Viscosity – “The property of a fluid that resists the force tending to cause the fluid to flow.” – Dictionary.com Unabridged, based on the Random House Dictionary, © Random House, Inc. 2011.
Have you ever wondered what the difference is between 10w-40, 5w-40, and 40wt motor oil? Motor oil viscosity is expressed as a number. Motor oils that are thicker have a higher viscosity number. Thinner motor oils have a lower number. Multiple viscosity oils carry with them a range of numbers, such as 10w–40. In this case the 10 is a representation of the motor oil’s viscosity when cold and is determined from tests conducted at temperatures below zero degrees Fahrenheit. The ‘W’ stands for Winter. The 40 indicates the viscosity of the oil when tested at an engine operating temperature of 212 degrees Fahrenheit.
Single grade motor oil, such as 40wt, has only one number to represent its viscosity. Single viscosity motor oils are rarely used in today’s modern engines. Polymers are added to single viscosity oil to make one oil behave like many. In this way a 0W–30 motor oil will flow like a 0W viscosity oil when cold and a 30 viscosity oil when hot.
Automobile manufacturers have focused on using lower viscosity oils to improve fuel efficiency. Thicker or higher viscosity oils require more energy to move throughout an engine than thinner oils.
Seasonal temperatures are important factors to consider when choosing the right motor oil. Cold winter temperatures and summer heat affect the rate at which motor oil flows. The measure of this flow is the viscosity rating you see displayed on containers of motor oil.
Cold weather viscosity is crucial to the health and survival of an automobile engine during the first few seconds of extreme cold weather operation. You’ve heard the saying “slower than molasses”, right? This definitely applies to motor oil. Engine damage may occur if motor oil is too thick due to cold temperatures and is unable to flow in-between engine parts – especially during cold weather startups.
The best resource for deciding which oil viscosity to use during the year may be found in the vehicle owner’s manual. Switching from a 10W–30 to a 5W–30 during the winter months might be a great choice for a vehicle operated in an area that typically sees the thermometer dip below the zero mark. In the Inland Northwest, our winters can be pretty brutal. If your vehicle’s manual suggests switching oil types, we strongly suggest that you follow their recommendations.
With the correct viscosity determined the next choice in motor oil is type. The best strategy is to again follow what the vehicle owner’s manual recommends. Higher mileage blends can benefit engines over 75K miles. Synthetic blends and full synthetics can bring additional protection and often flow more easily during severe cold then conventional oils. Don’t forget that stop–and–start driving during winter or summer months is considered severe duty in most manufacturer maintenance schedules. Changing the oil and filter according to this schedule can save expensive engine repairs and extend the life of your vehicle.
Silverlake Tire & Auto is a full service auto repair business. We are the only ASE Blue Seal of Excellence service facility within 100 miles of Coeur d’Alene. We’re also an AAA approved auto repair facility. If you have any questions regarding what type of oil to use in your vehicle, please feel free to call us at 208-772-6081. We would be happy to discuss all of the available options for your vehicle and we would count it a privilege to service your vehicle.
