"Is the S Serisi S250 reliable, and what should you check?"
The most commonly reported issue when buying a used Mercedes-Benz S-Class S250 2011 (221 / Facelift): cracks in the plastic intake manifold. Also, oil leaks from the timing chain tensioner/hydraulic chain tensioner are frequently reported.
Engine: OM651
OM651.961 · diesel · S250 · Used in this car from 2011-2013
Strengths
Decent lifespan with proper maintenance
Modest fuel consumption for such power
Watch-outs
Finicky Delphi fuel system
Frequent bearing shell rotation
Low timing chain tensioner lifespan
Known engine issues
Fuel systemUntil 2011, main versions used Delphi fuel system with piezo injectors prone to leaks, often causing hydraulic lock and piston burn-through. A recall was even issued to replace them with simpler electromagnetic ones. Engine modifications with Bosch fuel system have no reliability issues.
Bearing shell rotationMany owners of vehicles with this diesel have encountered bearing shell rotation. The cause is dilution of overheated oil due to clogged heat exchanger or oil pressure drop from variable displacement oil pump failure. The engine also lacks a standard oil pressure sensor, but one can be installed.
Timing chain hydraulic tensionerThe combined timing drive consists of a roller chain and several gears. The chain can last up to 300,000 km, but its hydraulic tensioner often fails much earlier, and replacing it is quite labor-intensive and expensive.
Listed from most frequently reported, each with its source.
Cracks in the plastic intake manifold
Often reported
The plastic intake manifold on the OM651 engine can develop cracks or air leaks over time, causing power loss, rough idle, and the check engine light to come on.
Engine Bay
Oil leaks from the timing chain tensioner/hydraulic chain tensioner
Often reported
On some OM651 engines, oil leaks from the timing chain tensioner/hydraulic tensioner have been reported. The leak can impair tensioner function and accelerate wear of the chain and sprockets. If not addressed in time, noises may be heard from the cover.
Engine Internal
Oil-water heat exchanger blockage and cooling efficiency loss
Often reported
The oil/water heat exchanger on the OM651 engine is reported to experience blockage or efficiency loss, reducing oil cooling and leading to oil degradation and engine wear.
Engine Internal
EGR/DPF blockage and problematic regenerations
Often reported
The OM651 engine in the S 250 CDI can experience EGR valve and DPF blockage, especially during city or short-distance driving. Symptoms include performance loss, frequent regenerations, and increased emissions.
Exhaust Emissions
Injector failures (OM651)
Often reported
The 2.1 OM651 engine in the S 250 CDI has documented injector issues, particularly with piezo injectors in early versions.
Fuel System
Mercedes-Benz S Serisi S250 technical specs
Mercedes-Benz S Serisi S250 (2011): boot 560 L; fuel use 5,8 l/100 km (urban 7,1 l/100 km · extra-urban 5 l/100 km); 0–100 in 8.2 s.
Boot capacity
560 L
Fuel consumption
5,8 l/100 km (urban 7,1 l/100 km · extra-urban 5 l/100 km)
What should I look for when buying a Mercedes-Benz S-Class S250?+
When buying a 2011 S250, check the service history, test drive, and look for engine/transmission warnings. The most frequently reported issues: cracks in the plastic intake manifold; oil leaks from the timing chain tensioner/hydraulic chain tensioner; oil-water heat exchanger blockage and cooling efficiency loss.
What are the chronic problems of the Mercedes-Benz S-Class S250?+
The most frequently reported issues: cracks in the plastic intake manifold; oil leaks from the timing chain tensioner/hydraulic chain tensioner; oil-water heat exchanger blockage and cooling efficiency loss.
Is the Mercedes-Benz S-Class S250 reliable?+
Instead of a simple yes/no, it is necessary to evaluate the proven pros and cons together. This page lists 5 verified findings.
How does Carbeak collect data?+
The cards on this page are derived from the Difetti fault database records; the source vehicle and target vehicle are verified for brand, fuel, engine, and generation compatibility. Topics with insufficient evidence are not shown.