thesameguy

My '99 Avant 1.8t has been suffering weak heat for about a month. This is the first time in three years the heat has been an issue, but of course the heater sat unused for six months prior to this issue, so who knows what happened.

Before starting down this road I checked both hoses at the core, and both seemed plenty hot. I bled the system, a tiny bubble of air came out, but that was it - a steady stream of coolant followed. I messed with the climate control for a while - turning the temp up and down, etc. - then hooked up VCDS to see if any fault had been generated. None. I temporarily ruled out the blend door, then decided to flush the heater core.

Check out The Contraption®:



It consists of:

o Dewalt 2500rpm drill
o Harbor Freight "small" drill pump
o 15' of clear vinyl tubing
o Two pair (two male, two female) of 5/8" garden hose menders
o Two 3/4"->5/8" Dorman 47080 heater hose adapters
o ~16" of 3/4" ID silicone hose
o Pressure washer water filter
o Home Depot Bucket
o 2 gallons of distilled water
o Prestone Radiator Flush
o 4 long zip ties

Seeing as I had the drill and the bucket, I'm in this about $30. I was hoping to use the filter on the intake side of The Contraption®, but the crap ($2?) Harbor Freight drill pump doesn't generate enough suction to pull through the filter. That's actually why the bucket is tilted, too - not enough suction to lift the water 2'. Lame. Whatever, it was cheap. Thus, I put the filter on the output side - it does have an advantage which is that everything that comes out the heater core will get trapped in the filter for inspection.

I let it run through the heater core about 30 minutes in each direction. Gotta be honest, I was hoping for all manner of toxic waste to emerge from the core, but so far the results have been disappointing based on what's in the filter, and what I've seen traveling down the hoses - just a couple little black floaters but nothing serious. I'm going to leave it set up tonight with The Contraption® Solution® (that is, distilled water and Prestone Radiator Flush) sitting in the heater core to see if that does anything.

Based on what I'm seeing I'm a little baffled as to what the Audi's heat problem actually is. Seems like if the heater core was genuinely clogged, the wee little drill pump wouldn't be able to push anything through it, and that's not the case. There is good flow from the output. Seems like if the core was somewhat clogged, crap would be coming out of it, and that's not the case either. Sure seems like the heater core is in good shape, so now I don't know what the problem might be. My only guess is that the blend door isn't doing what it should *and* not triggering a fault, which seems unlikely... but I don't know what else to look at...

Any thoughts are appreciated, but I really just wanted to share The Contraption®.

thesameguy

This is the filter from The Contraption®:



It didn't catch some of the fantastically small particles - they end up as a ring around the bucket. None of this is even remotely enough to clog up a heater core. Given what I ran through it and for how long - Radiator Flush running for an hour or two plus an overnight soak, plus CLR for about two hours - I really think that any major clog would have made a bigger mess than this. Thus, my conclusion a clog is not the problem.

Prospeeder

if you saw what the inside of the cores look like you would see why flushing them doesnt do much, and why they clog. Replacment is the only option. And This is SOOOOOO common on A4 and Passats its not even funny. Every year here we get several of the weak/no heat passats and A4s as soon as winter hits. Flushing sometimes helps, but it usually doesnt. Just because it SEEMs to flow does not mean anything. I can guarantee you will run around checking other things and its just the core is done. When the temp flap is not moving the climate system will pick up on it and set a fault right away. The cores tubes just run up and down, its not like your flushing it and it is forcing the water through the entire thing, you might have a few tubes not clogged and it just runs right through them and right back out. And they have have what looks like a long twisted noodle in each tube to slow the water, stuff just pack in and turns hard as a rock, flushing, chemicals, ect will not touch this stuff.


The one A4 i just did a week or 2 ago, i flushed it and flushed it, and it seemed to flow great. but still just barley warm, weak weak heat.New core, hot as can be, and i pulled the core apart and found it full of rock hard debris packed in the "noodles". And this was a car that had only G12, only 90k miles, always serviced, tbelt and wp done at 80k and system flushed with fresh Audi/VW brand G12. If the thermostats warming the engine up to temp and the climate system has no faults the cores bad.

thesameguy

I really appreciate the feedback. The cooling system on this car is in tip top shape - 150k, but always G12 and flushed every two years. The coolant that originally came out of the core was perfectly clean. Everything else works - thermostat is a year old, VCDS diagnostics passes, etc. I have not yet driven the car to see if it is improved but based on all the other facts what you're saying about the core makes sense. The only thing that gives me pause is the suddenness of the problem. It worked perfectly six months ago. Seems crazy it could go from zero problem to all problem that quickly, but who knows.

thesameguy

I drove the car for the first time today, doing only about 12 miles on it. Heat seems fine to me, but I never drove it when it was "not working" so I can't compare. I will say it doesn't feel as hot as in my old Saab 900, but frankly nothing I've ever owned gets that hot. Performance seems similar to my XJR. :shrug: It's 55 degrees out (so says the dash), and heat started within 10 minutes of starting the car and stayed warm til I got where I was going. I don't know what that means, it's just my update.

I'm going to burp the system tonight. I previously found my OTC 7991 "Cooling System Pressure Tester" does an awesome job of this - just pressurize the system to 10lbs or so, then squeeze the spring clamp on the heater core inlet and outlet. Any air trapped up there is forced out instantly... just gotta mop up when done.

I will keep driving this car for another week or two and see if anything changes. It needs a new cat ($400, ouch), but once that's done and assuming there are no heat issues, it's gotta go. I will miss the car, but I don't have room for it.