The brief
Mr Kenny's E90 had been drinking oil for a long time, and his previous workshop had told him an engine top overhaul was the only solution, a big job. He came to us for advice and a quote before committing, which was worth doing. Oil that disappears with no leak on the ground is being burnt, and on these engines the usual cause is the valve stem seals, the little seals at the top of each valve stem that keep all but a film of oil off the stem. As that rubber hardens with age, oil runs down into the cylinders and is burnt with the fuel, so the level drops. Replacing the valve stem seals fixes it, and that's a much smaller job than a top overhaul, so a proper diagnosis is what tells you which you actually need.
The diagnosis
The checks pointed clearly at oil burning rather than a leak, the hallmark of worn valve stem seals, and with the engine opened up the seals were hardened, exactly the consumption Mr Kenny had been living with. The engine itself was sound, no top overhaul needed. That's a valve stem seal replacement with the timing reset, a small fraction of an engine top overhaul, rather than the big job he'd been quoted.
The work
The valve cover came off, the hardened valve stem seals carefully extracted with the correct special tools, and new genuine BMW-spec seals fitted on every valve. Everything was reassembled, the gaskets and seals renewed where disturbed, and the timing set correctly to spec. The engine was run, the oil level checked, and the consumption confirmed stopped. A road test confirmed a clean start with no smoke, smooth running, the oil level holding, and no warning lights.
The outcome
No more oil disappearing, the level holding between services, no blue smoke, smooth running, and no warning lights, all for a small fraction of a top overhaul. As Mr Kenny put it: "I had been stressed by the high engine oil consumption for a long time. My previous workshop advised that engine top overhaul was the only solution to the issue." The E90 went home with the consumption fixed at the source and a lot of money saved. A proper diagnosis is what made the difference here, because the gap between a set of valve seals and a top overhaul is enormous.
