Mercedes-Benz M104
inline-6 · naturally aspirated · petrol · 1989–present
Also known as: m104, m103, 3.2 straight-six mercedes, 2.8 straight-six mercedes, m104 e32
Mercedes' 2.8 and 3.2 petrol straight-six — the M104 — in the W124, W140 and W202, and licence-built into the SsangYong Rexton, Kyron and Rodius.
Its SsangYong life is the reason it is worth a page here. Long after Mercedes stopped fitting it, SsangYong went on building it, so a 2000s Korean SUV can carry a 1990s German straight-six — and Mercedes parts and Mercedes diagnostic material apply directly, which almost nothing else about those vehicles does.
⚑ Its notorious fault is the wiring harness. Mercedes used biodegradable insulation on engines of this era; it becomes brittle and crumbles off the loom, producing shorts, phantom sensor faults and misfires that chase from cylinder to cylinder. A harness in that condition cannot be repaired by chasing individual faults — it is replaced, and diagnosing around it wastes days.
The head gasket and the timing chain guides are the other known items on high-mileage engines, and the chain rattle on a cold start is the usual warning.
Otherwise it is a durable, unstressed engine, which is exactly why it stayed in production for so long after the cars it was designed for.
Cars fitted with this engine
2 generations, across 1 make. 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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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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