Vehicle specs at the bottom of the post

Problem: It's 90 degrees outside, I've been driving around for an hour, it's been idling for 20 minutes, and I get no heat coming out from the vents. This was a real problem a few months ago when it was cold, and I've been saving and slowly making general repairs to prepare for winter.

More Info:
Before anything, I had noticed the heater not giving heat last winter. The winter before that I had plenty of heat.

Had a radiator leak about a month ago. $150 to rebuild it, $120 to buy a new one and replace it myself, so I chose the latter option. Bought a thermostat as well because it was only $10, knew I had a heater problem, and have always been told that it's probably a broken thermostat and/or coolant concentrated more than 50/50 (or that it's simply too cold outside).

Change the radiator, change the thermostat, do an as-thorough-as-I-can coolant flush, which I chose to do as follows (skip to next paragraph if you dont care) : Drain using radiator petcock, then disconnect upper and lower radiator hose and squeeze fluid out, reconnect and fill again with distilled water, turn engine on with heater all the way up (fan on low) and top off radiator, let it run with cap off for 15 minutes to coax air bubbles out, radiator cap on for 15 minutes, repeat.

When the draining fluid became shockingly more clear than the first gallon drained, I put a bottle of radiator flush detergent and water until full/no air, replaced cap and drove around for 2 hours, came back home and idled for 20 minutes and... no heat. New thermostat, distilled water and about a pint of detergent, 90 degrees outside, engine is a peg below 210 degs Fahrenheit, and no heat coming from the heater. Yes I checked it wasn't on A/C and that the dial was turned to red.

Blower works fine, A/C works fine though. Quite frankly, I'm having a hard time believing the engine is less than 210 degrees in this heat and with no coolant inside. Any suggestions? The only thing I could think of was a dead relay, but I thought the heater and blower used the same relay, and that the blower wouldn't work if that was dead and it's working fine. Or maybe something else is forcing air out of my vents? What do I know.

Recent Maintenance:
About 4 months ago I had the mass air flow sensor completely changed out (spraying the holy hell out of it did nothing). I get the throttle body cleaned every year, the oil gets changed every 5,000 miles maximum, I change the fuel filter three times a year and the air filter every two months. At the same time of the MAFS change, I also changed the spark plugs. I'll test the spark plugs in a few days, maybe ones not firing, but I can't hear that difference right now and it'd be fairly noticeable. It just turned 125,000 miles last week.

Vehicle: 2001 Chevrolet Blazer. 2-door, 2 wheel drive. 5-speed manual transmission, no back windshield wiper (most of the Blazers I see around town have 4 doors with a back wiper). It has a plug outlet on the front bumper which I've never investigated, but have always assumed the vehicle was originally purchased/manufactured in the north and that the outlet is part of an engine block warmer. For some reason, I've had two mechanics willing to give me about $9000 for it (I take good care of this thing, but that's still way above its blue book) after they realized it was a five gear manual, or maybe they saw something else too but only mentioned the gear shift during their excitement. I have no clue why this is special, if you have any clue or can find one, message me.

 

Backflush the heater core. pickup 2 short pieces of heater core hose,bottle of CLR and a can of compressed air or if you have air tools cool.

Remove both hoses from the core (passenger side of the engine bay,against the firewall. you'll see 2 rubber hoses.

Place the 2 short pieces (one for the hose pipe to stuff into,the other to stick over the side of the fender)

blow as much water out as you can with the air. Pour the clr into the core. Try to get in as much as possible. Let it sit for a hour.


Stab the hose in it and Turn the hose on and flush it out.

 

I will do that post haste (Wednesday?).

Your signature, Chris015, flowed perfectly with your post, kudos.

Would this also be the reason why in such heat, run time, and with no coolant (only water), that the engine temp gauge would read below 210? I mean, I'm going to do it anyway because it's a 12 year old vehicle and that's never been done to it and seems like preventative maintenance, but if I need to replace something else to get the gauge to show the correct temperature I may as well do it all at once (assuming it's not displaying the correct temperature, of course. All the other gauges work so I assume it does even if the circumstances perplex me).