The OM603 engine was a

straight-6 The straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine bal ...

Diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...

automobile engine from

Mercedes-Benz Mercedes-Benz (), commonly referred to as Mercedes and sometimes as Benz, is a German luxury and commercial vehicle automotive brand established in 1926. Mercedes-Benz AG (a Mercedes-Benz Group subsidiary established in 2019) is headquartere ...

used from 1984 through 1999. The 603 saw limited use in the

W124 The Mercedes-Benz W124 is a range of mid-size cars made by Daimler-Benz from 1984 to 1997. The range included numerous body configurations, and though collectively referred to as the W-124, official internal chassis designations varied by body st ...

W126 The Mercedes-Benz W126 is the company's internal designation for its second generation S-Class, manufactured in sedan/saloon (1979–1991) and coupé (1981–1990) models, succeeding the company's W116 range. Mercedes introduced the 2-door C1 ...

and W140 model vehicles. It is closely related to the

4 cylinder The engine configuration describes the fundamental operating principles by which internal combustion engines are categorized. Piston engines are often categorized by their cylinder layout, valves and camshafts. Wankel engines are often categorize ...

OM601 and the 5 cylinder OM602 engine families of the same era. The 603.96 engine has a capacity of and was a development of the reliable 5 cylinder OM617 engine. It produced 143 hp at 4600 rpm (euro market without catalytic converter produced 148hp) and 195 ft.lb 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. In general, the later model #17 or #22 mold cylinder heads are considered to be the definitive cure for cracked heads. 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 engine

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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 , - ,

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) , - ,

300TD Turbo , 1987 , .960 , 106 (143) @ 4600 rpm (<'88) or 108 (147) @ 4600 rpm (>'88) , 267 @ 2400 rpm (<'88) or 273 @ 2400 rpm (>'88) , - ,

300SDL , 02/1985 -> 09/1987 , .961 , 110 (148) @ 4600 rpm , 273 @ 2400 rpm , - ,

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 , - OM603 Diesel engines by model Straight-six engines