On paper they look like twins. Both are 3.2-litre inline-six common-rail diesels. Both came out of Stuttgart back to back — the OM648 took over from the OM613 in 2002. Both made around 200 horsepower in big, comfortable Mercedes saloons. And in our database they now score exactly the same: 84/100, BUY.
So the question is no longer "which one is the good one?" It's "what is actually different, and which suits the car you're looking at?"
Quick answer: Both the OM613 (84/100, BUY) and the OM648 (84/100, BUY) are sound buys. Their weak spots differ: the OM613's record is all about the injectors — leaking copper seals and the six common-rail injectors themselves. The OM648 shares the seal problem but adds EGR fouling and glow plugs instead of injector failure. Pick by car, year and condition, and check the injector wells on either.
OM613 — 84/100 (BUY)
The OM613 was the first-generation 3.2 CDI six (1999–2003, 197 hp, 470 Nm). Engine guides quote around 400,000 km with proper servicing. Its documented problems all sit in the common-rail injection:
| Problem | Severity | Repair cost |
|---|---|---|
| Injector failure (expensive I6) | High | No sourced figure |
| Injector copper seal leak ("black death") | Moderate | €47–281 |
The seal leak is the classic "black death": the copper washers under the injectors burn through, combustion gas and diesel escape, and the mess bakes into carbon in the injector wells. Caught early it's a cheap job. Left alone, an injector can seize in the head, and snapped bolts can ruin the cylinder head. Separately, the injectors themselves wear with age; six of them make a full set expensive, but no source gives a price, so we don't quote one.
One note on the score: on our rubric the OM613 would land slightly higher, but any score above 84 needs at least five independent sources including a specialist. The OM613 has four, so it is capped at 84.
Found in: Mercedes E-Class (W210 E 320 CDI, 1999–2002), S-Class (W220 S 320 CDI, from 1999).
OM648 — 84/100 (BUY)
The OM648 (2002–2006, 204 hp) is the follow-up to the same recipe. Its record has no high-severity fault, but it carries two maintenance items:
| Problem | Severity | Repair cost |
|---|---|---|
| EGR valve fouling (city use) | Moderate | €300–700 |
| Injector seal leaks (black death) and glow plugs | Minor | €150–400 |
The same copper-seal "black death" shows up here, and the deposit can coke the injectors in place, which makes later removal harder. Glow plugs fail and can seize too. The EGR valve and cooler foul with soot and the intake flaps can jam with carbon — worse with city-only driving.
Found in: Mercedes E-Class (W211 E 320 CDI), S-Class (W220 S 320 CDI, 2002–2005).
The evidence, side by side
| OM613 | OM648 | |
|---|---|---|
| Displacement | 3.2L I6 | 3.2L I6 |
| Years | 1999–2003 | 2002–2006 |
| Power | 197 hp | 204 hp |
| Score | 84/100 | 84/100 |
| Verdict | BUY | BUY |
| Worst documented fault | Injector failure (High) | EGR fouling (Moderate, €300–700) |
| Injector seal leak | Moderate, €47–281 | Minor (with glow plugs), €150–400 |
How to choose
With the scores level, choose on the car in front of you:
- The car decides the engine. A W210 E 320 CDI means OM613; a W211 E 320 CDI from the OM648 years means OM648. The W220 S 320 CDI had both — the 197 hp OM613 from 1999, the 204 hp OM648 from 2002 — so check the year and the power figure on the papers.
- On either engine, look at the injector wells. Black, tar-like residue around the injectors under the engine cover, a "chuffing" noise or a diesel/exhaust smell in the cabin all point to leaking seals. Fix it before the injectors seize.
- On an OM613, ask about the injectors themselves. Rough idle, misfires, smoke and hard cold starts are the warning signs of worn injectors — the one high-severity item in this comparison.
- On an OM648, ask how the car was used. A city-only history raises the odds of a sooted EGR valve and jammed intake flaps; also check the glow plugs on a cold start.
Neither is the "safe" one and neither is the gamble. Both are big, long-lived Mercedes diesel sixes; the better buy is simply the better-kept car.
For the modern equivalent of this "which generation?" question, see how the four-cylinder diesels evolved in our OM651 vs OM654 comparison.
Scores are calculated from documented issues, repair costs, and failure patterns. Reviewed by the EngineScope editorial team. Methodology →