Oil may play a supporting role in the combustion engine, but without it, the parts wouldn't be able to move freely, the seals would dry up and crack and little bits of dirt and metal would clog the works. Without engine oil, the whole combustion process would grind to a halt.
Most drivers know their engine needs oil just like it needs gasoline, but how much, what kind and how often to add it can seem like a mystery -- especially with recent advances in modern engine technology. New drivers, as well as experienced drivers who've just upgraded to a brand-new car, can benefit from learning the basics of engine oil. After all, it's one of the few things in an engine that the average driver can learn about and control.
Keep reading to learn the five things everyone should know about engine oil -- it's as easy as it is empowering.
One of the first choices a driver is faced with, whether the car is brand-new or high-mileage, is between mineral and synthetic engine oil.
In a nutshell, mineral oil is the stuff that comes from the ground and is created as part of the oil refining process. This type of oil has been around as long as cars have been around, and it's less expensive than synthetic oils.
Synthetic oils are more expensive because of the chemical engineering involved in creating them. They still have a base mineral oil, but they've been engineered to allow for more miles to be driven between oil changes, and they often have additives to help keep the oil cleaner, longer. It's also more stable at higher and lower temperatures than mineral oil.
Speaking of temperatures, let's take a look at what those numbers on the bottle mean.
It's intimidating when you see those bottles of engine oil lined up along the shelves, each promising to keep your engine cleaner, improve your fuel efficiency and more. And every one of them has cryptic letters and numbers on the front.
Those letters and numbers tell you what the oil's viscosity rating is (some people call this the oil's weight). Viscosity is a measure of how easily the oil flows -- is it thick or thin? The Society for Automobile Engineers (SAE) tests all engine oil at 210 degrees Fahrenheit (98.9 degrees Celsius), a typical engine operating temperature, and gives it a rating from 20 to 60. On the bottle, it will say something like SAE 20 or SAE 30, two common viscosities.
If you live in a colder climate, the label will be a little different. It will likely say something like 5W-30. The "5W" means that the SAE has tested the viscosity of the oil at a colder temperature. This oil will be thinner when you start the engine on a cold morning but will perform like an SAE 30 oil at 210 degrees Fahrenheit (98.9 degrees Celsius), when you've been driving a few minutes and the engine is warm.
In any case, your owner's manual will likely have a suggested oil rating for your car. A trusted mechanic will be able to help you choose, too. Just remember that colder starts need a thinner oil at first, and warm engines need a thick enough oil to not disappear when the engine becomes warm.
Next up: The oil change.
For decades, there was one basic rule for changing the oil in your car: every 3,000 miles (4,828 kilometers) or 3 months, whichever came first. Easy, right?
However, with the advances in engine performance and design, plus the advances in engine oil technology, most cars can go farther between oil changes. But how far?
Many modern cars can go 5,000 or even 10,000 miles (8,047 or 16,093 kilometers) between oil changes, depending on the model and how you drive. Most people won't go wrong with a 5,000-mile (8,047-kilometer) interval between changes, but if your daily commute involves lots of stop-and-go driving, you might want to change it a little sooner.
Some cars can even keep track of the oil and alert the driver when it's time for a change. Chris Martin of Honda says his company's Maintenance Minder, for instance, "monitors engine operating conditions and accumulated engine revolutions to recommend specific maintenance, like oil changes, when it's actually required, rather than relying on a set maintenance schedule." This keeps the engine in its best shape and saves the owner money on maintenance.
Next, the easiest of all maintenance: Checking your oil.
This is one car maintenance practice that hasn't changed much over the years. Just about anyone can do it, and it has the added benefit of getting you to lift your hood and actually see what your engine looks like.
Most of the engine will be encased in some kind of cover with a lot of wires and hoses coiled around it. But somewhere in there, usually toward the front, you'll find the dipstick. It likely has a loop or hook on the end for pulling it out.
When the engine is cool, pull out the dipstick and wipe off whatever you find on the end with a towel. Notice the markings at the end of the stick -- the minimum and maximum levels are marked, sometimes with crosshatching between them or even holes in the metal. Put the dipstick back into the engine and pull it out again. Now check to see where the oil level is. It should be closer to the maximum than the minimum, but not over full.
It's okay if the oil is brown or black; that just means it's doing its job. Replace the dipstick, wash your hands, and feel good that there's still something in the engine compartment that you can take care of.
Wait -- was the level low? Well there's more you can do, then. Keep reading to find out how to safely add oil to your engine.
You've checked the oil, and it was a bit low. No big deal -- just add a bit more. Quarts of oil are pretty cheap; if you're comfortable with the viscosity rating recommendation for your car, you can pick up oil almost anywhere, including big box stores and even some grocery stores. If you'd like a little hand-holding, the local auto parts store would be able to help.
With a cool engine, use the dipstick to check your oil to see exactly how low it is. Locate the oil cap on top of the engine and unscrew it. Using a funnel, add about half of the bottle of oil, wait a minute or two, then check the dipstick again. You don't want to overfill the engine.
When the oil level is just below maximum, screw the oil cap back on and make sure the dipstick is back in place. The funnel should have kept the whole process fairly neat and tidy, but if any oil spilled onto the outside of the engine, it's not the end of the world. However, you'll likely smell it burning off the next time you drive.
For more information about engine oil and other related topics, follow the links on the next page.
Are you a vehicle aficionado? See how much you know about horsepower and torque by taking this quiz at HowStuffWorks.
- Chinn, Kevin. Global Flagship PVL Technical Advisor, ExxonMobil Lubricants and Specialties. Personal interview on Feb. 11, 2009.
- Consumer Reports. "How to Check Your Car's Engine Oil." February 2011. (May 26, 2011) http://www.consumerreports.org/cro/cars/tires-auto-parts/car-maintenance/how-to-check-your-cars-engine-oil/overview/index.htm
- Martin, Chris. Honda Public Relations. E-mail correspondence on May 11, 2011.
- Upmpg.com. "Motor Oil Viscosity Grades." (May 26, 2011) http://www.upmpg.com/tech_articles/motoroil_viscosity/
- Weisbaum, Herb, "How often should motor oil be changed?" Msnbc.com. April 17, 2006. (May 26, 2011) http://www.msnbc.msn.com/id/12359794/ns/business-consumer_news/t/how-often-should-motor-oil-be-changed/