A well-running oil system is critical to your engine’s health. Oil keeps the engine’s internal metal parts lubricated to reduce the wear and tear caused by friction. Your engine could literally self-destruct if it runs out of oil so a properly maintained oil system is key.

The Engine’s Lubrication System

The oil pump draws oil from the oil pan, then forces it through the filter, into the crankshaft passage, through the connecting rods to the pistons and rings. Oil is pushed through the lifters and pushrods, and covers the rocker arms. It then flows back down into the pan to complete the cycle.

Oil Pump

The oil pump is used to force pressurized oil to the various parts of the engine. Gear and rotary pumps are the most common types of pumps. The gear pump consists of a driven spur gear and a driving gear that is attached to a shaft driven by the camshaft. The two gears are the same size and fit snugly in the pump body. Oil is carried from the inlet to the delivery side of the pump by the opposite teeth of both gears. Here it is forced into the delivery pipe. It can’t flow back, because the space between the meshing gear teeth is too tight.

The rotary pump is driven by the camshaft. The inner rotor is shaped like a cross with rounded points that fit into the star shape of the outer rotor. The inner rotor is driven by a shaft turned by the camshaft. When it turns, its rounded points “walk” around the star shaped outer rotor and force the oil out to the delivery pipe.

Oil Seals

Oil seals are rubber and metal composite items. They are generally mounted at the end of shafts. They are used to keep fluids, such as oil, transmission fluid, and power steering fluid inside the object they are sealing. These seals flex to hold a tight fit around the shaft that comes out of the housing, and don’t allow any fluid to pass. Oil seals are common points of leakage and can usually be replaced fairly inexpensively. However, the placement of some seals make them very difficult to access, which makes for a hefty labor charge!

Engine Oil Dip Stick

The engine oil dip stick is a long metal rod that goes into the oil sump. The purpose of the dip stick is to check how much oil is in the engine.

The dip stick is held in a tube; the end of the tube extends into the oil sump. It has measurement markings on it. If you pull it out, you can see whether you have enough oil, or whether you need more by the level of oil on the markings.

Oil Filler Cap

The oil filler cap is a plastic or metal cap that covers an opening into the valve cover. It allows you to add oil when the dipstick indicates that you need it. Some cars have the crankcase vented through the filler cap. Oil which is added through the filler passes down through openings in the head into the oil sump at the bottom of the engine.

Oil Filter

Oil filters are placed in the engine’s oil system to strain dirt and abrasive materials out of the oil.

The oil filter cannot remove things that dilute the oil, such as gasoline and acids. Removing the solid material does help cut down on the possibility of acids forming. Removing the “grit” reduces the wear on the engine parts.

Modern passenger car engines use the “full flow” type of oil filters. With this type of filter, all of the oil passes through the filter before it reaches the engine bearings. If a filter becomes clogged, a bypass valve allows oil to continue to reach the bearings. The most common type of oil filter is a cartridge type. Oil filters are disposable; at prescribed intervals, this filter is removed, replaced and thrown away. Most states now require that oil filters be drained completely before disposal, which adds to the cost of an oil change, but helps to reduce pollution.

Oil Passages

Within the engine is a variety of pathways for oil to be sent to moving parts. These pathways are designed to deliver the same pressure of fresh lubricating oil to all parts. If the pathways become clogged, the affected parts will lock together. This usually destroys parts that are not lubricated, and often ruins the entire engine.

The oil passages are cleverly drilled into the connecting parts of the engine, which allows the highly mobile ones (like the pistons) to have ample lubrication. Originating at the oil pump, they flow through all of the major components of the engine. In the case of the pistons and rods, the passages are designed to open each time the holes in the crankshaft and rods align.

Oil Pan

At the bottom of the crankcase is the container containing the lifeblood of the engine. Usually constructed of thin steel, it collects the oil as it flows down from the sides of the crankcase. The pan is shaped into a deeper section, where the oil pump is located. At the bottom of the pan is the drain plug, which is used to drain the oil. The plug is often made with a magnet in it, which collects metal fragments from the oil.

Oil Weights

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE’s low temperature requirements have a “W” after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. You will hear them referred to as multi-viscosity, all-season and all-weather oils. When choosing oil, always follow the manufacturer’s recommendation.

Synthetic Motor Oil

One of the most respected engine builders of all time, Smokey Yunick, states that synthetic oil is superior in all areas of lubrication. Smokey has his favorite brand, but we feel that all major brands of straight synthetic will provide superior lubrication. We do feel that many owners use heavier weight oil (both conventional and synthetic) than is necessary. For example, 50 wt. or 20-50 racing oil is necessary for racing engines that have bearing and operating clearances set for that weight of oil, but our factory style engines do not need such heavy oil. Extremely heavy oil, and/or very high pressure oil pressures add excessive load on the oil pump, which causes accelerated wear on the distributor drive gear, and costs valuable horsepower to the engine. Given improvements in motor oil since the era of the muscle cars, we can probably safely use even lighter weights of oil than originally recommended by the factory.