Though many of us still have a firmly ingrained opinion that we should change our engine oil every 3,000 miles, the interval is actually much more flexible and can change depending on the circumstances involved. The type of vehicle, driving environment, and oil type can all have a big impact on how fast the oil degrades. Here are three ways the oil type can affect the interval needed.
The viscosity, or thickness, of the oil you use is an important factor in protecting the engine from wear. It's a complicated factor to optimize because oil thins out as it gets hotter. This means that you need to use an oil that's the correct viscosity for your engine at operating temperature. The thinner the oil gets, the less buffer space it keeps between engine parts and the more wear it permits. The thickness of your oil will be greatest, of course, when you first start the car and before the engine has warmed up. The cold viscosity, known as the "winter" number, is placed before the operating temperature number and differentiated by a W, which stands for "winter." This method of expression creates numbers such as "10W-30" and "10W-40." But why is cold use important? The problem is that the oil gets so much thicker in cold temperatures that it doesn't circulate as freely through the engine as it does when hot. This means that the engine's best chance to grind itself together and achieve premature wear damage is while the oil is still warming up. So lower winter viscosity, one closer to the thickness of the hot oil, is better for your engine. If the oil you started out with is just on the edge of usefulness, then you'll have to change it sooner when its viscosity
2. Synthetic versus natural
Petroleum based oils have been in use longer, but synthesized oils are "made-to-order," so to speak, meaning that they often have more desirable properties than petroleum-based oils. For example, they tend to have smaller, smoother molecules and fewer impurities. In addition, they are better at blending a low winter viscosity with a relatively high viscosity at operating temperature. These factors add up to help synthetic oils last longer overall.
Some types of oil use many additives to help lubrication go more smoothly. If you have these additives in your oil, which is often the case with petroleum-based oils, they can help the oil last longer in some cases. However, they can also react with contaminants to change, over time, into something else that doesn't do the same job. So the help of additives has a limited shelf life, meaning that if you're depending on them, your oil also has a limited shelf life.
These three factors can have a big effect on how frequently you change your oil. Check your manufacturer's oil changing recommendations and then consider these factors to help you determine whether it's time for an oil change or not.
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