Mercedes CDI Black Death


Mercedes B Class 180 CDI


17 September 2019



Mercedes CDI Black Death

Another CDI engined Mercedes with the 'Black Death' in our workshop today.

What does the term “Black Death” mean on Mercedes vehicles?

Due in part to poor design, the injector seals on Mercedes diesel engines can leak, which means uncombusted diesel fuel and exhaust gases can leak these gasses are pushed back past the injector seal and up the injector shaft. This happens during the compression and exhaust strokes of the engine. The result of this leakage means the space between the rocker cover and the plastic lid can becomes full of a sticky carbon like substance, which will get worse if left untreated. It will ultimately lead to complete breakdown.

What causes the injector seals to fail.

When we look at the root cause of the Mercedes 'Black Death' we can attribute it to 2 main factors; the bio element of diesel fuel, and extended service intervals. 

The bio fuel in the diesel fuel you have to purchase at the pumps leaves microscopic deposits within the fuel injectors, over time these build up and eventually cause a partial blockage of the fuel injector. This blockage affects the spray pattern of the fuel injector which in turn causes an increase of combustion pressure during detonation of the fuel. This increased combustion pressure works against the the tip of the fuel injector and lifts the injector away from its seat, thus breaking the seal between the fuel injector and the sealing washer.

This is an ever worsening situation that eventually leads to the injector seals failing and the leakage occurring that has become affectionately know as 'Black Death'.

Properly servicing your Mercedes along with the use of a diesel fuel treatment that will remove the bio deposits from the fuel injectors will help to minimise the risk of your Mercedes suffering a similar fate. That's why we use a special diesel fuel treatment from Forte on all our customers vehicles when we service them. This treatment not only removes deposits from your fuel injectors, it also improves your fuel efficiency and makes your engine run smoother.


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01420 479477


Unit 13 Broxhead Trading Est,

Broxhead Farm Rd,



GU35 0JX

Company Number 08710977

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