pylot

I've been having a vexing problem on my 2001 LS with 160555 miles. I've had several winters where I've had little to no heat. What's weird is that when it's warm (50+), my heat is usually pretty good (not as good as it should be though). When it drops into the 30's and below, it's anemic and sometimes is absolutely zero.

Things that have been done to the car that relate to the HVAC system recently:

• Flushed heater core several times (mostly clean, no rust and good flow) - hoses are warm (not hot like radiator hoses)
• Replaced top Quick-Lock hose connector to heater core (old one cracked when taking off hose)
• New water pump (proactively changed at 160k miles a few weeks ago), it was free so why not - new GM style
• New serpentine belt (Goodyear Gator)
• New radiator hoses
• New s-bend hose at top engine by bleeder valve
• Checked for air in system at bleeder valve
• Thermostat changed at 60k miles during intake manifold gasket change
• Flush of system (twice over the last 3 years) - filled with DexCool

If I do get any heat, it's only when I'm on low fan, and maybe an outlet temp of 60-65. At higher fan speeds, the heat is sucked out of the heater core faster than it goes in so it blows cold.

I visually checked the heater blend door actuator and it's working (at least the shaft is turning - I didn't remove it).

One odd symptom is that when the heater **** is all the way on hot, the air flow is about 1/2 that when it's all the way on cold (one reason I checked the actuator). Airflow with temp **** set to cold is good. This is with the fan or without (just letting the air flow as I'm driving). AC compressor was replaced about a month ago (clutch was failing and making me sound like a freight train, but otherwise AC system was good).

I did also check the fan while I had the glove box out and it was clean and rotated freely by hand.

Of note, first time I noticed it was when I had a flush at 100k miles (done by a mechanic at work). I checked for air and also flushed my heater core and it got better for a bit.

This is really no fun. I live in the northeast and when it's 10 degrees out, it's like driving a freezer to work (45 minutes). Driving to VA last weekend was even worse - 6 hours without heat and it was about 45 degrees in the car.

Help heat me up! Thanks.

oldchevy

You stated that when you flushed the heater core it got better for a while. That is possibly your problem. A partially blocked heater core or a bad or sticking blend door.

Rednucleus

I assume your temp gauge shows you get up to normal operating temperature? Do your hoses hold good pressure when at operating temp. If so I too would vote for a heater core problem or actuator that controls water flow thru core. Any difference on air flow thru defrost vs floor?

bearbait

Had similar problem with S-10 Blazer years ago. Disconnected both heater core hoses. Attached short length of heater hose to garden hose with clamp and clamped other end of heater hose to heater core and flushed. Repeated on both ports on heater core. You wouldn't believe the crap that came out!! Put back together and unbelievable heat!
Worth a try. Good luck

pylot

An update to my plight (and success!)

Had a local tech school work on my car - they changed hoses, did a reverse flush (six times), and determined it was a clogged heater core. They spent 11 hours trying to get the steering wheel off the car so they could put in a new heater core (with all the correct tools, and GM certified mechanics trying), to no avail. They just couldn't get it off. I figured I'd just have to sell the car if I wanted heat.

So I started doing some research about flushing, and found a post somewhere about flushing with cascade dish washing powder. A bit more searching found that cascade was no longer very effective, and that using TSP (trisodium phosphate, which used to be in dish washing powder) might work. I was worried it might do more harm than good, and kept poking around, until I found that TSP is actually used as one ingredient in a military antifreeze for vehicles in extreme cold environments (up to -70F). Figured worst case I'm in the same situation, needing a new car if I want heat.

So I poured about a cup of TSP powder into my overflow bottle, and drove for a couple hundred miles. I then did a complete system flush. Low and behold, HEAT! Glorious HEAT! Tons of it. So hot that I can't leave it on the far right setting even with the fan off.

My theory is that when I had my intake manifold gasket leak, which manifested itself as sludge in my overflow bottle, it also clogged up my heater core. Flushes helped a little, opening a few passages, but not actually clearing the sludge away from the walls of the heater core. TSP is an industrial strength cleaner, and dissolved the oily sludge in the heater core, letting heat finally flow again. I haven't had the car in extreme cold, but did have it down to about 20F and still had heat to spare.

Thanks for the support, and hopefully my story will help someone in the future.

Rednucleus

So you should market your secret formula as a super duper radiator/heater core cleaner and retire comfortably on a quiet Caribbean island!
Wonder if this would be a smart maintenance procedure to do just before a routine coolant change for any vehicle?