2002 Blazer 4dr 4x4 - No heat

Truck just turned over 75k miles. All winter long the one thing this truck did well is get heat to the coldest passengers. Then last week, with no signal of impending doom, all she does is blow cold air.
First thing I thought to check was the radiator. The 'overflow' tank (not sure that's what it's actually called) had nothing in it, so I let the engine cool and I opened the radiator cap. What I saw shocked me. Sludge on the cap. I thought it was a huge amount, but I wiped it off pretty easily then turned my attention inside. All I saw were rusted coils. No coolant. So that morning I brought it into a Tires Plus shop for a flush and fill (with chemical clean as they advertised it). I was hoping that the change would give me some heat (as it's turning cold up here in the midwest again). Not to mention clearing any residue out so it doesn't wreck the motor! First thing I tested that evening was the heat. Very little warmth coming out after driving the vehicle for 30 minutes. It seems to not overheat, never have I seen it get over 200 (usually about 180-190 I'm guessing). My oil pressure seems high (usually about 40), but I've changed the oil many times and it remains the same, so I'm guessing consistency is good (I'm no car expert though). Naturally that night I started checking the web out, and found out that systems with Dex-Cool from GM are ticking time bombs. I'm not sure what was in the radiator before (as I just purchased this car about 25k miles ago). From the sounds of it I'm hoping it wasn't this Dex-Cool. The shop I took it to put some generic fluid in and said it would be okay. And the press I'm reading agree as long as the system if flushed before the change is made. I knew the heater core could be the problem, but most of the articles I've read online said when you turn on defrost, you'll generally get a film of antifreeze on the window. That hasn't happened (but the antifreeze was low obviously). I'm going to do a good clean of the windows tonight and try that afterward. I don't smell anything 'sweet' while the defrost is on either. Is there any other way to check the Heater Core? From what I'm reading in the articles, I don't really want to just start throwing money at it if it's going to be a sludge problem. Cure the problem, then replace the parts me thinkst. I don't think the thermostat is bad as the engine shows no sign of overheating at this point - even when idling for 1/2 hour as a test. As a side note, late last summer the beast didn't throw as much cold air with the air conditioning either. But as winter was approaching, I really didn't think much of it and planned on having the airconditioning system checked out and recharged if necessary.
Any ideas on how I can make sure the radiator is clear of sludge before trying other things? I recall reading that there is powder chemical you can put into the radiator and drive around for 6 hours then flush and fill again. Anyone ever heard of that? If so, do you know it works? I'd much rather spend a cpl hundred repeatedly flushing/cleaning the system than replacing all the parts. Or is the wise move to get out from under this money trap ASAP? I can easily sell it for what I owe on it.
Thanks for any ideas.
Todd.
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On 5 Apr 2007 06:12:49 -0700, snipped-for-privacy@gmail.com wrote:

At this point I would suggest that for starters you pull the radiator and have it "boiled" out and cleaned at a radiator shop. Next reverse the hoses going to heater core to change coolant flow direction to help clean core if it is clogged. After replacing radiator after it has been cleaned I would flush system again to clean heater core (either that on have it removed and flushed too) EPA regulations have greatly limited the effectiveness of over the counter flushes these days and have radiator cleaned manually will mean the flush can focus on the rest of the system.. One the coolant, the problem is not so much Dexi as it is the engine itself. It has a mixure of metal in it (castiron and aluminum) which causes a galvanic reaction with coolant. With Dexi GM attempted to control this while still using a 50/50 mix which does not cut it long sometimes. When you replace coolant use at least a 60/40 mixture and your problem will not return. Also GM heater can be very sensitive to coolant level and can air lock and provide no heat if cooling system is not full. Sometimes it takes a few heat and cool cycles to purge the air from it. Using a 7 to ( pis cap will speed the purging process up some. (I use 7 to 9 PSI Stant caps all the time regulalry with 60/40 or 70/30 and I have never had any over heating issues or sludge build up issues and the first thing I do with any new car is increase the antifreeze consentration after I buy it) Sounds like previous owner did little more than drive it for a while and then dump it. ----------------- TheSnoMan.com
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Thank you for the quick reply. I truely appreciate it. I'll give it a shot this weekend. Have to take care of the baby!
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On Apr 5, 9:12 am, snipped-for-privacy@gmail.com wrote:

Todd, the thermostat can stick open as well as stick closed. If it sticks open the heater will blow luke warm at best.
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