BMW M51 (U25TD / Y25DT)
2.5 L · inline-6 · turbocharged · diesel · 1991–present
Also known as: m51, m51d25, u25td, y25dt, x25dt, 2.5 tds, bmw 2.5 diesel
BMW's 2.5 diesel straight-six — the M51 — in the E34 and E36 and the Range Rover P38, and in the Opel Omega under the codes U25TD and Y25DT.
⚑ An Opel with a BMW engine is the fact this page exists for. Opel bought the M51 for the Omega B, and BMW material describes it while Opel material largely does not — an Omega owner searching Y25DT finds very little and searching M51 finds a decade of BMW and Land Rover experience.
It is an indirect-injection engine on the early cars and direct-injection on the later M51TU, and that division matters more than the shared displacement.
Its known items are the swirl flaps and the vacuum system. The flaps in the inlet manifold wear and can come loose; the vacuum pump and its lines age and produce a brake and turbo-actuator complaint together, which reads as two faults and is one.
The M57 that replaced it is common-rail and has its own page here; nothing about the two transfers.
Cars fitted with this engine
2 generations, across 2 makes. From the authored catalogue — an absent car means the catalogue has not reached it, not that the engine was never fitted.
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Posted about this engine
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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