The oil in a vehicle’s engine has one main purpose – to keep all of the components working properly. This reduces wear on the engine and its parts and ensures that everything works more efficiently and quietly. Keeping the engine oiled also reduces the cost of repairs and helps your vehicle last longer.

Where the oil goes in an engine

The engine must be oiled for smooth, efficient performance, but that includes various components within the system. Oil travels around the following parts of the engine when it is flowing correctly:

  • Oil pan: This is the place where the oil goes when the engine is shut off, most vehicles will hold between four and six quarts of oil.

  • Pickup tube: This tube picks up the oil from the oil pan when the engine is turned on.

  • Oil pump: The pump pressurizes the oil to pack it more tightly and pushes it up the tube.

  • Pressure relief valve: This reduces the pressure when it has gotten too high.

  • Oil filter: This removes dirt and debris that may have gotten mixed in with the oil from previous passes through the system.

  • Spurt holes and galleries: Holes that were drilled into the crankshaft and other components that allow the oil to pass through and coat cylinders, pistons and bearings.

  • Sump: This allows the oil to slide back into the oil pan to begin the process all over again.

Two types of sumps exist. The first is a wet sump, which is used in a majority of vehicles. In this system, the oil pan is located on the bottom of the engine where the oil is stored. This design is practical for most vehicles because the pan is located close to where the oil will be used and it is relatively inexpensive to repair.

The second type of sump is the dry sump, which is most often seen on high-performance vehicles. The oil pan can be located anywhere on the engine and be any shape and size. The reason for this design is that it allows the vehicle to sit lower on the ground, which can improve stability at higher speeds. Another bonus is that extra oil stays away from the crankshaft, which can reduce horsepower when too much oil is present.

What engine oil does

While the basic job of oil in the engine system is to keep everything running smoothly, it has several different tasks to achieve that goal. To understand the importance of oil in the system, you have to know the specifics of what it is doing.

First, the oil coats the moving parts so that when they touch other parts, they glide instead of hitting the others and making loud noises. Imagine two metal pieces moving against each other. Without the oil, they would scratch, dent and otherwise damage each other. With the oil between them, the two pieces slide past each other with no marks left behind.

Oil also cleans dust and debris from the working parts. This is the reason that oil must be filtered before it runs through the system again. It picks up dust and dirt from the various components as it moves back to the oil pan. Keeping the system lubricated prevents rust and corrosion. Water, road chemicals, and other substances can get in the engine and would cause rust over time if the oil didn’t keep the metal parts lubricated. As the oil moves around the pistons and bearings, it helps improve sealing so that air doesn’t get in and the engine doesn’t leak. Another use for oil in the engine system is that it carries heat away from the moving components so that the engine stays cooler.

Types of oil

Oils may be either petroleum-based or synthetic (non-petroleum) chemical compounds. They are usually a blend of various chemicals, which includes hydrocarbons, polyinternal olefins and polyalphaolefins. Oil is measured by its viscosity, which is also considered the thickness of the oil. An oil must be thick enough to lubricate the components of the engine while being thin enough to move through the engine. The outside temperature also impacts the viscosity of the oil, and it must be able to maintain proper flow even in low temperatures.

Most vehicles use petroleum-based oil. If you switch to synthetic oil and your vehicle is not designed for it, you can end up damaging your vehicle. Many vehicles begin to use oil if the regular oil is switched with synthetic. Using or burning oil means that it gets by the pistons and into the combustion chamber where it is burned off. The vehicle may produce smoke when this occurs.

Synthetic oil does provide many advantages if your car is designed to use it. This type of oil doesn’t react to differences in temperature and creates better fuel economy. It also provides reduced friction on the engine parts over petroleum-based oil. The engine will last longer and require less maintenance, which means more savings for the owner.

Grading the oil

When you see a carton of oil, you will notice a set of numbers. This is defined as the grade of the oil and is important when determining which oil you will use in your vehicle. The grade system is defined by the Society of Automotive Engineers, which is why you will sometimes see SAE on the oil carton.

The grading begins at zero and increases in increments of five to ten. For example, you will see oil grades of 0, 5, 10, 15, 20, 25, 30, 40, 50, and 60. After the numbers 0, 5, 10, 15, and 25, you will see the letter W, which means winter. This oil is better performing at lower temperatures. The grade 20 may also have a W in front of it but not always, depending on whether it is a hot or cold viscosity grade.

Multi-grade oil is common with vehicles today. This type of oil has special additives included to allow the oil to function in various temperatures. These additives are called viscosity index improvers. In practical terms, it means that vehicle owners no longer have to change out their oil every spring and fall to prepare for the changing temperatures as it was once common to do.

The SAE designates two grades to the oil. One is for the lowest temperature at which the oil can operate and the second grade is for the viscosity at a high temperature. For example, you will see an oil designated as SAE 10W-40. The 10W tells you that the oil has a viscosity of 10 in cold temperatures and a viscosity of 40 at high temperatures.

Oil with additives

In addition to the viscosity index improvers, some manufacturers include other additives to improve the performance of the vehicle or the way the oil works. For instance, detergents may be added to help clean the engine. Other additives may help prevent corrosion or neutralize acidic products in the oil.

Molybdenum disulfide additives have been used to reduce wear and friction and were popular until the 1970s. Many additives have not been proven to improve performance or reduce wear and have become less common in today’s motor oils.

Problems related to oil in a vehicle

When the lubricating system doesn’t work properly, it can cause serious damage to a vehicle. One of the most obvious issues is when a vehicle leaks oil. If the issue isn’t addressed, the vehicle could run out of oil. Your engine will quickly be damaged and need replacing when this happens. It often throws a rod or piston when it isn’t lubricated properly.

The first step is determining where the oil is leaking. A professional will find the leak and make the repair. It may come from a damaged or leaking seal or a gasket. If it is the oil pan gasket, it can easily be replaced. A leak in the head gasket can cause permanent damage to a vehicle’s engine, and the entire head gasket will need to be replaced. If your coolant has a light brown color to the liquid, this is an indication that the problem is a blown head gasket. This part is designed to keep the oil inside the engine compartment and away from the coolant and other systems.

Another issue is low oil pressure on the gauge in your dashboard. Low pressure can occur for various reasons. If the wrong type of oil is put in a vehicle, it can lower the pressure in the summer or winter. A clogged filter will also reduce the oil pressure. Other causes include rod bearings and crankshaft journals that need to be replaced.

Maintaining your lubrication system

To keep your engine in proper working order, you need to maintain the system. This means changing the oil and oil filter as recommended by your vehicle owner’s guide. You also must use only the grade of oil that is recommended by the manufacturer. If you notice any problems with your engine or an oil leak, you should have your car serviced by a mechanic right away.

This article originally appeared on as How the Engine Lubrication System Works and was authored by Joyce Morse.

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