Owned this car for 2 years, I have about 150k miles on it.
Within the last 2 weeks I have had a weird coolant issue twice.
Go to leave work after car sat for 8 hours.
See LOW COOLANT warning. Turn off car.
No puddle under my car.
Pop hood , see little or no coolant in reservoir. No signs of leak in engine bay.
Add 40 Oz of purified water to my reservoir.
Drove 7 miles home semi-hard to put pressure on my coolant.
Opened hood. My Houdini coolant has RETURNED TO MY RESERVOIR.
At this point the coolant is way over the max, so I open the cap and let the excess bubble out from the pressure increase.
I don't see any oil in my coolant or vice versa and no other signs of head gasket problems.
I ran a few searches on the forums using different terms but didn't find any post about this besides a B8 S4, which suggested water pump. Any help would be appreciated.
In case it may be of use, below is a list of my recent DIY work on it:
3 months ago:
Replaced both side valve covers and most of my coil packs.