Shade Tree Answer Man: Which Oil is Right for my Car?

In the first installment of a weekly series designed to shed light on some of the mysteries of car ownership, the Shade Tree Answer Man will tell you which motor oil is right for your car:

Walk into any auto parts or discount store’s auto section and you will be faced with a giant wall of motor oil, labeled with a jumble of letters and numbers and jargon. Of this seemingly endless selection, how do you know which one is right for your car?

What do the numbers mean? How about the W?

The numbers on motor oil indicate its viscosity – how well it flows through your engine. Lower numbers indicate thinner, lighter, and more easily distributed oils.

Some oils are considered “straight weight” in that their viscosity is the same cold as it is at operating temperature. Most modern vehicles take a variable weight oil, which is where the W (for “winter”) comes in.

The first number indicates the oil’s viscosity when cold, and the number after the W tells you how it will perform when your engine is running and fully warmed up.

This makes the task of lifting oil from the pan beneath your engine to the valve mechanisms at the very top (when your engine is cold and most vulnerable to damage) much easier on your oil pump.

Lighter oils will be more appropriate for smaller and newer engines; for example, my 1979 Jeep with a six-cylinder engine takes 10W40, while my 1988 Honda Accord with a four-cylinder motor takes 5W30.

So how do I know which one to use?

Read your owner’s manual. If you bought your car new it is in the glove compartment, and now would be a good time to take it to bed and read it cover to cover if you haven’t already.

I’m serious. Go get it now and put it by the bedside and thank me later.

But if, like me, your car has changed hands 17 times since it was new, your best bet is to find the manual online or call the dealership and ask someone in the parts or service departments.

There are also some good online resources, like Pennzoil’s oil selector (which will suggest only their brand, but more on this below) or any of the vast number of manufacturer and model specific sites and forums.