How an Engine Lubrication System Works

Let's follow Oliver the Oil Molecule on his journey around the engine!

Oil pan: This is where Oliver hangs out when the engine isn't doing anything; the oil lounge, if you will. In most cars, this pan holds about 4 to 6 quarts of oil.

Pickup tube: When the engine is switched on, it needs oil immediately. Oliver and his oil buddies get sucked up by the pickup tube and lined up for action.

Oil pump: The pump does the sucking so that Oliver can slide up that tube against gravity and then pressurizes the oil. Oliver and his little oil friends get jammed in together even closer. Let's hope Oliver remembered to put on deodorant today.

Pressure relief valve: If Oliver and his friends get too close they start to plan a riot, this relief valve gives them a bit of much-needed breathing space. It's the lubrication system's way of saying, "Settle down, kids."

Oil filter: While Oliver and his friends are allowed to pass into the engine, the filter stops any dirt and debris the oil may have picked up on its last pass through the system.

Spurt holes and galleries: Oliver giggles every time he says "spurt holes." He's really immature. These are the little holes drilled in the crankshaft or other parts of the system that allow the oil to coat the bearings and cylinders that need to stay lubricated.

Sump: After doing his job to keep the moving parts of the engine moving, an exhausted Oliver slides all the way down into the oil pan again, also known as the sump, to hang out until he's sucked back up the pickup tube -- and he's back on the job.

There are basically two types of oil systems in vehicles, both of which sound like types of walruses or something: wet sump and dry sump.

Most cars use a wet sump system. (The more you say it, the weirder it sounds. Wet sump. Wet sump.) That means the oil pan is at the bottom of the engine, and the oil is stored there. Remember Oliver the oil molecule's lounge? It's kind of like he has a table next to the dance floor at the club. And in this strange metaphor, the dancers are pistons and bearings.

The advantage of a wet sump system is its simplicity. The oil is close to where it will be used, there aren't too many parts to engineer or repair, and it's relatively cheap to build into a car.

Some cars, especially high-performance cars, use a dry sump system. That means the sump isn't underneath the engine -- in fact, it can be located anywhere within the engine compartment. After Oliver does his job in the engine, he doesn't just drip into the lounge. He goes to the VIP room away from the dance floor.

A dry sump system gets you a couple of bonuses: First, it means the engine can sit a little lower, which gives the car a lower center of gravity and improves stability at speed. Second, it keeps extra oil from soaking the crankshaft, which can lower horsepower. And, since the sump can be located anywhere, it can also be any size and shape.

Two-stroke engines, by the way, use a completely different type of technology. Scooters, lawn mowers and other two-stroke machines have the oil mixed right in with the gasoline. When the gasoline evaporates in the combustion process, the oil is left behind to do its slick business.

Sometimes you have to do this yourself, measuring the correct amounts before filling the tank. But sometimes, as in most motor scooters, there's an injection system that takes oil from the reservoir and mixes it with the gasoline for you in just the right proportions.