. Talked to a buddy at work about the problem and he told me that he has seen a lot of gmc car and trucks in the shop with the same problem. He recommended that I change the radiator fluid from orange (Dex-col) to green anti-freeze. So I did that and ever since it has worked great, also changed the thermostat at the same time. Now the heater gets such hot air that I only run it at 2 most of the time. Hope this helps you out.

I just fixed this same issue in my truck and it was caused by the intake manifold gaskets breaking down and clogging the heater core. I have since changed my gaskets and flushed and filled with Dexcool and have had heat for well over a month. I wouldn't suggest using the green coolant as these engines are designed for Dexcool.

I had the same problem several times with my 98 jimmy I ended up having the radiator flushed four times and finally a wad of something came out. No trouble for 3 years now

....Talked to a buddy at work about the problem and he told me that he has seen a lot of gmc car and trucks in the shop with the same problem. He recommended that I change the radiator fluid from orange (Dex-col) to green anti-freeze....

Cooling systems need to be maintained properly. If Dexcool systems are neglected, you will experience problems. If you use green ethylene glycol in a system that was designed for Dexcool, you're asking for more trouble, and you'll get it, guaranteed! Using it causes expensive ongoing problems that will continue to haunt you until you completely flush ALL of the green coolant out and replace it with Dexcool. Always use the coolant the engine was designed to use. Here is a great article that explains why NOT to change over from Dexcool to the Green ethylene glycol coolant.

http://free-auto-repair-advice.blogspot.com/search/label/Dex-Cool