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Smooth Running: Engine Lubrication System Basics

Crankshaft Showing Oil Galleries

If the heart of your vehicle is the engine, then the heart of your engine is the oil pump. At the center of the engine lubrication system, the oil pump circulates oil to lubricate critical parts, wash away deposits and debris and cool your engine. Without the oil pump and enough clean oil, your engine is just a few revolutions away from becoming a lawn ornament. Today, we’re going to follow a drop of oil through your engine oil system.

Oil Sump or Pan, Strainer and Pickup Tube

Because the engine lubrication system is a semi-open system, the drop of oil starts and ends its trip here. There’s some minimal pressure in the oil pan and the rest of the crankcase, and oil is constantly dripping back down from the rest of the engine.

The oil pump draws oil from the oil pan, and a screen keeps bigger debris from getting in. If the oil has been neglected, it might get burned and/or in the strainer as a glob of sludge. For now, we’ll assume your oil has been well-treated.

Pump and Pressure Regulator

The mechanical pump is driven by the crankshaft, camshaft or timing chain, depending on the engine. The oil is now under some pressure, generally between 10 and 60 psi, depending on engine speed.

This simple valve ensures that enough oil pressure is present in the engine lubrication system. The oil pump keeps on delivering, so excess oil splashes back into the oil pan.

Filter and Cool Down

Now the oil passes through a fine paper filter to remove metal and soot particles that the strainer didn’t catch. The typical oil filter captures particles bigger than 25–30 micrometers (µm), about half the diameter of a human hair, while some filter down to as little as 5–10 µm.

If equipped, the oil’s next stop would be the oil cooler, which is basically a small radiator to help cool the oil a little.

Galleries and Spurt Holes

Now that the oil has been cleaned up, oil galleries go to different parts of the engine, distributing oil to lubricate moving parts and power hydraulic systems. Oil is also one of the main ways that heat is drawn out of the engine, particularly from hot cylinder walls and pistons.

Timing Chain Lubrication is Critical for LongevityHoles are drilled to allow oil to spray on areas that require cooling or light lubrication, such as valve stems, roller cams or the timing chain. Some automakers use tubes to direct oil spray to cool off the underside of the pistons.

Bearing Journals

Where critical lubrication is required, such as the crankshaft, connecting rods and camshafts, oil is delivered to precisely-machined journals, with clearances as little as 12.5 µm. Still, that tiny space is all the oil needs to keep metal parts from touching each other.

Hydraulic Systems

Many vehicles use hydraulic valve lifters or variable valve timing, which is electronically controlled by the ECM (engine control module), but the power to make it work is generated by the oil pump.

Over the 3,000–5,000 miles between the typical oil change, the oil makes that trip a few million times. Along the way, it goes through temperature and pressure extremes, picks up contaminants and condensation, and even gets burned a little, so the oil has somewhat of a limited lifespan. Don’t forget to change your oil regularly and use a quality engine oil for the best protection and long engine life.

Check out all the oil filters available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on your engine lubrication system, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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