Everything You Wanted to Know about Motor Oil (But Were Afraid to Ask)

If you're like me, you've never give much thought to motor oil. You know that it's important to your car; you know that it lubricates your engine; you know that you really, really should change it every 3,000 miles. What else is there to know?

As it turns out, a lot. Let's say you're conducting your weekly car check-up when you discover that your oil is low. Or--if you haven't been conducting your weekly check-ups--let's say you're driving along and that ominous oil light comes on. (Take a look at Car Care 101 if you want to make sure you never find yourself in this position.)

Either way, you need to top off your oil. No sweat, right? You'll just swing over to your local auto supply store to buy an extra quart. But at the store you discover--in a long, mystifying row of shelves--a dizzying assortment of different types and brands of motor oil. It's worse even than the shampoo aisle at the supermarket.

Which oil is right for your car? What happens if you pick the wrong one? And why is that clerk snickering at you?

You'll find the answers to these questions and more in our one-stop guide to oil literacy...

Read Your Owner's Manual

Whether you're at a mom-and-pop gas station or an auto-parts superstore, the motor oil aisle can be confusing-if you don't know how to read the labels. 10W-40, 5W-30, 15W-50 . . . what's it all mean?

First things first: READ YOUR OWNER'S MANUAL. I have always been too lazy to do this until recently. I discovered that my owner's manual is really quite informative. Once I got past the holographic foil logo on the cover (oooh, aaah) I perused the index and found an entry for "Oil, Engine, Recommendation." Bingo.

While flipping to the correct page, I discovered an engine maintenance schedule, a diagram of the engine showing where the various engine fluids are to be added and where dipsticks are located (very handy), and finally, the recommended oil for my car: 5W-30. Chances are your manual will say the same thing if your car was made after 1989. My manual gives me the added flexibility of choosing 10W-40 under certain conditions. (More about that later.)

While you're reading the manual, it's also a good idea to check if the use of certain types (or grades) of engine oil will void your warranty, and if synthetic oil or oil additives are recommended for your car.

How to Read a Motor Oil Label

5W-30: What does that mean? And what's the difference between that and 10W-40? Is a higher number better? Or is it like golf, where the lower number is more desirable? Me, I always confuse 10W-40 with WD-40. (Luckily, I know better than to spray the oil on my engine.) However, my confusion always predisposed me to choose 10W-40, which as we now know, was the wrong choice. (Oops.)

The numbers on a motor oil label indicate the viscosity (also known as the grade) of the oil. Viscosity is the thickness of the oil. More precisely, it is a measure of how well the oil flows at a given temperature. Oil is like molasses--it pours better off the shelf than out of the refrigerator.

You will notice on a motor oil label that the letters SAE always precede the grade of the oil. SAE stands for the Society of Automotive Engineers, which sets the standards for motor oil viscosities and hundreds of other automobile parts. SAE assigns a number (0, 5, 10, 30, 40) for a range of oil viscosities at a given temperature. The lower numbers are thinner, or have a lower viscosity. The higher the number, the thicker the oil. A motor oil designated SAE 30 (a single-grade motor oil) is therefore thinner than one labeled SAE 40.

Single-grade oils, however, are reserved for special uses, such as lawnmowers. Unless you're driving your lawnmower about town, choose a multigrade motor oil-one with two numbers.

Multigrade Motor Oils

Multigrade oils do something remarkable: While a single-grade motor oil is thicker in cold weather and thinner in hot weather, multigrade oils maintain their thinness at lower temperatures. This ensures that, in cold weather, the oil will flow well enough to cycle through your engine. As the temperature of the engine (or the weather) increases, special agents in the oil cause it to thicken. This allows the oil to maintain a strong protective film over your engine's parts.

Understanding an oil label isn't difficult. The first number of a multigrade motor oil is its viscosity in cold weather. The W after the first number stands for "winter." A 5W-30 motor oil, then, has an SAE rating of 5 at 0?C (32?F, or freezing). The second number is the viscosity of the oil in higher temperatures: 100?C (212?F). Whereas an SAE 5 motor oil would get dangerously soupy at 100?C, a 5W-30 motor oil only thins as much as an SAE 30 motor oil would.

What Is Motor Oil, Anyway?

Conventional motor oils are refined from crude oil. About 1% of the volume of a barrel of crude is turned into motor oil. An average bottle of motor oil is only about 80% oil, however. The other 20% is made up of oil additives. These additives include the special agents that make multigrade oil possible plus:

detergents that prevent sludge buildup;

rust inhibitors that counteract the water vapors and acids that build up with normal engine use;

antifoaming agents to collapse tiny air bubbles that can create wear on your engine;

pour-point depressants that allow the oil to flow better at lower temperatures; and

oxidation inhibitors that slow down the natural deterioration of motor oil over its lifetime in your car.

The types and proportions of additives in a given brand of oil may vary, and that's why some oils claim to make your engine cleaner (they contain more detergents) or claim to be better for high-mileage cars (they contain special lubricants and sealants).

Synthetic Motor Oil

There are several synthetic motor oils on the market now. I went to a local auto superstore and asked why someone would choose synthetic (or synthetic blend) oils over conventional oils. My confidential source (we'll call him Deep Stick) advised me that synthetic oils increase your gas mileage and, because they don't break down as quickly as conventional oils, they keep your engine cleaner and maintain their viscosity longer. Synthetic oils also don't contain particles found in natural oil that may produce sludge and damage your engine.

How to Choose Your Motor Oil

You've read your owner's manual. You know how to read a motor oil label. Now you're faced with umpteen brands of motor oil, all the bottles claim different things, and you're looking forward to a game of eeny-meeny-miny-mo.

Stop right there! There is one more thing you must take into account: temperature. Specifically, the range of temperatures you expect your car to encounter.

If you live in an area where winter temperatures routinely dip below freezing, you'll want a motor oil with a lower viscosity at those temperatures. 5W-30 fits most cold environments, but a 0W-30 synthetic oil is available for truly extreme conditions.

If you rarely (or never) encounter freezing temperatures, you may wish to choose a 10W-30 oil. If you never face freezing temperatures, but you experience burning hot summers, a 10W-40 may be in order. My owner's manual allows me the flexibility to choose 10W-30 if ambient temperatures do not fall below 0?F.

Brand Differences

Deep Stick, my source at the auto parts superstore, informs me that all brands of motor oil are pretty much the same. But by all means, read the labels. They can give clues as to the particular additive mix in a certain brand of oil, and you may find one that seems more appropriate to your car and driving conditions.

Motor Oil Dos & Don'ts

Do ask for a paper cone or funnel when you buy a quart of oil. I have discovered it's a lot easier to pour the oil this way. Otherwise, you may end up lubricating the OUTSIDE of your engine, which is pretty gross, and once the engine gets hot, the oil will burn and stink.

Do get your oil changed every 3,000 miles, even if the oil label or your owner's manual specifies a longer interval. If you drive stop-and-go, in cold weather, or make frequent short trips (as most of us do), you will need your oil changed every three months or 3,000 miles, whichever comes first.

Do look on the label for the letters SAE before the viscosity indicators, and also look for what is called the API donut on the back label. This circle-in-a-circle label tells you whether the motor oil meets the standards set by your car manufacturer. It also tells you whether your oil is energy conserving. (See illustration.)

Don't mix grades of oil. Mixing a quart of 5W-30 with a quart of 10W-40 will not give you 7.5W-35. Oil manufacturers caution that mixing grades of oil will unbalance the additives that control viscosity at various temperatures.

Don't overfill your crankcase. This may cause foaming in your oil.

Motor Oil Glossary

4-cycle engine: most passenger cars are 4-cycle engines. Don't buy an oil for 2-cycle engines.

conventional: motor oil refined from crude oil.

crankcase: The metal casing with the hole in the top where you put the oil.

dipstick: a metal rod that shows the level of oil in your engine.

grade: the viscosity of your oil. Oils labeled with two grades (5W-30) are multigrade.

synthetic blend: part conventional, part synthetic motor oil.

synthetic: motor oil that has undergone a special chemical process.

viscosity: the thickness of the oil, or a measure of how well it flows at a given temperature.

How I Fought the Man and Won: The Day Jiffy Lube Blew Up My Car

I needed my oil changed, desperately. Doug, my mechanic and the only person I've let touch my car for years, had a four-day waiting list. I felt like I was cheating on him, but the seduction of a cheap oil change in less than fifteen minutes was more than I could resist. I took my car to Jiffy Lube.

If I'd only known the hell I was in for, I'd have sped off in the other direction. For starters, the promise of an oil change in fifteen minutes turned out to be a big lie. I spent more than an hour drinking bad coffee and watching Sally in the waiting room.

After a mechanic finally worked on my car, he told me I needed to replace three parts. If he'd just said one, I'd probably have said okay. But three? Come on. They've gotta know that not all women are gullible when it comes to cars. I made him show me the parts. Finally, I agreed to a new air filter (I could see for myself how dirty it was) but nothing else. Mostly, I was just grateful to pay my bill and leave.

"Your car is on fire!"

I hadn't driven a mile when I stopped at a light and a woman came running toward my car, waving her arms frantically. I figured she was nuts, especially when she started beating on my window. But then I heard what she was screaming: Your car is on fire!

I pulled over and sure enough, flames were coming out from beneath my hood. The not-so-crazy woman was already on her cell phone calling the fire department. Within a few minutes, two fire trucks arrived and put out the flames. After a quick investigation, one of the firemen brought me a charred cloth.

"Here's your problem," he said. "Somebody left this oil-soaked rag on your engine."

I turned around and took that rag right back to Jiffy Lube, where I asked to speak with the manager. My request was more than reasonable: I wanted a refund and I wanted Jiffy Lube to pay for any damage to my car. But her response blew me away.

"That's not our rag," the manager barked. "Our rags are pink and that one is white. You must have left that one in there."

I tried to explain to her that chemicals from the fire extinguisher had probably discolored the rag. Besides, wouldn't her mechanic have noticed if there had been another rag on the engine? By now, I was throwing a fit loud enough for everyone in the waiting room to hear: Jiffy Lube had caught my car on fire and they were lucky they weren't paying hospital bills.

When she realized I wasn't going anywhere until I got what I wanted, she admitted that she didn't have the authority to refund my money. I would have to speak with a regional supervisor.

For the next three days, I called the supervisor pretty much every hour. At first, he took the manager's side, claiming it wasn't their rag. Then his boss cut the rag in half, revealing pink fibers in the center. They finally agreed to pay my mechanic to check out the car and fix any damage resulting from the fire.

"What about a refund?" I asked.

"You still are benefiting from the services we provided," he replied. "I'll just send you some coupons for your next oil change."

Like I'd ever go back there.

I told him that if I didn't get a refund, I was going to make his life ten times more miserable than I'd already made it. I had my money the next day.

Know your rights

According to Jocile Ehrlich, president of the Better Business Bureau of Cincinnati, if a mechanic gives you trouble, you should take the following actions:

1. First, speak with the manager of the shop. Be sure to document your conversation.

2. If you're unable to reach an agreement, and if the company is a franchise, direct your complaint to the owner of the franchise. A phone call might work, but a written complaint provides better documentation.

3. If you're still unable to come to terms, send a written complaint to your local Better Business Bureau. The Bureau will send a copy of your letter to the shop, encouraging them to settle the complaint.

4. Still haven't achieved a satisfactory result? Your next option is legal action. If you want to play hardball, you can file a complaint in small-claims court. (Most county courts can provide you with a handbook outlining this procedure.) If softball is more your style, you can try mediation or arbitration. Mediation brings both parties together with a facilitator who helps the two parties resolve the complaint. Arbitration makes a ruling that is legally binding. The Better Business Bureau offers help with both of these options.

I'll never stray again

After Doug had a good laugh at my Jiffy Lube story, he gave my car a thorough inspection. Nothing was wrong, he said, not even those other two parts that Jiffy Lube had tried to sell me. And then he did something unbelievable--he said I didn't owe him anything for the check-up.

"You don't know what I've gone through to be able to pay you," I explained. Then he said he'd take fifteen dollars. I wrote him a check for twenty-five.