The brief
The Passat had a low-oil warning lighting up between services, an oil stain on the floor where it parked, and the dipstick was dropping faster than the owner expected. Two related faults, both pointing at the bottom of the engine rather than a top-end leak.
The sump is the pan at the bottom of the engine that holds the oil, sealed to the block with a gasket. When that gasket hardens and the seal lets go, oil weeps out and drips onto the floor, which is the stain and the dropping level. And down there too is the oil level sensor that feeds the dash, so a sensor playing up adds a false low-oil warning to the mix. The job was to sort both.
The diagnosis
The underbody inspection found oil weeping at the sump gasket where it meets the block, with the bolts visibly tightened by an earlier owner attempt to chase it, which never works on a hardened gasket. And the scan tool threw a fault on the oil level sensor reading inconsistent.
So it was two things: the sump gasket gone, and the sensor on its way out. Both due for replacement, and since the sump has to come off for the gasket anyway, the sensor gets done at the same time.
The work
The engine oil was drained into a clean catch, the sump came off, and the old gasket material was cleaned off the mating faces of both the sump and the block. A new VAG-spec gasket went on, the oil level sensor was replaced with a fresh seal, and the sump bolts were torqued to spec in the correct sequence.
Then the engine was refilled with fresh oil to level, the sensor fault cleared, run warm, and the underside checked dry before a test cycle.
The outcome
No stain on the floor over the test cycle, no low-oil warning, and the sensor reading consistent on the scan tool.
The Passat went home with the leak sealed and the dash telling the truth again. Doing the gasket and the sensor together, while the sump was off, means both halves of the problem are closed off in one visit, rather than a leak fixed now and a sensor warning still nagging.
