134416-0720 ZEXEL 9 411 612 876 BOSCH COVER 9411612876 1344160720 6073121170

The lubrication system consists of a sump (oil pan), oil pump, oil cooler and oil filter. The engine contains an oil manifold and oil passages to direct lubricant to the various components.The oil pump draws lubricant from the sump and forces it through the oil cooler, oil filter, and then into the oil manifold. Oil flows through connecting passages to lubricate the engine components. A regulating valve in the pump body controls the maximum pressure of the oil from the pump. When the engine is started, the lubricating oil in the oil pan is cool (thick). This cool viscous oil does not flow immediately through the oil cooler and oil filter. This cool oil forces bypass valves, in the oil cooler and oil filter base, to open allowing an unrestricted oil to flow through the engine.As oil temperature increases, oil viscosity and pressure decrease and the oil filter bypass valve closes. Now, only filtered oil is delivered to the engine components. Oil temperature continues to increase and the oil cooler bypass valve closes. Oil now flows through the oil cooler and oil filter before reaching the engine components.A contaminated or restricted oil filter element will not prevent lubricating oil from being delivered to the engine components. The oil filter bypass valve will open, allowing oil to bypass the element.An oil manifold, cast into the cylinder block, directs lubricant to the main bearings, valve rocker arm shafts, camshaft journals, and the camshaft idler (drive) gears.Oil spray orifices in the cylinder block spray oil on the underside of the pistons. This cools the pistons and provides lubricant for the piston pins, cylinder walls and piston rings.The connecting rod bearings receive oil through drilled passages in the crankshaft between the main bearing journals and connecting rod journals.When the engine is warm and running at rated speed, the oil pressure gauge should register in the "operating range". A lower pressure reading is normal at idling speeds.Many engines are equipped with an auxiliary or remote mounted bypass filter system. This system must be connected so part of the oil continuously circulates through the bypass filter, from the crankcase lubricating oil pump. An orifice on the outlet or clean side of the filter restricts the flow of oil through the bypass filter so full oil pressure is available to all parts of the engine. Filtered oil from the bypass filter is returned to the crankcase sump. Because of the additional oil capacity, extended change intervals can be established. See Lubrication Chart. The Bypass filter should never be used in place of the factory installed full flow filter.