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Your Oil Pump worn out? » Read more about common malfunctions • Repair • Replacement manual
Power behind the lubricant: the oil pump
The oil pump is the engine component responsible for building up the oil pressure and the distribution of the lubricant in the engine. It is flanged onto the engine and is directly driven by it.
Oil pump: construction
The oil pump functions according to a vane pump principle. In a round casing sits a rotor, stirring the oil with vanes supported by springs. As the rotor is installed slightly at an angle to its centre, the pump works eccentrically. This makes the oil pump very efficient and is very suitable for development of a sufficient amount of pressure. Alternatively to the vane pump, the simpler gear pump, crescent pump or rotor pump are used as well.
Oil pump: location
The oil pump is directly flanged onto the engine and receives its torque directly from the crankshaft. The transmission occurs via a gearwheel or a separate drive chain. A belt drive is only rarely used for the oil pump. A slipping belt would cause the pump to cease function, which would be fatal for the engine. It is a complex component, consisting of a die-cast casing, screws, gasket and pumping unit. It is always replaced in its entirety. The entire amount of oil in the engine is pumped through the tubes 4 to 6 six times per minute. This performance rate is required for sufficient lubrication of all moving parts in an engine.
Life span and defects of an oil pump
The oil pump easily reaches a life span of 150.000 km or more. When it fails, this is usually the result of faulty maintenance. Polluted or very old or too thin oil can damage the pump. There is an oil check light on the dashboard, connected to the oil pressure switch. When the oil pressure falls below the minimum level, the oil pressure switch is activated. Cause for a pressure loss in the lubricating system is either leakage or a defective oil pump. If no excessive amounts of oil are leaking from the engine, the oil pump is probably damaged. Further symptoms can be a grinding noise, rattling or a consistently minimal oil pressure.
Manually measuring the oil pressure in a car
An oil pressure check light can indicate a sensor error, and therefore the oil pressure should always be checked manually before disassembling the engine. Measuring equipment costs ca. 50 EUR (± £ 45). In order to check the oil pressure, the pressure switch is removed and on its opening on the engine the manometer is screwed on. You need the correct pressure values for the car. They can vary greatly depending on engine temperature and rotation speed. In a Mercedes W124 the pressure values can lie between 0,6 and 4,7 bar. Making a measuring list is a lot of work, but it will keep you on the safe side and you will know exactly if the oil pump is still functional.
Replacing an oil pump
The oil pump sits at the bottom of the engine in the immediate vicinity of the oil sump. If the car has chain drive, it must be disassembled. Subsequently all bolts are removed and the pump is pulled to the front. The new pump is now installed with a new gasket. Often, additional components need to be removed as well. The oil pump can only be replaced from underneath the car which requires jacking it up. For jacking up, only suitable jack stands should be used. They are available at little cost in the component trade. Inadequate jacking up is very dangerous and can warp the car chassis. A new oil pump automatically implies oil and oil filter change as well as replacing the oil pressure switch. If pressure changes persist, the riser pipe of the oil sump should be checked. Although this hardly ever happens, it can be clogged. If the engine is excessively polluted, an thorough internal engine washing should precede the installation of a new oil pump. This requires several drainages of the rinsing oil. Not until the engine is completely free from deposits, the new oil pump can be installed.
Oil pump costs
The price of an oil pump starts at ca. 30 EUR (± £27). It depends for a great deal on the car type, how expensive it can be. As this is a complex special component, the choice of manufacturers is limited. Nevertheless, branded quality should always be observed.