Mercedes-Benz OM603 engine

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The OM603 engine was a straight-6 Diesel automobile engine from Mercedes-Benz used from 1984 through 1999. The 603 saw limited use in the W124, W126 and W140 model vehicles.

Mercedes-Benz OM603 Diesel Engine
Production1986 to 1997
ConfigurationInline-six engine
Displacement3.0 L (2996 cc)
3.5 L (3449 cc)
Cylinder bore87 mm / 3.43 inches
Piston stroke84 mm / 3.31 inches
ValvetrainOHC / 2 Valves per Cylinder
Compression ratio22.0:1
TurbochargerNo (.912), Yes (.96x, .97x, KKK K24)
Fuel systemFuel injection
Fuel typeDiesel
Power output109 - 150 hp (81 - 111 kW)
Torque output185 Nm - 310 Nm
Dry weight217 kg

The 603.96 engine has a capacity of 2,996 cc (182.8 cu in) and was developed from the earlier 5 cylinder OM617. It produced 143 hp at 4600 rpm (euro market without catalytic converter produced 148hp) and 195 at 2400 rpm with a compression ratio of 22.0:1. Versions 603.96x and 603.97x are turbocharged. Only turbocharged models of the 603 series were available to the U.S. market. The single camshaft and injection pump are driven by duplex chain from the crankshaft. A separate single row chain drives the oil pump. The camshaft operated the valves via hydraulic bucket tappets; valve clearance adjustment is automatic.

Fuel is injected into a pre-combustion chamber. A Bosch M in-line injection pump is used, with a mechanical governor and vacuum-operated stop control. The pump is lubricated by a connection to the engine oil circulation and the fuel lift pump is mounted on the side of the injection pump. Preheating is by glow plugs with automatic control of preheating time.

The 603 engine had a diesel particulate filter, or trap oxidizer, in the US market. As these were mounted at the cylinder head (modern traps are mounted further away), heat from these trap oxidizers caused failure of the aluminum cylinder heads on the first generation of 603-engined vehicles; debris from the traps could also damage the turbocharger. This first version was sold in the US from 1986 to 1987. Daimler-Benz removed these traps for free, and if the turbocharger had been determined to be damaged it was also replaced. Even without the heat from the trap oxidizers, the original #14 mold cylinder heads were weak and if overheated could crack as with any overheated engine. In general, the later model #18 or #22 mold cylinder heads are considered to be the definitive cure for cracked heads.[citation needed]

In 1990 the 350SD/SDL debuted, using a larger-displacement 3496cc OM603.97 engine that had more torque and a lower top RPM. The engine lived on in the W140 chassis after the W126 production ended, as the 300SD or S350, with a larger yet turbocharger and thus more power and torque. By the time of the 3.5L engine, the cylinder head issues of early 3.0L engine (US 1986-1987) had been corrected. However, in the 3.5L there exists a different situation that appeared on some engines; eventual head gasket erosion, and thus passage of oil into the #1 cylinder. As the 3.0L engine uses the same head oil passage design, yet does not appear to exhibit the problem - it might be that the larger bore in the 3.5 engine, the higher pressures, and resulting smaller head gasket surface area could conspire to cause a gasket erosion issue.

Versions of OM603 Mercedes 6-cylinder diesel engineEdit

Model indication Year Engine no OM603... Power in kW (hp) Torque in Nm
OM (6-cylinder diesel)
W124 300 D 04/1985 -> 06/1993 .912 81 (109) @ 4600 rpm (<'89) or 84 (113) @ 4600 rpm (>'89) 185 @ 2800 rpm (<'89) or 191 @ 2800 - 3050 rpm
W124 300D Turbo 01/1987 -> 03/1996 .960 & .963 (4Matic) 106 (143) @ 4600 rpm (<'88) or 108 (147) @ 4600 rpm (>'88) 267 @ 2400 rpm (<'88) or 273 @ 2400 rpm (>'88)
W124 300TD Turbo 1987 .960 106 (143) @ 4600 rpm (<'88) or 108 (147) @ 4600 rpm (>'88) 267 @ 2400 rpm (<'88) or 273 @ 2400 rpm (>'88)
W126 300SDL 02/1985 -> 09/1987 .961 110 (148) @ 4600 rpm 273 @ 2400 rpm
W126 350SD/SDL 06/1990 -> 08/1991 .97x 100 (136) @ 4000 rpm 310 @ 2000 rpm
W140 300SD / S350 09/1991 -> 08/1996 .97x 111 (150) @ 4000 rpm 310 @ 2000 rpm