Oil pump

The oil pump, oil filter and oil cooler together form the lubrication circuit that protects bearing shells, camshafts, pistons, crankshaft, turbochargers and timing components. On MAN D08, D20, D26 and D38 engines and Mercedes OM 906, OM 457, OM 471 and OM 473 engines, pump designs, filter modules, cooler connections, seals and pressure control strategies differ considerably. Therefore, always identify these parts using the chassis number.

Oil pumps are generally gear pumps or gerotor pumps that draw engine oil from the oil sump and deliver it to the main oil gallery at regulated pressure. From this gallery, the oil flows directly to the vital moving engine components that require pressurised lubrication. Through drillings in the engine block, the oil first flows to the crankshaft main bearings and then through internal channels in the crankshaft to the connecting rod bearings. One or more riser passages run from the gallery to the cylinder head, allowing the oil to lubricate the camshaft bearings, cam lobes, rocker arms and hydraulic valve lifters. On many truck engines, oil jets are mounted directly on the oil gallery. They spray a constant jet of oil onto the underside of the pistons to cool them while simultaneously lubricating the cylinder walls. The turbo bearings are lubricated via a branch line from the gallery. After the oil has been forced through all these components and has performed its lubricating and cooling function, it loses pressure. It then drips back into the oil sump through return passages under the force of gravity. Operating pressure is determined by engine speed, engine oil viscosity, oil temperature, bearing clearance and the operation of the pressure relief valve. Oil pressure that is too low when the engine is warm is a critical fault condition: the lubricating film on crankshaft bearings, connecting rod bearings, camshaft bearings and turbocharger bearings becomes too thin, resulting in accelerated metal-to-metal wear.

Typical causes include worn pump gears or rotor surfaces, a defective pressure relief valve, a cracked oil pickup pipe, a hardened O-ring on the suction side, a contaminated oil pickup screen or excessive clearance in plain bearings. First measure the actual oil pressure using a calibrated pressure gauge at the designated measuring point. Compare cold and warm pressure values at idle speed and the specified increased engine speed. In case of deviations, also check the viscosity, oil level, presence of fuel dilution and metal particles in the drained engine oil.

Oil filters remove soot, wear particles, seal residues and other contaminants from the engine oil. Depending on the engine family, these are spin-on filters or filter elements in an integrated oil filter module. A filter element must have the correct filtration rating, sealing diameter, height and bypass or pressure relief valve specification. An incorrect filter may leak internally, restrict oil flow or open the unfiltered bypass too early.

At every service, check the oil filter housing for damaged threads, flatness of the sealing surface and any old sealing rings left behind. Cut open a removed filter element if engine damage is suspected: aluminium particles may indicate piston damage, while copper-coloured or magnetic steel particles may point to plain bearings or gear and chain drives respectively. Excessively long oil change intervals, incorrect engine oil or internal wear cause oil filters to become clogged. When an oil filter becomes completely clogged, the integrated bypass valve opens. Although this prevents the engine from running without oil, a clogged oil filter has serious and destructive consequences for the engine. Because the oil flows around the filter element via the bypass, it is no longer cleaned. Dirt, small metal particles, carbon deposits and soot therefore remain in the engine oil and are pumped through the engine repeatedly. The circulating contamination acts like sandpaper and causes damage to vital engine components.

Oil coolers are usually plate heat exchangers in which engine oil transfers heat to the engine coolant. They limit oil temperature under high load, during prolonged uphill driving and during intensive use of trucks, buses and vans. An internally leaking oil cooler causes oil in the expansion tank or coolant in the engine oil. This contamination affects viscosity and corrosion protection properties and can cause bearing damage.

Perform a pressure test on the cooling system and isolate the oil cooler if the design permits. Also check for external leaks at coolant hoses, banjo bolts, connection flanges and O-rings. In the event of confirmed internal leakage, replace not only the oil cooler, but also flush the cooling system and clean the filter housing, oil passages and expansion tank according to the prescribed procedure. Based on the chassis number, Braem can help identify the correct oil pump, oil filter module or oil cooler, thereby limiting unnecessary downtime.