Audi A4: Oil sludge, blocked oil pickup screen and coked turbo oil feed line (1.8T 20v AEB/APU/ANB)

The B5 A4 1.8T has a small sump and a turbo that cooks the oil, so if it was run on cheap conventional oil or long service intervals, sludge builds up. The sludge blocks the oil pickup screen in the sump and the thin turbo oil feed line cokes up inside while looking fine on the outside, starving the turbo and then the engine bearings. Ignored, it ends in a failed turbo or a spun bearing and a dead engine. Audi's own service guidance for 1.8T turbo failures from lack of lubrication calls for a new, revised oil feed line whenever the turbo is replaced; there is no active recall or warranty cover on cars this age.

• Oil pressure warning light flickering at idle when hot, or flashing with a buzzer
• Black tar like deposits under the oil filler cap
• Turbo whine or siren noise, or blue smoke from the exhaust
• Loss of boost and sluggish acceleration
• Engine knock or rattle once warm

With the engine off, remove the oil filler cap and shine a phone torch inside: shiny brown oil film is good, black tar or crusty sludge is a serious warning. Pull the dipstick and check the oil is not thick, gritty or overdue. Start the car and watch the oil light: it should go out within a second or two and never flicker at idle once the car is hot after the test drive. On the drive, listen for turbo whine and watch the mirror for blue smoke when you accelerate hard after idling. Ask for proof of regular oil changes with fully synthetic oil at 10,000 km or less. If a workshop inspection is possible: drop the sump to inspect the oil pickup screen, check oil pressure with a gauge when hot, and inspect or replace the turbo oil feed line and check turbo shaft play.

Parts involved: Turbocharger.

$600 to $7,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has it always had fully synthetic oil, and how often was it changed?”
• “Has the sump ever been dropped and the oil pickup cleaned?”
• “Has the turbo or turbo oil feed line ever been replaced?”
• “Has the oil light ever flickered?”

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

• vwtuning.co: The 7 Most Common Audi A4 B5 Engine Problems (engine oil sludge on the 1.8T)
• TorqueCars: Most common 1.8T problems and issues (oil pickup clogging)
• VWVortex thread: FULLY clogged oil feed line for 1.8t AEB
• VW/Audi TSB 99-001 turbocharger failure due to lack of lubrication (1.8L 5V turbo, revised oil feed line 058 145 778)