Can You Interchange 10W-30 And 5W-30 Motor Oils?

Engine oil is essential for cars with internal combustion engines. It lubricates the engine's internal parts, like the camshaft(s), crankshaft, and pistons, as well as helps with heat dissipation. But while every engine requires oil, not all engine oil is the same. This liquid can come in various viscosities or thickness classifications, depending on the type of engine with which it's designed to work. Of those different viscosities, two of the most commonly used in many modern cars include 10W-30 and 5W-30.

To understand the differences between these two oils, we have to look at the numbers that make up the code or classification. Each number and the letter "W" have a meaning — for 10W-30, the code means that the oil has a viscosity or thickness rating of 10 when the engine is cold, as indicated by the letter W, which stands for winter, and a viscosity rating of 30 when the engine is warmed up to its normal operating temperature. The 5W-30 oil has a viscosity rating of 5 when the engine is cold and the same viscosity rating of 30 once the engine is warm. That means that 5W-30 is thinner at colder temperatures than 10W-30, but the two oils have the same viscosity rating when the engine is up to temperature.

Based on this information, you may wonder if it's okay to mix the two types of engine oil. While the safest move is always to use the oil your vehicle manufacturer recommends, there are times when you can switch between 10W-30 and 5W-30 oil. As a former professional auto mechanic, I'll explain why.

Many cars can use both 10W-30 and 5W-30 oil, which you can confirm by reading your owner's manual or by checking the oil fill cap in the engine bay. If that's the case, your engine oil fill cap will most likely list one primary or preferred oil, with the manual providing a few different oil types you can use in the engine.

If your vehicle is designed to use only one of these oils, though, there are other factors to consider. Because 5W-30 oil is thinner at colder temperatures than 10W-30, you shouldn't use it in place of 10W-30 if you live somewhere very chilly. The 5W-30 oil may not provide sufficient lubrication in such a cold environment, and could result in extra friction and mechanical damage. On the other hand, using 10W-30 in a car built for 5W-30 could prevent the oil from moving smoothly through the engine, making it more difficult to start in cold weather. Basically, you should avoid swapping between 5W-30 and 10W-30 if you live in a region with freezing weather.

However, if you live somewhere warm, using 5W-30 or 10W-30 is unlikely to make a difference, as both oils perform identically once the engine is warm. In hot climates, the engine may reach its optimal operating temperature very quickly, resulting in little to no difference in performance. All that said, remember that using the oil your manufacturer recommends is always the best move for your car. The prices of most standard oil viscosities are very similar, meaning there's rarely a reason not to use the correct oil type.