Oil cooler seal leak
Attaches to OM642 at engine level · Engine · carried by 4 variants across 4 chassis
Overview
Oil cooler seal leak is a common fault recorded against OM642 at engine level, typically from 150–280k km. It shows up as oil weeping down the back of the block, burning smell, oil in the valley beneath the intake. Where it's documented, the repair runs €900–€1,600 (intake off at a specialist, costs dated 2026-07), and it can be checked before you buy. 4 variants across 4 chassis in this database inherit it.
What happens
Symptom. Oil weeping down the back of the block, burning smell, oil in the valley beneath the intake.
Cause. The oil cooler sits in the vee under the intake manifold and its seals harden with age. Access requires the intake off, so labour dominates the bill.
Sources. specialist reports
How to check it
Static checks
Look down the back of the engine with a torch for wet oil and fresh cleaning. A suspiciously spotless engine bay on a 200,000 km V6 deserves a question.
Engine off, ideally on a lift.
Every variant that carries this
| Variant | Chassis | Body | Years | Risk | Good buy | Cost as % of good buy |
|---|---|---|---|---|---|---|
| C 320 CDI OM642 | W204 | sedan | 2007–2011 | R3 | €6,600 | 19% |
| C 320 CDI OM642 | S204 | wagon | 2008–2011 | R3 | €6,950 | 18% |
| E 350 CDI OM642 | W212 | sedan | 2009–2016 | R3 | €8,750 | 14% |
| E 350 CDI OM642 | S212 | wagon | 2009–2016 | R3 | €9,200 | 14% |
The last column is the point. The same repair is an inconvenience on one variant and a reason to scrap the car on another. A failure costing a quarter of the vehicle's value changes the purchase decision regardless of how rare it is.