I was disappointed in mine, so I took it apart and did it another way. I ran a garden hose from the laundry tub, out the window to the driveway, and back flused with the hottest water I could get through 75' of hose. Ran a lot of water through it and now I have good heat. Was it the combination of CLR Friday night and the back flushing today? Who knows. But here was my VAG-COM Friday, and now today. In both cases, heat is turned up all the way on "HI".



Significant temp difference in the outputs on that last line.

 

I'm glad both you guys made improvements on the heat!

 

I've read about keeping the air pressure to a minimum because of possible ruptures in the core resulting in greater problems. I've read elsewhere that the coolant runs through at about 10psi. Any suggestions on max. air pressure for blowing air through the core durning a heater core flush?

Also, any rule of thumb on the length of time the CLR can sit in the core before damage is done to it.

 

I let pure CLR sit in mine overnight. As far as I know that did no damage.

I'm not sure on your air pressure question. I read some on that too. I don't have air so didn't do that. It does seem to me that 10psi is not much when it is just passing through to an open end. If you blocked one end, the apparent pressure inside would be 10psi. But when the air is escaping, the apparent pressure in that core would be quite a bit less.

My bigger concern is the old, brittle plastic on those nipples coming out of the firewall. I split one of mine, but the split is under the hose after i pushed the hose on farther than its supposed to go.

 

The core's are not bullet proof, as noticed by cracking hoses, housings, etc...the 10psi is the MAX pressure you really should put through your core, closed or open system so as not to damage your core 'fins'. I HAVE done the heater core replacement, and it IS about a 11-13 hour job taking the dash out with the 500 zip ties behind it...LOL

Attached pictures of a heater core AFTER someone ran STOP LEAK through an audi........

 

10 psi it is then, no problem. And just to verify, undiluted CLR? I've read most people using a 50/50 mix with water. I don't mind doing straight CLR as long as it won't damage the core too much. I suppose that's the reason for my question, I want to be effective in the flush but I don't want to go overboard and create additional problems. I've tried flush/backflush already (in the dark with nothing more than my phone, not fun or advisable) but it didn't really work. Of course, I couldn't tell what psi the water pressure was running at. How does one tell water pressure from the hose? The problem I also encountered was, I don't feel I really accomplished bleeding the system. After one hour of trying to get fluid to spray out of the bleed hole with no success I figured the core must still be clogged and decided to try it again at a later time (when it was warmth and daylight was present.) I may not be getting both this weekend but at least I'm willing to take another pass at the whole process, this time with CLR, air pressure, light and time. I'll also take a screen shot of my VAG numbers before and after for comparison/additional help.
Thanks for the replies and I'm sorry to hijack the thread.

 

What motor do you have? Getting coolant out of that little hole in the heater hose is not hard at all.

 

1.8. I know "how" to do it (the process) but no coolant was coming out of the bleeder hole. I was running the heat (HI) for at least 40 minutes but nothing was coming out. The inlet hose was hot and eventually the outlet hose reached the same temperature. I figured there's still air in the heater core and/or a block within the core resulting in insufficient heat. I suppose I'll attempt to bleed the system (again) first and if that doesn't work, I'll proceed with CLR flush.

 

I think you're missing a step. When you are bleeding through the outlet hose (one on the left), someone needs to be in the car with rpms around 2000+ once the car is warmed up for it to come out of the little hole (remember it is a 'passive' system-if there's no pressure, it just flows through idly-that's why there's generally more heat when you're driving). IF your return/outlet hose is hot after awhile, then the coolant IS flowing through your heater core and you probably just have air in it. The 1.8 takes a little more time to bleed than the 2.8. I HAVE (not telling you to do this), when the car is sort of cooled down, poured coolant down the outlet hose until it came out of the top, then poured coolant down the inlet hose with the reservoir cap off (on the inlet hose you will see your reservoir start to rise while pouring...then put it back together, let it get to operating temp and bled it, it helps a bit.

People have done undiluted CLR and 50/50, I'd try the 50/50 first and let it sit overnight. Flushing it afterwards with a garden hose is fine and should get the job done, with a little mess of course. Make sure you get all the CLR out though, you really do not want that stuff floating around your cooling system.

 

Well, there's good news and then there's something other than good news. I made it to the store before they closed to pick up some CLR and misc. fittings to add to my flush setup. Got back to and decided to give bleeding the system a try again before proceeding.

While "bleeding" the system as described by markymarc I figured there a flaw in this approach. While my help was archiving the 2000+ rpm one must pay particular attention to the raised expansion tank. Again, nighttime is probably not the best time to do such procedure, even if one has "sufficient" garage lighting. Apparently, when engine rpm's increase, so does coolant flow, which is great for the heater core and cabin heat. However, if one is not paying particular attention to the expansion tank, coolant (not just air) is highly likely to bleed through overflow port (under/back side of tank) and from expansion tank cap that is loosely fitted. It doesn't take long to "bleed" 1 gallon of 50/50 mix of perfectly good/new coolant/water from the system, ask me how I know.
Without any additional g12, I added 1 gallon of distilled water to the system and continued to bleed the system. I managed to eventually do so successfully (that's what I'm calling it at this point) bleed the system of "most" air that restructed sufficient cabin heat. I managed to take a quick screenshot of before and after like from the mtroxel's post for comparission. Those will follow tomorrow when I can get them from my phone and onto a picture host.