Heater core flush results
 

I originally started my day attempting to do a complete cooling system flush with Prestone cooling system cleaner and EVERYTHING, but the Lower rad hose connection stopped me in my tracks. Being in the engineering trade, I get PISSED when a feature on a consumer product like this is NOT designed as simply as possible; a simple hose-clamp requiring a screwdriver, please?

But I digress: I shifted gears to simply flushing the heater core using the clear-hose on the inlet/outlet, and power-flushing thru with a garden hose.

First, it took me over half an hour to get the heater hoses OFF, because again, the inlet (lower) hose clamp was biased toward the battery and NOT the brake booster where there was more room to grab it. So I had to pull the BATTERY out to get to the hose clamp. I threw away both hose clamps and substituted good 'ol screwdriver-driven clamps.

So I first back-flushed and say a TON of sandy-gunk come out of the core into the catch bucket. Then I added a small amount of Prestone cleaner thru the inlet, then filled the rest of the core with near-boiling distilled water until it started to run out of the outlet hose (clear hose in the ONLY way to go doing this). I let it sit overnight.

Not sure if the overnight soak was even effective, but I back-flushed again and more gunk came out, this time "flaky" stuff. In the bucket, this flaky stuff crumbled into gritty, sandy stuff.

Backflushed, forward-flushed, back-flushed, etc, about 6 more times, and each time flaky stuff would come out on the FORWARD flush, but not the backflush. Hmmmm.

So anyway, when I decided I got all the flakes (there was a huge amount; clearly my core was clogged with this stuff), I put the hoses back on (and the battery back in), and tried to bleed the upper hose per the Bently manual, with the bled hole pulled slightly off to bleed it. I ran it until the engine was HOT (guage straight up), heater on full blast heat, and onle a few bubbles came out, then nothing. I eventually pulled the upper (outlet) hose completely off with the engine running, and there was NO flow thru the core. WTF??? Flowed fine when I was flushing it! And of course, there was no heat either, even though the inlet hose was getting hot.

So then I did what another poster here in this forum suggested, I swapped hoses Inlet/outlet, and since the bleed hole was now hidden, I said screw it and clamped it all together and just drove it down the highway.

HEAT, BLESSED HEAT!!!!!!

So I'm driving now with the hoses swapped, and there is heat. Why didn't the core flow in the proper direction? No clue, maybe I should've driven it with the hoses NOT swapped to see if it somehow flowed at highway speed? Who knows, all I know is after blowing most of a day, I now have heat.

And if I figure out how the lower rad hose comes off, I'll do that whole-system flush.

Hope this helps someone, bottom line is you don't HAVE to drop 5 bills (what my local Audi indie quoted me) to have the core flushed, and you might not have to have the core changed (1k + $$), if you try it yourself.

Going to try reverse the hoses this weekend. My AR had poor heat last winter, so flushed core and bled air out and heat worked. New year and new winter, and no heat again. Tried bleeding and got same results as you wiht little to no flow even with hose off. Next try is to reverse the hoses. Hope it works. Thanks for the write-up.

Appreciate the write up and I might have to use it soon.
Where is the heater core hose BTW?
A picture would be incredibly helpful!

Between the battery and the brake booster. You see 2 hoses going into the firewall. Upper hose will have a white circle on it with a hole in the middle. Need to remove the plastic that runs side to side over battery to gain access.

On my 2.7T (I haven't worked on the V8), the lower radiator hose doesn't require any tools to remove. Squeeze the wire catch with your hand and wiggle it loose. If it's been a while, it'll take some effort. You can pull out the temperature sensor down there to get nearly the same effect with less effort. Might be a good idea to have a spare O-ring on hand in case the old one is crunchy.

The chemicals you're looking for to clean the cooling system are wood bleach (oxalic acid) and washing soda. Ace Hardware carries wood bleach and some grocery stores have washing soda next to the Borax in laundry supplies.

Search here and on bobistheoilguy. Use the GM procedure, except drive it around instead of running the engine with the car static, the 2.7T doesn't like extended running without airflow. Turbos=hot. Just drive it for a few hours with the flush in it, then do the neutralizer & rinses. My allroad went from no heat to good heat, but it took several flushes, and the amount of gunk that came out was truly amazing. There's an allen drain bolt on the bottom of the engine as well. Kind of hard to reach. Mine was so gunked up, it wouldn't even drain under pressure at first. It looked like the PO had used mud-puddle water to fill the radiator. Like an old water heater.

I probably pushed through 100 gallons or more. Splice in the Prestone connector so you can hook the hose to it and flush it forward and backward. Don't worry about using distilled water or expensive coolant until the last few flushes unless you have to leave it out in freezing weather.

If the system won't push coolant out of the bleed hole, it's probably not full, or the coolant cap is shot. Sometimes you need to rev the motor up a little (~1500 rpm) to get the flow moving. Did you open the bleed screw at the front of the engine first?

It's possible that a previous wrencher put the hoses back on the heater core reversed. Anyone who would leave the clamps in a position that required removing the battery to access them probably made other mistakes as well.

Check the after-run thermo switch and temperature sender (and their O-rings) on the cross-pipe at the back of the heads. They live in a very inhospitable environment, being just above the exhaust manifolds.

Welcome to the hell that is a neglected cooling system on an allroad. It's nice once it's all fixed, though. I made the mistake of working my way up from plain water to the basic coolant flush, through the stronger flush a couple times, to finally doing the heavy duty 2-part stuff, and ended up spending a small fortune on coolant. Good Luck.

it works well, your wecome for the money that i saved ya, run it for a bit, and do the top flush method while she is runing and hot. most car washes have a catch system for your coolant......takes abot 10 minuets, change antifreeze temp to a different color like advanced auto yellow....


pentosin "sp" antifreeze is mineral based. ie its water mixed with something like marvel mystery oil.

Tried the reverse hoes trick and it worked like a charm. This is after going from ok heat while driving and none at idle. Bleeding did nothiing and couldn't get good flow. While i had the hoses off I flushed the core as well. Tons of crap came out and it was just flushed a year ago for the same problem. Hooked hoses back up reversed (no bleeding)and went for a drive. Great heat and even at idle. Odd how it makes so much of a difference.

yup,, im leaving backwards for a bit, not even interested to switch back.