Help tracing coolant leak...

[GearHead7]

Hey guys, need some help here, hoping you can shine a light on the culprit for me.

Car- Audi 04' B6 1.8T

Situation- The car belongs to my sister, and is at the 120K mile mark and never had a timing belt replacement done, so I told her I would do it for her. The car was leaking from the rear coolant flange, so I replaced that so I could get the car to my house for the timing job. The day after I did the rear flange, her fuel rail depressurizing valve broke on the fuel rail. SO i order that part and I replaced it. In the process of replacing the fuel rail, I had accidentally broke the top inlet of the thermostat (trying to fight a stuck fuel injector) so the hose that runs off the top rail into the thermostat just broke and again, was leaking coolant.
At this point, Im getting frustrated and needed to get the car to my house for the timing job and not worry about anything else, so I had a used thermostat in my garage from my old B6 that wasn't broken, it was just a used part that I had replaced on my old car and instead of waiting 7 days for ordering another, I slapped that one on and got the car to my house with no issues.
I did the timing belt replacement job and I take the car for a test drive and I get a coolant warning, so I pop the hood and sure enough the resiovor is empty and I cant spot the leak or pinpoint it whats-so-ever. I realized that when the car is on an incline is when it leaks, when the car is perfectly even on the ground it does not leak, SO that seems a little weird. I can trace the leak from the bottom of the oil pan and I can see it is coming from the driver side of the engine at or about the thermostat location, I just don`t understand why it would not leak for a 30 mile drive and then suddenly start leaking the instant Im done with the timing job?
So even tho its a used part, I don`t really suspect it. I did just order another one just to make sure.
ANything else in that area?

[rocket1420]

The oil cooler (thing the oil filter screws onto) is in that area, but the typical fail mode for that part is for the coolant to leak into the oil. This causes no visible coolant leak, other than a low coolant level. I would pressurize the coolant system and pinpoint the leak

Could also be the J plug, which should be changed as general maintenance anyway. If the car is a keeper, you should probably go with the ECS aluminum one. Don't be surprised if the old one comes out in pieces.

If memory serves, there's an O-ring that seals the thermostat to the block. This could be an issue with the used one you installed.

[GearHead7]

great info there about the o-ring- I didnt even check to see or remove or anything about an O-ring. Ill look into the J-plug as well. Thanks thats a huge help. As for pressuring test- can i rent that tool from AUto-Zone? and would it have the AUDI/VW fitting?

[BARRY]

don't get frustrated...these cars have their quirks as far as things that need replacement, but all has been well documented. always best to change out all plastic items that bolt to the engine when you've elapsed 100k.

once you do things once or twice, it gets much faster after that. i can do a CCT in like 2-3 hours by myself at a steady pace.