Every manufacturer has a specific recommendation or minimum requirement for the type of oil a given engine will use. You might wonder, what’s the difference between different weights, grades, and viscosity? What is the difference between 5W-30 and 10W-30? What do all of these numbers mean? Can’t you use any oil in your car or does it really matter?
Deciphering the Oil Code
Terms weight, grade, or viscosity are commonly used interchangeably and basically mean the same thing. They refer to the thickness or how easily the oil flows. Using a multi-grade 5W-30 oil as an example, this type is very commonly used in millions of vehicles. The first number followed by the “W” indicates the viscosity (or thickness) for cold weather temperatures. The “W” stands for winter. The lower this first number is, the less viscous, or thinner your oil will be in lower temperatures. Though it may seem trivial, the number is of major importance.
When engines first roar to life after turning the ignition key, the oil pump tries to push the oil from the low-lying oil pan to the top of the engine, to lubricate all of the moving parts (such as pistons, camshaft, etc.) Cold starts are the time of the hardest wear-and-tear imposed on the engine. The heavier (or thicker) the oil is, the harder the oil pump works and the longer it will take for the engine to receive the crucial oil lubrication it needs to prevent metal-on-metal friction upon start-up. So, a 5W- oil will flow faster and more easily than a heavier weight oil which would have a higher number like 10W- or 15W- oil.
The second number found after the “W” specifies the viscosity in hot temperatures. The higher the number means the thicker the oil will be at the optimum temperature. In older cars it was common to switch to different weights of oils depending upon the season. It’s a practice not as common today due to manufacturers building lighter-weight engines and using different engine materials than yesteryear. It is always recommended to follow the manufacturer’s fluid specifications found in your vehicle’s manual. Using a different weight of oil than what is recommended will likely result in decreased fuel economy or greater engine wear.
Are There Exceptions to the Rule?
The occasional exception to the “follow the manufacturer’s recommendation” rule comes into play when an engine has aged, and when the moving parts may have larger clearances between components. Thicker oils can sometimes improve performance and protection in such conditions, but for most vehicle owners, stick with the vehicle manual’s specifications.
What do the Manufacturers Say?
Some manufacturers will list a range of different types of engine oil dependent upon the climate where the vehicle will be used. A heavier-weight oil would likely be recommended for vehicles in southern arid areas such as Scottsdale, Arizona, while a lighter-weight oil may be better in cooler climates as can be found in Rapid City, South Dakota. Oil in South Dakota will obviously be subjected to colder engine start-up conditions during winter months than oil in Arizona during the same timeframe.
What is Straight Oil versus Multi-Viscosity Oil?
You should never use straight oil (SAE30, SAE40, SAE50, etc.) in a system designed for a multi-viscosity oil. Straight oils are used for smaller engines or older car engines manufactured before multi-viscosity oils were created. Even though snowmobiles, ATVs, and motorcycles have smaller engines than most passenger cars and trucks, straight oils are not to be used in such vehicles. Even regular automotive oils may not be appropriate due to specific engine designs, such as two-cycle versus four-cycle motors.
Take Care of the Engine You Depend Upon
All things considered, using the proper oil grade and changing your vehicle’s oil at regular, prescribed intervals are two of the most important preventive maintenance tasks you can do for your vehicle. Failure to do so can result in oil depletion, ultimately causing a seized engine. Most repairs related to improper or negligent oil management are both preventable and expensive. It is better to invest in good automotive service practices now than pay a painful repair bill later. Knowing the correct oil to put in your vehicle (and why) makes a good first step towards taking care of the engine you depend upon.