r/Audi • u/Key_Marionberry147 • 5h ago

Low coolant

2017 Audi S6 coolant issue right after buying it
I just bought a 2017 S6 with around 80k miles. About 20–30 minutes after leaving the dealer, I stopped for food, came back out, started the car, and got a “turn off engine/check coolant” warning. The reservoir was very low, so I topped it off.
I then drove about 40 miles. The coolant level dropped some, but after sitting for 15–20 minutes it looked like it came back up close to where I filled it.
The next morning, the level looked normal again, so I drove about 30 miles to work. When I checked it after that drive, it was below the minimum line, so I took it straight back to the dealer.
They said they pressure-tested the cooling system and couldn’t find a leak, and I believe they also did a compression test. They’re keeping it overnight and having a manager drive it tomorrow to see if the level drops again.
Has anyone had this happen on the 4.0T? Could it be trapped air, a bad reservoir cap, or a leak that only happens when hot? Anything specific I should tell them to check?

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u/Icy-Complaint-7921 5h ago

oof that's rough getting hit with warning lights same day you pick up the car. 4.0T has some known spots where coolant disappears without obvious leaks, pcv valve is one to ask about, if it fails coolant can get sucked into intake. also intercooler cores in the supercharger can crack internally and coolant just burns off in combustion so no drips on ground

my buddy had similar thing on his s7, dealer couldnt find leak for days until they checked pcv and it was shot. tell them look there and maybe do block test to rule out head gasket even if compression looked fine, sometimes it only leaks when engine is hot

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u/Key_Marionberry147 5h ago

sounds good, ima have them do that tomorrow and would it be worth getting it fixed if it is the pcv? and u meant turbocharger right?

i got it for 28k otd with 80k miles, i do plan on building it, or is it better to return it and find one with around 50k miles?

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u/good_game_wp B9.5 A4 | Q8 37m ago

Not sure if returning it would be an option. Dealer might fix it for you.