Heres the issue guys.

My wifes 01 blazer was having this same problem last winter. She didn't get a chance to take it to a mechanic until march or so. By that time the weather was nice and warm so there was no need for the heater. (it did work when we tested it)

The heater wasnt used until now here in Dallas tx. the weather is beginning to get pretty cold.
We just had a baby girl 3 weeks ago, and driving around in cold *** weather in a non heated vehicle is bad enough for my wife, but worse for our infant baby girl.

Anyhow, Last year I bought one of those flush kits they sell @ autozone, where you cut the inlet hose for the heater core and t-off a fitting to connect a waterhose to it to flush the water out. It was very dirty, but after all that work outside in 10* degree weather my hands were freezing and i could hardly work around the car & it started raining. It was a pain in the butt, & after all that work the heater still didnt work.

We'll we now have a house/garage where I can get to some diagnostics on the problem.

I have worked on mustangs for the past 9 years or so. I know all the lil tricks on working on 289/302/351winsor based motors. and my way around 95 and down stangs.

I know really Nothing about chevys other than just the basic stuff youd find the same on a mustang I guess.

What are the know issues on these trucks? There is also another problem where when you drive the truck or turn it off at times it makes like a rumbling noise that sounds like it comes out of the muffler or catalytic converter. I've cleaned out the MAF sensor and changed the wires and plugs on it. (but right now its not running too too bad, main issue is the heat)

I came across this forum last year when i was going to check out her truck but i couldnt find it anymore. I've seen you guys give some very good advise so I thank you guys in advance.

-tony

 

just a thought, have a 96 gmc p/u 4.3, it was the thermostat , ck your water temp or htr hoses, are they getting hot?

 

sometimes the temperature will go up a lil but thats not very frequent.

 

The most common ailment of the Blazer family related to "no heat" is a plugged heater core. The first order of business is a reverse flush of the core. I do mine from the heater outlet connection and I've concocted a hose assembly to connect a garden hose directly to the heater core. I usually blow out the core into a milk jug and check for "sediment plugs". I once blew out a plug a 1/2" thick.

The easiest diagnostic for a plugged heater core is to grab the lines going to the heater core itself. If one line (the inlet) is HOT and the other (the outlet) is NOT, then the core is plugged. Reverse flushing should resolve the problem.

If both lines are hot, then you may have a problem with your HVAC controls in the dash. Could have a disconnected vacuum line or a faulty vacuum switch which controls the blend door.

If the heater core inlet hose is not hot, then replace the thermostat.

Check your coolant level with the vehicle cold. If the radiator is not full, fill it to capacity (preferably with the front of the vehicle elevated to drive out trapped air), fill the radiator with engine running and up to temp so the thermostat opens. Check your radiator (cold) the next day. If the coolant level has dropped appreciably, check your oil. Is it chocolate milky? If so, you have a blown intake manifold gasket and will need to have them replaced immediately. Coolant in the oil is never good for the main bearings.

The heating system on the Blazer is pretty simple, if you rule out the engine side of things, the only things left are the vacuum controls inside. Good Luck.

 

I had the same problem with no heat a year ago (2001 blazer), and it was indeed clogged. Had it flushed out and it worked great after that.

I have no heat once again. However, when I checked my overflow it was empty. I filled it up and continued to top it off until it stopped dropping, and then the heat came back. I checked it every day for a week and the level in the overflow was no longer dropping. After that I didn't check it for 2-3 weeks. Just the other day I lost heat again and when I checked, the overflow is completely empty. Thats a lot to drop all at once (might have happened over the course of a week...I'm not sure, since my wife had the car that week).

You said "check your oil. Is it chocolate milky?". Can you tell the color well enough from just whats on the dip stick, or do you need to drain it to tell (I haven't looked at it yet...my wife has the car again today). If it is the gasket, any idea how much it costs to replace?

I've been plagued by so many of the common problems with this truck recently. The heat diverter broke 2 years ago so I had no heat on the floor. Had the clunking ball joints fixed a year and a half ago. The irratic fuel gauge is an ongoing problem I've never fixed. The faulty ABS sensor showed up last year, so I just pulled the ABS fuse (so I have no cruise control now). Then this heater problem shows up, and now this morning it was very cold outside (20 degrees) and when she started the car the engine was ticking for about 20 seconds (still reading the forums for that problem...options so far: A/C clutch, lifters, PCV valve, and now head gasket).

 

I forgot to add: as I mentioned, the coolant level stayed the same for over a week when I drove the car, and didn't drop again until a week or 2 later when she took the car. The primary difference between when I drive and when she drives is that I only go about 5 miles to work on main roads, where as she drives 30-45 minutes, much of it on expressways. I don't know if that would cause you to suggest one possible cause is more likely.

P.S. I hope its not a problem that I'm hijacking this thread to ask about my own problem. Its a similar problem, and you already started to address the blown gasket issue. I'm not sure what ettiquette is for this board...post in a similar thread if possible, or always start your own thread for you own problem?

 

The blown intake manifold gasket can be a subtle problem, that being a slow leak of coolant into the oil, or a slow leak of coolant out of the engine. The tell tale whiff of coolant would be the tip off if the engine is leaking outward or you can pour a flourescent dye into the radiator and check for leaks with a black light (although some common leak areas are very hard to see even with a light). If you have "chocolate milky oil", you'll recognize it immediately on the dipstick, even more so if you used the die. On my vehicle, the dipstick glowed green. I had over a gallon of coolant in the oil (every radiator fill was dumping directly into the oil). I replaced the IMG's myself, took 12 hours, having to disassemble the top end to get to them. It's not a hard job, just takes a long time. You can cut the time down by half if you've done it before and don't get interuppted too often. A shop would charge anywhere from $500 to $1000 for the job. The parts only cost maybe $60.

 

This winter I had a problem with my 2002 blazer with no heat.
I went to this forum, and got some great advice. the heater core was not blocked as there was heat on both sides of the hoses, but when I checked the vacuum lines I found a 6" pigtail hanging free.
I went to the autozone looking for a schematic of the vacuum lines to see where it goes, but it was not in the book.
I asked the guy behind the counter at Auto Zone, and he said that if it was not in the Hanes or Chiltons books, I would have to buy a 3 volume service manual. $170! No way.

So one day, I spotted a guy sitting in his blazer talking on his phone. I interupted him and asked if I could see under his hood to trace a vacuum line. He just popped his hood and kept on talking. Rather nice. (my friend said I should have stolen his battery to show that no good deed goes unpunished ... but that's not me.)

SO ... I found where the errant vacuum hose went, plugged it in, and volia, heat!!!!

To honor the guy who let me peek under his hood, I have taken photos under my hood, and added diagrams to help others.

This is my best guess at a vacuum schmetic. us it at your own risk


Here is where the vacuum line starts at the manifold. this picture is taken with the cover off the throttle.






here you can follow the lines over the master cylender and to the drivers side.

 

to continue ...
here is where the lines cluster. there is a one way check valve and a few tee fittings.


Here is where my vacuum line was unplugged, there is a port or fitting under a bracket that is difficult to see.






The bracket is under what looks like part of the break system.


when I was done, it looked like this, but you need a mirror to see it.


I hope this helps others. I did a lot of searching looking for a vacuum schematic, and came up empty handed.

Hey, check out the plane I am building .... http://www.theaerodrome.com/forum/re...i-project.html

 

that hose that was unhooked on yours was pretty rotted on mine, so i replaced it, but where does it go after it disapears into the fender? I also have very little heat, but both my hoses are hot, and the vents seem to do what they are suppose to for the most part. I get lukewarm air most of the time. I have the computer climate control on my '98. I wonder if it could be a partially clogged core? I don't know how i will flush it, because i am in northern MN and we haven't seen temps above zero in awhile.