Used Mercedes-Benz S420

What to know before buying: Mercedes-Benz S420

From 1 forum thread and 2 press tests · updated 12/10/2026

What the reviews say

• The S 420 CDI V8 delivers a very strong surge of power, but also noticeable turbo lag and fading acceleration during shifts.[1]one source
• Forum users report about 10 L/100 km in town and 8–9 L/100 km at 130 km/h for the V8 diesel; these are owner observations, not a standardised test.[1]one source
• One owner reported no problems with his 4.0 CDI and stressed that treatment and maintenance materially affect the outcome.[1]one source
• Opinions on the V8 diesel conflict: some consider it an expensive risk, while others caution that isolated failures do not prove the entire engine unreliable.[1]one source

Typical faults

• For W220/W221 V8 diesels, the forum flags a risk of costly turbocharger failures; it gives no typical failure mileage.[1]one source

  V8 CDI

• The same source also flags costly injector failures on W220/W221 V8 diesels, but provides no year or mileage range.[1]one source

  V8 CDI

Which engine and version to take

• Choose the 4.0 CDI only with evidence of careful use: an owner advises warming and cooling the turbos and avoiding high revs for the first 20–25 km.[1]one source

What to avoid

• Avoid a V8 CDI with unclear maintenance and usage history: the forum specifically highlights the risk of expensive turbo and injector failures.[1]one source

What to check at the inspection

• During a pre-purchase inspection, pay particular attention to the turbochargers and injectors, as the forum describes failures of both as costly.[1]one source
• Ask how the car was warmed and cooled and whether it was revved hard when cold; an owner links these habits to diesel longevity.[1]one source
• When researching faults, match the exact generation, engine and year: one forum explicitly requires these details, while the S-Class question archive spans many different years and engines.[2][3]

Verdict

Sources

1. [1]motor-talk.de — Motorschaden S420CDI und S450CDI - Mercedes · forum
2. [2]foorum.clubmb.ee — S-klass - Mercedes-Benz Eesti Klubi Foorum · press
3. [3]drom.ru — Вопросы по Mercedes-Benz S-Class · press

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