Back in the deep, dark recesses of time, there used to be a type of business called a "full-service gas station." Easy to find on many busy corners in the typical town, the full-service gas station featured "attendants" who would pump your gas, clean your windshield, and perform other auto-related tasks. Frequently they would ask, "Can I check under the hood for you?" If you said yes, they would open the hood of your car and do a quick survey of the various fluids a car needs to operate correctly, among them the antifreeze/coolant, windshield washer fluid, and engine oil.

Attendants determined the car's engine oil level by using a dipstick, typically a long metal measuring device that extends into the crankcase, a big oil reservoir beneath the engine's cylinders. Now and again, the attendant would discover that the engine oil level was below the requisite mark indicated on the dipstick. Typically, the attendant would then show you the level on the dipstick and ask you, "Should I add a quart?" Smart drivers said yes because maintaining the proper engine oil level is fundamental to keeping a vehicle's engine running well.

Of course, the scenario just described sounds like something out of a bygone era when poodle skirts were in vogue, and three networks ruled the television airwaves. Service at a gas station? It seems like an ancient fairy tale. 

Nevertheless, the fact remains that today's internal combustion engines need the proper oil level for precisely the same reasons as the cars of the full-service gas station era. One could make the case that an appropriate oil level is even more critical in today's engines, which are often highly stressed by technology like turbocharging, than it was for the engines of the "Happy Days" generation. 

Now we ask you this: When was the last time you opened your vehicle's hood to check its engine oil level? Yeah, we thought so.

An engine rarely runs entirely out of oil. Aside from extreme neglect over time – never checking or changing the oil – a sudden and catastrophic loss of engine oil is uncommon but not unheard of. 

For example, as you drive, you could run over an object that puts a hole in your oil pan, allowing the oil to drain from the crankcase. Within seconds, your oil level could drop to almost zero. Another example is during an oil change, during which an inattentive technician could fail to tighten the drain plug in the oil pan. As you drive, your engine oil could flow out onto the pavement rather than keep your engine lubricated. 

Both of these situations would likely result in costly repairs because, without oil, the various parts of your engine will destroy themselves and each other. The engine may even "seize," which means that its rotating and reciprocating components quit rotating and reciprocating.

And then it will be time for a new engine. Or a new car.

You might be wondering to yourself: Why does an engine need oil? And why is maintaining the proper oil level so important? 

First, it is valuable to understand that the high-tech internal combustion engine in a new car, truck, or SUV is a collection of hundreds of pieces that must operate in concert to provide the requisite power to move the vehicle. Many of those parts move, some of them thousands of times per minute. For example, the tachometer that shows crankshaft "revolutions per minute" (RPM) gives you a quick and obvious indication that critical components are moving with incredible speed over and over and over again. The pistons, rods, bearings, valves, lifters, and camshafts that enable an engine to produce power require constant lubrication, or they will wear out – and wear out in a very short period of time. 

Metal-on-metal contact, especially in the presence of extreme heat, will produce rapid parts failure and engine seizure. It is often said that the engine's oil is its lifeblood, and that is an apt description because, like the blood in your body, the oil is necessary for an engine to work. 

The typical engine has a large oil reservoir (the crankcase) that holds several quarts of oil. The oil is drawn from the crankcase oil pan into a tube called the oil pickup and is pumped throughout the engine, lubricating all those rapidly moving metal pieces that otherwise would quickly fail. The lubricating oil circulates through the engine and is cleaned of dirt and debris by the oil filter before it begins its circuit again, a kind of never-ending journey.

Maintaining the proper oil level ensures there is enough oil for the oil pickup to draw continuously when the engine is running. If the oil level is low, the oil pickup might not always be immersed in oil, which means that it will suck in air instead, and that can immediately lead to low oil pressure and a lack of oil where it is necessary for lubrication and cooling.

There are three primary causes of a low oil level: leaks, attrition, and owner inattention. 

Oil leaks are common in older vehicles. As a car ages, so too do the engine's gaskets, seals, and other connections that prevent the oil from leaking. Ultimately, they may start to drip oil, leaving a mess underneath the engine in locations where you regularly park the vehicle. If your car leaks oil, you need to check the fluid level regularly and keep it topped off until you can fix the leak.

While oil leaks cause oil levels to decline, the most common types of oil loss are attrition and a vehicle owner's lack of attention. If you don't maintain the proper oil level by checking it regularly and adding oil when needed, the oil level drops, and some parts of the engine won't receive the lubrication they need. This results in premature engine wear, and, over time, it can lead to expensive repairs.

Even if it doesn't leak oil, an internal combustion engine consumes some oil as a part of its normal operation. This occurs when the oil makes its way past the piston rings and into the engine's combustion chambers, where it burns along with the fuel. When oil consumption is excessive due to engine age or internal damage, a car's exhaust may be white and smoky and smell like burned oil. This is a sign that your vehicle requires a significant repair.

You can avoid this by regularly checking and changing your engine oil. Over time, the oil breaks down and gets dirty. Left unchanged, the oil degradation can cause premature engine wear. The owner's manual will tell you the proper oil change service intervals for your car.

Modern cars will warn a driver when the oil level is getting low. Typically, a warning light comes on, prompting a vehicle owner to check the engine's oil level. 

However, don't rely on your vehicle's oil pressure warning system to alert you to a low oil level. By the time the low oil level results in a warning light, significant damage might have already occurred, even if the engine isn't entirely out of oil.

Real insights from real owners

© 2022 J.D.Power. All rights reserved.

© 2019 J.D.Power. All rights reserved.