The Mercedes Benz 601 diesel motor, technically referred to as the OM-601, while not the most exciting engine, was a revolutionary powerplant that paved the way for later diesel engines. The four-cylinder OM601 is noted for its incredible durability when maintained properly. Many owners of Mercedes Benzes with this motor have seen the engines last 300,000 to 400,000 miles or more. The engine was introduced in 1983 and powered the 190D sedan in 2.0-litre (European) and 2.2-litre (U.S.) versions.
The OM-601 is the smallest member of the OM-60X family of Mercedes engines and utilised a cast iron block with an aluminium head and featured a double overhead camshaft arrangement. To provide added under-hood clearance, the cylinders are canted 15-degrees to the side rather than arranged vertically.
Thanks to the aluminium head, the motor also weighed some 45.4kg less than the OM-61X that it replaced. The OM-601 produced 72-bhp at 4,200rpm and 96ft/lbs of torque at 2,800rpm. A duplex chain that runs off of the crankshaft drives the camshafts and fuel injection pump. There is a separate chain also on the crankshaft that drives the oil pump.
One of the notable features of the OM-601 is the fuel injection, which utilised a pre-chamber design that stayed in production until it was finally replaced by CDI rail-injection. The fuel injection pump was a Bosch PES-4M.
In its day, the motor returned quite impressive fuel economy figures that still look good today. M201 chassis cars that used the engine returned about 30+ mpg city and 45+ mpg freeway in the 2.0-litre version. The 2.2-litre was even more impressive, and could average 36mpg in the city and 55mpg on the freeway.
Along with regular oil changes, like all diesel motors, it is recommended that the engines be purged once a year and the glow plugs need replacement every few years. Every 150,000 miles the fuel return lines need replacement. Though the serpentine belt rarely breaks, it is important to monitor its condition and replace if damaged, since a broken belt can cause the motor to overheat.
While the OM-601 has a legendary reputation for reliability, there can be a few issues if the engines are not maintained properly. Due to the use of an aluminium head on a cast iron block, blown headgaskets often result in a warped head. Therefore, diligent replacement of the headgasket is recommended. The timing chain also needs to be replaced at the recommended service intervals.
The fuel lift pump for the fuel injection pump is oiled by a connection to the engine's oil supply, and the seal between the two is also prone to leaking. Though replacing the seal is time-consuming and must be done precisely and correctly, it is possible for an accomplished home mechanic. Fortunately, the OM-601's use of hydraulic lifters means that the there is no need for valve adjustments for the life of the motor.
For emissions reasons, California cars had an EGR valve to recirculate the exhaust gases. If not functioning correctly, these can cause driveability issues.
For colder environments, the engine features a block heater with an external cord that can be plugged in externally. This means that on cold mornings the block can already be heated, provided heat for the occupants as soon as the car is started.