Engine Internal Lubrication
Every engine needs oil, the right kind of oil, for not only lubrication, but to help dissipate internal heat also. For brevity in this explanation, we will assume a generic internal combustion, automotive engine. In generalities, it could be a Ford, Chevrolet, Mercedes or any other typical automobile, or truck for that matter. We will assume that it a gasoline powered engine.
There are actually very few parts to the engine's internal lubrication system. There is an oil pan, where the oil is stored and where the oil flows by gravity, since it is the lowest point in the engine, when it trickles down the internal parts of the engine. There is an oil pump, which, through a pickup pipe, pumps the oil under pressure, to lift it against gravity to the upper parts of the engine, and all of the other internal moving parts. There is the oil filter; the first place the oil goes after leaving the pump. The filter removes any grit, dirt and impurities from the oil itself and captures them inside the filter. Periodically, the filter is removed and replaced, discarding the impurities. In order to create the pressure to move the oil, the oil pump is connected by gears to the engines internal moving main components, either directly or indirectly to the crankshaft. When the crankshaft turns, it turns the oil pump, creating pressurized lubrication flow. There are tiny oil paths or internal tubes to send the flow to the proper parts. Sometimes, parts are also oiled by way of "splashing" in the oil while it is in the oil pan. Seldom is that the ONLY way that parts are lubricated. By the way, often the pan and lower part of the engine from the oil rings around the pistons and down is called the crankcase; it is the "housing" for the crankshaft and related parts. Most parts that have bearing surfaces are lubricated from the inside out. There are tiny paths inside the components or inside the bearing structures, allowing the pressure to squirt the oil out onto the bearing surfaces. This is true of crankshaft to block surfaces, crankshaft to connecting rod bearing surfaces, connecting rod to piston pins or bearing surfaces, camshaft to block surfaces, thrust bearing surfaces, and similar connections. This holds true also for hydraulic lifters, reciprocating by motion of the camshaft, pushing the oil inside them, up through pushrods, then up through the block to the heads, to the rocker arms that open and close intake and exhaust valves. In the process, the valves themselves are lubricated in similar fashion, and, often by some splashing and spraying. In most engines, everything in the crankcase, is exposed to constant oil under internal pressure, spraying and splashes. The pistons slide up and down inside the cylinder with a group of usually, three piston rings near the top of the piston, to allow the compression in the combustion chamber, and to keep oil OUT of the combustion chamber. However, since without oil on the walls of the cylinder, friction would build, the piston and rings also oil the surfaces of the cylinder always on the up strokes, and on the downstrokes also, in some engines. Chains and gears are oiled by splashing and spraying of oil onto the surfaces. At points where parts such as the crankshaft or camshaft protrude through the block to the outside of the block to connect to other parts externally, seals keep the oil from leaking out. Where block surfaces join to other surfaces, such as at the oil pan, gaskets keep the oil from leaking out. Expansion and contraction of seals and gaskets through heating and cooling cause them to eventually leak in most car engines; seals also leak eventually from wear. As the last step in the lubrication process, after the oil has gone through all of the tubes and has done the lubricating jobs, it returns to the pan by dripping down and trickling down the inside walls of the engine. The process then continues. The vehicle has a fixed amount of oil in it, continually reused, that amount determined by the manufacturer's design of the engine. That quantity should NEVER be exceeded within the engine. Vehicle specifications vary in oil quantity from engine to engine, but most vehicle engines take 5 quarts of oil. Check your owner's manual for the correct values for your vehicle's engine.
To check the quantity of oil, there is a mechanical gauge, most often a stick or rod, usually called the dipstick, that extends from the outside of the engine to the oil pan. By way of markings on it, one can determine if the oil quantity in the engine is correct, or down by a measurable amount, usually a quart, perhaps two. Oil does not disappear; it is either burned (unintentionally) or leaks out. Neither is particularly good. Oil is introduced (added) into the engine either through an oil filler tube, or through a cap on the valve covers. Oil is drained from the engine at the lowest point on the oil pan where a drain plug is installed. Regularly, the oil quantity must be checked, refilled if needed, and eventually (how often is eventually), the oil and filter must be changed by draining and refilling.
On the vehicle's dashboard, there is also always an oil pressure indicator; it may be a gauge or a light. This gauge does NOT tell you the quantity but the pressure of the oil. If the pressure is too low for safe operation of the engine, the light will come on or the gauge will show the oil pressure in the caution or bad zone of the meter. You should NOT keep the engine running if oil pressure is low or there is none.
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