What does the SAE Viscosity rating on your Motoroil bottle mean?
Viscosity is the oil's resistance to flow or, for the layman, an oil's speed of flow as measured through a device known as a viscometer. The thicker (higher viscosity) of an oil, the slower it will flow. You will see oil viscosity measurement in lube articles stated in kinematic (kv) and absolute (cSt) terms. These are translated into the easier to understand SAE viscosity numbers you see on an oil bottle.
A W on a viscosity rating means that the oil’s viscosity has been tested at a Colder temperature. The numbers without the W are tested at 210° F or 100° C which is considered an approximation of engine operating temperature. In other words, a SAE 30 motor oil is the same viscosity as a 10w-30 or 5W-30 at 210° (100° C).
The difference occurs when the viscosity is tested at a much colder temperature. For example, 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature.
This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear.
Most automobile manufacturers recommend changing the oil at least once a year or between 3,750 and 7,500 miles (depending on vehicle manufacturer) in passenger car and light truck gasoline engines.
However, you'll discover when your read more closely that the once a year, or between 3,750 and 7,500 mile oil change (depending on vehicle manufacturer) is for vehicles that are driven under ideal circumstances. What most of us think of as "normal" driving is actually "severe service" driving. This includes frequent short trips (less than 10 miles, especially during cold weather), stop-and-go traffic driving, driving in dusty conditions (gravel roads, etc.), driving foothill roads and driving at sustained highway speeds during hot weather. For this type of driving, which is actually "severe service" driving, the recommendation is to change the oil every 3,000 miles or six months.
For maximum protection, most oil companies say to change the oil every 3,000 miles or three to six months regardless of what type of driving you do.
Do you need to change your oil every 3,000 miles? Most drivers are still under the impression that this is the case. The truth is that this interval is no longer necessary. Engine oil does get dirty and this dirt can clog engine parts but if your car is less than 5 years old – changing the oil every 3,000 miles is probably a waste of money, time and….oil.
Thanks to the improvements in high quality lubricants and tighter tolerances in manufacturing of newer vehicles, the recommendation by many automakers is now at 5,000, 7,000 10,000 or more depending on driving conditions.
Check with your car’s manufacturer. For example, Toyota recommends 5,000 for a 2005 Tacoma pickup but Honda says 7,500 for a 2002 Odyssey. A 2010 BMW 3 can go up to 15,000 before you change your oil.