5W30 vs. 10W30 Engine Oil Viscosity: Which is Better?

Jerry Wilson
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What Do the Numbers Mean?

While different engine manufacturers may use different standards when discussing oil, one thing is constant: the 5W and 10W refers to 5 and 10 weight oil. It’s the weight of oil that will give you a viscosity heftier than water, but with a flow that isn’t too heavy.

To give you a comparison, 10W oil has a thicker consistency than 20W. 10W-30 just means that the viscosity is almost the same as straight 30 weight.

Here’s a breakdown of commonly used engine oil weights and their uses:

  • 0W (Zero weight) – Heavier than water, never used in engines.
  • 5W – Use this only in winter or in very cold weather if your engine starts up well in thinner oil, such as 10W.
  • 10W – Use for colder temperatures and stop using at a high temperature in the summer.
  • 15W – Good for mild driving at temperatures between 10C (50F) to 25C (82F).
  • 20W – A standard weight for performance engines or competition, maintenance, or use in typical climates.
  • 25W – Good for extreme cold weather.

Ideal Working Temperature

Remarkable things happen when liquid engine oil becomes hot and it’s those things that lubricate and cool your engine as it operates.

As oil heats up, its viscosity decreases. That’s all there is to it. Viscosity changes as oil heats up. That’s why oil that’s used during cold days has different characteristics than oil used during warm days.

After rigorous evaluations, tests and comparisons, most manufacturers (and cars) recommend using 5W30 engine oil in normal temperatures and switching to 10W30 in extreme temperatures.

In this article, we’re going to talk about viscosity and how it affects your engine, which oil viscosity should be used when, and what factors affect it.

When to Use Which

Viscosity and for What?

All oils have different applications. This is also true of viscosities, which are considered as a measurement of an oil’s thickness or thinness, depending on the application. Since the thickness of an oil is contingent on the rate at which it is flowing, it’s also important to know how quickly the engine is moving during the time of use.

Two measurements are most important when determining the proper viscosity for any engine: the cold cranking rating, and the flow rate. The cranking rate is reflected in the first number. This is the measure of the highest viscosity that the oil can achieve at 37 degrees Fahrenheit.

The second number indicates the ration of the oil’s flow rate to its active time in the engine after being shut off. This helps to determine the oil’s ability to maintain its viscosity longer, yielding better protection for the engine.

Many people today are mixing their own engine oil according to their own specs. Ever wonder why?


Which Is Better: 5W30 or 10W30?

Based on my research, 5W30 and 10W30 engine oil are both great for most cars. You can use one or the other based on the needs of your vehicle. If you have a newer car that requires a WQ-30 weight oil, you may have to pay a higher price for the 5W-30. Fortunately, they are both very affordable and can be found at most auto supply stores or online auto parts retailers.

In some instances, such as the one I tested, 5W-30 and WQ-30 weight oils perform identically. I did not find a significant difference in performance between the two different viscosities.

I prefer the slightly higher viscosity of the 5W-30 because it lasts through multiple spin cycles without thinning out. I’ve had no problems with my cars starting when they are cold in the morning when they have been sitting overnight.

This is an example of when viscosity matters more than the actual weight of the oil. I have also found that 5W-30 lasts better when at higher operating temperatures in my vehicles.