It's that time of year again, let's fix this no heat issue once and for all
 

Alright, so my car went from giving little heat at idle last winter, to now giving no heat. Let's cut the bull and get right to the crux of the issue. I think I have read every thread on this topic known to man, and if I'm correct, this is my understanding of the possible causes.

Assuming that the engine comes up to operating temp normally according to the gauge(thus ruling out a bad thermostat):

1) If the intake hose(the one on the driver's side) of the heater core is hot, but the output hose is cold or lukewarm, then the cause is either a plugged heater core or air in the cooling system.

2) If both intake and output hoses are hot, then that means circulation is getting through the heater core, and the main cause of the no heat situation is either the blend door not working correctly, or air in the cooling system.

My car is giving symptoms from number 1 above. Thus, I most likely have a plugged heater core, or possibly air in the cooling system, or both. I had the heater core replaced by the dealer at 73k miles, and it now has 124k miles.

My Audi mechanic, after trying many different solvents to clean out the heater core, told me the best one at getting it clean is "Sno-Bol" toilet cleaner. Now, assuming that I backflush my heater core using this, and then making sure that I flush it profusely with clean water to remove all residue of the Sno-Bol.... does anyone want to talk me out of using it this weekend?

Furthermore, when I drained and filled my cooling system this summer and filled it with new G12, the Bentley guide showed a couple of bleed screws that a person should unscrew to make sure that the system was bled correctly. On my 2.8L AHA, I couldn't find these. Has anyone had success using them to bleed the system? I ended up just leaving the cap off the reservoir and letting the car run for 15 mins with the heater on "HI".

Sorry for the long-winded post, but I just wanted to make this as plain and simple as possible for the legions of B5 owners out there that are afflicted with NHS(no heat syndrome).

If I've left out any other strong possibilities, I would appreciate if someone would contradict me in this thread.

keeping an eye on this thread to see how the "Sno-Bowl" works out.

I find my heat problem is oftentimes RPM dependent. At idle I get lukewarm air at best. Under acceleration or cruising RPMs (2K ish) the heat works fine. I've had a few good, trustworthy mechanics give me differing opinions on whether it is a heater core problem or not (half say yes, the other half say no).

to add to the list, another cause of temperature regulation problems is the inside and outside air temperature sensors.

Didn't Jeremy (ImTheDevil) threaten to put up a heater core flush guide using two 2 liter bottles and CLR (or limeaway or something similar)? I don't think I ever saw it.

deleted

My heat used to be RPM dependent, too. But that was last year. Now, it's just cold. Higher RPM's no longer affect the heat temp.

I used Jeremy's "two 2 liter bottle with CLR" method last November, but I didn't get any gunk out of the core.

I did learn, however, that pouring boiling water into empty 2 liter pop bottles makes them shrink to half their original size! :p

Outside & inside air temp sensors? Where do they live? Is the outside air temp sensor the one that lives in front of the radiator?

deleted

The outside sensor can be considered fine as long as it's displaying the correct outside temp in the dash, right? If so, my outside sensor is fine.

Not sure about the inside sensor, though.

Incidentally, I just ordered a new Radeon 6950 2 GB video card for my gaming PC. If I can't get this problem solved, I suppose I could just plug my PC into the cigarette lighter using an adapter and use the exhaust from the case to heat the car. :D

The heater core flush is really simple and can even be done with a garden hose if you don't feel like dicking with 2 liter bottles and CLR.

deleted

Honestly remove the heater core hoses take 5/8" ID (I think) clear rubber hose. You'll need two 6' lengths. Attach each hose to the heater core. For the garden hose side, soften the mouth of the hose with a plumber's torch so you can force the sprayer head into the mouth of the hose. Use the cheapo silver trigger head so it'll fit in. The big multi-nozzle sprayers might not work as well. After you've done all that, lead the outlet side to an appropriate drain spot (e.g. floor drain, bucket, outside), make sure the hose head is in snug, then let her rip. You'll see a bunch of white shit come pouring out and make sure you spray in from both the inlet and outlet side.

related, i think
 

I recently bought a 2000 v6 and when I test drove it, I swear it had heat, but it was 90 degrees outside, so maybe I missed it. Anyways, I have no heat. So I decided to start with the CLR flush method, and did indeed get some minor flakes and stuff out. But I doubt that was the problem, since it seems to flow pretty good with the garden hose to it.

I put the hoses back on, and tried to bleed, but no coolant comes out near the core, so I pulled the hose completely off, and no matter what, coolant is not coming out of the return pipe with the engine running.

Also probably related, the electric fan is on if the car is on. Shouldn't that only come on if the coolant is hot? I figure it may be the temp sensor for the fan, but what about the no coolant at the core?

The temp gauge reads right in the middle after about ten minutes, but the oil temp seems like it takes a long time to come up, like 20 minutes.

Advice?

Thanks

Ian