Mercedes OM603 6-cylinder engines of 3.0 and 3.5 liters were produced from 1984 to 1997 and were installed on a number of popular models of the German concern, such as W124, W126 and W140. Three modifications of this diesel engine were offered, atmospheric and two turbocharged.
The diesel R6-family includes: OM603, OM606, OM613, OM648, OM656.
Specifications
| Production years | 1984-1997 |
| Displacement, cc | 2996 (OM 603 D 30 or 300D, OM 603 D 30 A or 300TD) 3449 (OM 603 D 35 A or 350SD) |
| Fuel system | prechamber |
| Power output, hp | 109 – 113 (D30) 143 – 150 (D30A) 136 – 150 (D35A) |
| Torque output, Nm | 185 – 191 (D30) 267 – 273 (D30A) 305 – 310 (D35A) |
| Cylinder block | cast iron R6 |
| Block head | aluminum 12v |
| Cylinder bore, mm | 87 (D30, D30A) 92.4 (D35A) |
| Piston stroke, mm | 84 (D30, D30A) 89 (D35A) |
| Compression ratio | 22.0 |
| Features | no |
| Hydraulic lifters | yes |
| Timing drive | chain |
| Phase regulator | no |
| Turbocharging | no (D30) KKK K24 (D30A, D35A) |
| Recommended engine oil | 5W-40 |
| Engine oil capacity, liter | 7.5 |
| Fuel type | diesel |
| Euro standards | EURO 1 |
| Fuel consumption, L/100 km (for Mercedes E 300 TD 1994) — city — highway — combined |
9.3 6.2 7.9 |
| Engine lifespan, km | ~450 000 |
| Weight, kg | 235 |
The engine was installed on:
- Mercedes E-Class W124 in 1984 – 1995;
- Mercedes G-Class W463 in 1990 – 1997;
- Mercedes S-Class W126 in 1985 – 1991; S-Class W140 in 1992 – 1996.
Disadvantages of the OM603 engine
- This diesel unit is very vibroloaded, which affects the resource of its pillows;
- The timing chain runs no more than 250,000 km, and if it breaks, you will have to change the block head;
- From cheap or old antifreeze or water in general, the cylinder head gasket often breaks through;
- Hydraulic lifters are afraid of low-quality oil and can knock even up to 80,000 km;
- The rest of the motor problems are usually associated with the vacuum injection pump control system.
Modifications OM603
| Modifications | Power, kW (hp) | Torque output, Nm |
| OM603.912 | 81 (109) at 4600 rpm | 191 at 2800 – 3050 rpm |
| 84 (113) at 4600 rpm | 185 at 2800 rpm | |
| OM603.960 and OM603.963 (4Matic) | 106 (143) at 4600 rpm | 267 at 2400 rpm |
| 108 (147) at 4600 rpm | 273 at 2400 rpm | |
| OM603.960 | 106 (143) at 4600 rpm | 267 at 2400 rpm |
| 108 (147) at 4600 rpm | 273 at 2400 rpm | |
| OM603.961 | 110 (148) at 4600 rpm | 273 at 2400 rpm |
| OM603.97x | 100 (136) at 4000 rpm | 310 at 2000 rpm |
| OM603.97x | 111 (150) at 4000 rpm | 310 at 2000 rpm |
The 603rd series are 6-cylinder engines packed in steel blocks with an aluminum cylinder head, equipped with hydraulic pushers, a reliable injection pump and other progressive improvements. When developing OM 603, the engineers paid special attention to the control over emissions, these were improved models that allow to reduce the smoke of the exhaust by 40%.
The camshaft and injection pump are driven by a duplex chain from the crankshaft. A separate single-row chain drives the oil pump. The camshaft acts on the valves using hydraulic tappets. The valve is automatically adjusted.
Fuel is injected into the pre-combustion chamber. The Bosch M injection pump with mechanical control and vacuum control is lubricated by connection to the engine oil circulation, the fuel lift pump is installed on the side of the injection pump. The preheating is carried out automatically by the glow plugs.
Due to the tightening of emission regulations in the US market, a diesel particulate filter has been created. Since they were installed on the cylinder head (modern ones are installed further), the heat from them caused the failure of the aluminum cylinder heads, and debris from the filters could damage the turbocharger.
Another typical malfunction of the Mercedes OM603 engine is strong vibrations. This causes the crankcase screws and bolts to loosen. The latter enter the oil pump or clog the channels, which ultimately leads to oil starvation, bearing damage and broken block rods.
