Mercedes OM651 vs OM654: Used Diesel Buying Guide
The Mercedes OM651 and OM654 can both be good used diesels, but they suit different buying situations. The OM651 is older and widely understood. The OM654 is newer, efficient, and usually the stronger modern choice when emissions data is clean.
For the full side-by-side page, open Mercedes OM651 vs OM654.
OM651: older, proven, but condition-sensitive
The OM651 can handle mileage well, but age matters now. Injector issues, timing wear on neglected cars, cooling behavior, battery voltage, and diesel emissions faults all need proper checks.
Before buying, verify:
- Mercedes-capable full module scan
- Injector corrections and smooth cold running
- DPF, EGR, NOx, and AdBlue status
- Battery and charging-system health
- Oil, fuel filter, gearbox, and brake-fluid history
OM654: newer, cleaner, still not simple
The OM654 is usually the better newer engine, but do not confuse newer with low risk. Modern diesel emissions systems can be expensive when faults are cleared instead of fixed.
Look for NOx sensor history, AdBlue countdown evidence, DPF regeneration data, coolant behavior, and complete service invoices.
On modern Mercedes diesels, a calm test drive is not enough. You need module-level data before trusting the car.
Which should you buy?
Choose the OM654 when the scan is clean and the car has proper service proof. Choose the OM651 when the purchase price is sensible and the records are unusually strong. Avoid either engine if warning lights, AdBlue faults, or battery issues are being explained away.