Need opinions please, heater core replacement? long

[Randolph]

When I drive the Audi in the cold weather I usually get foggy windows after I've been in the car for about 15 minutes. I figured I must have a bad recir spring, nope mine is in perfect shape and that whole assembly looks like it's never been broke. When the windows fog up I have leaned over and reached under the dash to make sure the recir door is closed and it always is. The car is dry and does not leak any water. It never does this in the warm weather most likely because flow to the core is off since I have the A/C on. I've come to the conclusion that I must need a heater core. The thing is this........I would prefer the car gave me more confirmation that it is indeed a bad heater core. I don't have a greasy film on the windows, no significant coolant loss (have to top off maybe every 1,500 miles about a 1/2cup) and if I keep the heat set at 90 the windows actually stay fairly clear. I've even licked the inside windows (making a fool out of myself) to see it they tasted like coolant and the don't. You would think that if I turned on defrost and set the temp on "hi" I'd get condensation building up on the glass but I don't. Could the leak just be that small? This is a job I actually want to do myself if it needs to be done. I'm already thinking new blower, new core, new seals, clean out god know's what that is under there etc, etc. So anyway what do you guy think based on my description? Does it need one or not. I'm tired of foggy windows, it makes me feel like I'm driving a POS when it happens. TIA Randolph 87 5KCSTQ 93 928GTS

[tonyj]

wanting to close it if no vacuum opens it.

Your problem might be that the vacuum line is off the recirc door actuator or that the controller is not telling it ot open when it should.

I would grab for ANY straw before attempting the heater core.

Another thought. Try some Bars All stop leak. If a heater core leak it will fill it. We did this on my son's 98 A4 two years ago and it has been fine ever since.

[SmellenDelicious]

should be removing the moisture from the cabin. On Hondas, the AC kicks on on defrost for the same purpose, removing the moisture.

[Randolph]

When I say the door is closed I mean its closed from the inside of the car (under the glove box) meaning its drawing in fresh air right? I'll check that spring and vac line again just to be sure. So if it's open on the inside of the car its closed on the engine compartment side and vice versa. I think this is the correct operation no? Thanks
Randolph

[Taylor 865KS]

heater core is leaking. What about hooking up a high pressure water hose to the ingress of the core after plugging the hose at the egress ? This shouuld show if it is leaking hopefully by looking at it through the flapper door or seeing if it drips onto the ground under the car. Another off the wall idea would be to find a way to force the same kind of dyed gas that is used to check leaking a/c condensers with a black light through the core.
Given the very small amount of coolant you lose and the Audilingus you bravely performed I personally don't think that a leaking core is your problem. You could be losing that half cup as ultra slow leaks from a dozen different hoses / clamps . Gawdknows, my car takes more leaks than a drunk in an alley.
As someone in a recent previous post wisely commented the type 44's are built around the heater core so you certainly want to be sure it's breached before replacing it.

[Will Ng]