The brief
This A6 had reached the point a high-mileage engine gets to, down on power, using oil between services, not as smooth or as crisp as it once was. Rather than chase one symptom at a time, the owner had it overhauled, the engine stripped, cleaned, and rebuilt properly. An engine that's done big miles wears in a hundred small ways at once, the rings and bores, the valve stem seals, the bearings, the gaskets, and carbon builds up on the valves and in the chambers. Each on its own is minor, together they add up to lost compression, oil burning, and a tired feel. An overhaul deals with all of it in one go, the worn parts renewed, the carbon cleaned out, and everything reassembled to factory spec, so the engine comes back with the performance, the reliability and the economy of a much younger one.
The diagnosis
Compression and leak-down tests and a strip-down confirmed the picture, worn rings and bores, tired valve stem seals letting oil past, worn bearings, hardened gaskets, and a heavy layer of carbon on the valves and in the chambers, all consistent with the mileage. The bottom end and the head were both due the full treatment. That's a full engine overhaul, the worn parts renewed, a holistic decarbonise before reassembly, and the whole engine rebuilt to spec, rather than patching one symptom and leaving the rest.
The work
The engine was removed and stripped to its components, every part cleaned and measured, the carbon removed from the valves and chambers, and the worn parts, rings, bearings, valve stem seals, gaskets and seals, renewed with genuine Audi-spec parts. It was reassembled with care, every clearance and torque to the manual figures, refitted to the car, and run in with fresh oil and filter. The adaptations were reset so it relearns on a fresh engine. A road test confirmed strong, smooth power, a clean idle, no oil burning, and no warning lights.
The outcome
Strong, smooth power back, a clean idle, no oil between services, fuel economy back where it should be, and no warning lights. The A6 went home running like a much newer car. An overhaul done properly, with the carbon cleaned out and the worn parts renewed, resets the engine rather than buying a few months at a time, which is what makes it worth doing on a car worth keeping.