Audi A6: Twin turbo failure from coked oil feed lines and screens (2.7T biturbo)
Twin turbo failure from coked oil feed lines and screens (2.7T biturbo) is a common engine fault on the Audi A6 on the 1999–2004 cars, and we rate it critical. Putting it right costs $5,000 to $10,000 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 34 documented faults on the Audi A6.
- Vehicle
- Audi A6
- Only on
- Bi-Turbo / twin-turbo
- Engine
- 2.7L
- Years
- 1999–2004
- Fuel
- petrol
- System
- Engine
What you are looking at
No photograph available
What goes wrong
The 2.7T biturbo used in the A6 and allroad has two small K03-family turbos buried low in the engine bay. On 2000 to 2002 cars the turbo oil feed lines were small in diameter and have a fine screen in the banjo fitting that clogs with coked oil, starving the turbos so the shafts wear, smoke and eventually fail. Audi fitted larger lines from 2003. Replacing the turbos is a big job because the engine usually has to come forward or out, so it is typically done as a pair with new oil lines.
What you would notice
- Blue or grey smoke from the exhaust on acceleration or after idling
- Whistling or siren noise that rises with boost
- Low power or limp mode on hard acceleration
- Oil consumption with no visible leaks
How to check it
Where to look. Low down on each side of the V6 engine, behind the exhaust manifolds; oil feed lines run from the block to each turbo
Ask for invoices showing turbos or turbo oil lines have been replaced and whether the newer larger-diameter feed lines were fitted. From cold, have someone watch the exhaust while you start the car and again after idling for a minute then accelerating hard: blue smoke is a bad sign. On the test drive, listen for a whistle or siren sound under boost and feel for boost coming in smoothly and strongly. Check the dipstick for low oil. If a workshop inspection is possible: check shaft play in both turbos, boost pressure on a logged drive, and the oil feed banjo screens.
What it costs to put right
$5,000 to $10,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.
Ask the seller
- “Have the turbos ever been replaced, and when?”
- “Were the turbo oil feed lines and banjo screens replaced or upgraded?”
- “Do you let the engine idle for a moment before switching off after a hard drive?”
Now check the Audi A6 you are actually looking at
Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.
Where this comes from
- AudiWorld: 2.7T V6 forum, turbo oil feed line and coking threads
- Audizine: An oil screen hypothesis (2.7T turbo banjo screens)
- Euro Premium Parts: Audi A6 C5 Reliability Guide (2.7T biturbo turbo failures)
- Bob Is The Oil Guy forum: Turbo coking... when?
Audi A6 buyer questions
Is twin turbo failure from coked oil feed lines and screens (2.7t biturbo) serious on a Audi A6?
We rate it critical and common on the Audi A6. The 2.7T biturbo used in the A6 and allroad has two small K03-family turbos buried low in the engine bay. On 2000 to 2002 cars the turbo oil feed lines were small in diameter and have a fine screen in the banjo fitting that clogs with coked oil, starving the turbos so the shafts wear, smoke and eventually fail. Audi fitted larger lines from 2003. Replacing the turbos is a big job because the engine usually has to come forward or out, so it is typically done as a pair with new oil lines.
How much does it cost to fix on a Audi A6?
$5,000 to $10,000 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.
Which Audi A6 years are affected?
Our research records this fault on the 1999–2004 Audi A6. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.
How do I check for it before I buy?
Ask for invoices showing turbos or turbo oil lines have been replaced and whether the newer larger-diameter feed lines were fitted. From cold, have someone watch the exhaust while you start the car and again after idling for a minute then accelerating hard: blue smoke is a bad sign. On the test drive, listen for a whistle or siren sound under boost and feel for boost coming in smoothly and strongly. Check the dipstick for low oil. If a workshop inspection is possible: check shaft play in both turbos, boost pressure on a logged drive, and the oil feed banjo screens. Look here: Low down on each side of the V6 engine, behind the exhaust manifolds; oil feed lines run from the block to each turbo