Oh.. and also there is no frothy oil cap nor smoke coming from the tailpipe ... engine runs smoothly... so I'm not thinking its a blown head gasket either...

It looks like either all the old coolant wasn't out when the new was added, or there has been more pink fluid added. It can't be oil- it won't mix into the water and just floats on top. The tranny cooler is part of the radiator, and you do need to jack the car up to check the fluid level. You also need your VCDS hooked up to the car to check the fluid temp to get the correct reading. There is something that looks like a drain plug on the bottom of the trans pan. It isn't a drain, you remove it to check the level and add fluid with a pump.

To get every drop out a flushing machine would be best. Many shops don't have one, the places that usually do are places that sell a lot of "wallet flushes". (big chains running specials come to mind) The other problem with a flushing machine is that they don't have 5 different tanks for 5 coolants, just one that gets filled with X type.

With that stated, removing the radiator AND taking the drain plug out of the block AND taking a heater core hose off to pre-fill it with the new coolant should take all but a tiny amount off the old coolant out. A word of caution on the heater hose though...Your car is a couple years older than mine and mine didn't like the hoses on the heater core being messed with when I swapped engines. The core pipes are plastic and mine have developed a stress fracture-I'm going to wait for it to blow to replace it. I'd probably just live with the pint that stays in the heater core, it won't make a noticeable difference in the coolant especially since you've already had the fluid changed once. Same with anything in the turbo if your car is a 1.8. Getting the block drain plug out will make the biggest difference.

The only coolant that has been added is a small amount of my own 50/50 mix of Pentosin G11 with distilled water. I hear mention of the heater core flush.. That item along with the evaporator, a/c compressor, a/c lines, orifice tube & dryer accumulator we're replaced back in April. Could this grayish tint be something that is from the new heater core?? I have no idea what the pinkish tone is unless my Pentosin G11 is different than the blue stuff they used at the shop that refilled in back in April.

The reason I am replacing the radiator is because it is scaling on the outside edges from a slow leak on the drivers side upper corner that has been previously mended by the prior owner by what looks like some sort of apoxy resin... this apoxy also is a grayish color... could that be the reason I have a gray color in my fluid?

UPDATE ON COOLANT..... Just had system flushed and changed, apparently it was a stop leak product from the previous owner wearing off turning the fluid a strange color. Now there is a very slow leak coming from somewhere above the oil pan... the skid guard has been removed from my car and the lower oil pan is where I am noticing a slow drip... ONLY WHEN IT SITS OVERNIGHT AND HAS A CHANCE TO COOL.... I have pan underneath and am loosing a very small on the pan in the morning ..maybe 1/4 ounce at most.... When driving at temperature there is no leaking.

My mechanic cannot locate the leak so I'm wondering if I should put half a bottle of BARS heavy duty stop leak back in the system since this leak is impossible to find without ripping the front end off. I'm very leery of doing this although I've read several posts on other audi forums that says it will/can work for those impossible to find leaks in the system.

QUESTION NOW.... It says to put the product directly into the radiator and to my knowledge that would require draining the system YET AGAIN...which is a pain in the *** because my shop never keeps G11 or G12 on hand and its just more hassle than I want to deal with right now.. UNLESS I HAVE TO.... Can you not add half of the bottle to the resevoir when its warm... not hot of course... but warm... so as to melt the little particles??? The bottle states use the whole thing for 6 and 8 cylinder engines but my understanding is to use as little as possible to get the job done..

YES OR NO TO THE STOP LEAK????

Yeah.. I don't think I'm gonna use the stop leak... to scary!!.. Also, its WEIRD.. it doesn't leak all the time, i noticed a leak 5 mornings ago.. put the pan underneath.. the next day 1/4 ounce leak at most... the next 3 days and after a 200 mile trip I had to take.. NO LEAKS... then all of sudden this morning again it leaked again about 1/4 ounce or less the pan I have underneath.

My oil cooler and pressure switch is virtually brand new being replaced no more than 15,000 miles ago and the leak is more on the passenger side of the oil pan, say maybe a inch over from the far passenger side edge of the oil pan. I'm going to keep an eye on it to see if it stops again for a few days.. Ever heard of strange leaks that seemingly stop then start again?? I've only had to top off the coolant very little since the flush since it probably a burped so I don't think I'm losing much.

*** I hopes it not the water pump!!.. that was just replaced with the timing belt and pulleys at 143,000 and i'm now just at 178,000. I'm taking it to my 2nd choice Import Shop ( that's overpriced ) for a pressure test and evaluation next week to locate the problem. I'm hoping since its only SLIGHTLY leaking when the engine is dead cold and NOT WHEN ITS OPERATING that its just a loose clamp or a pinhole leak somewhere.

I'm keeping my eye on the coolant and as of this morning there was again a very faint puddle in the drain pan and the coolant resevoir was just above the MIN line when dead cold and at operating temps right at MAX. I'm just gonna watch it everyday ( add G11/distilled when needed ) until I take it in next week. I think it should be ok unless the leak blows out larger.

Did you check your coolant sender? It is located on the passenger side, and if it is not seated correctly, or the seal is bad, it will drip coolant. It is practically a wear item on our Audis anyway, so it would be good to replace it.