Ask Randy...

Q: Should I use synthetic motor oil for my car? What do the different oil viscosity numbers mean?

Auto Advice:
There’s no shortage of opinion on this issue, so not everyone will agree. But, here’s my take on synthetic motor oil usage: If the people who built your car recommend it, use it. Otherwise, you should only need to use synthetic motor oil if you have to go longer between oil changes. For example, a traveling salesperson that puts 3,000 miles a month on her car might not want to change the oil every month. In this case, synthetic oil could be used to extend the oil-change interval. Synthetic oil is able to maintain its viscosity (thickness) longer before it breaks down. If you change your oil on the recommended schedule, however, you shouldn’t need to switch to synthetic motor oil.

As for the different viscosity numbers, all motor oils thin out at high temperatures. The lower numbers (5W, 10W) are thinner and the higher numbers (30W, 40W, 50W) are thicker. Low viscosity oil flows more easily, so it’s recommended for most passenger cars in most climates. Multi-grade oils such as 5W30 or 10W40 can meet the requirements of a wider range of viscosities, so they’re better than straight-weight oils.

When in doubt, check your owner’s manual, or stop by any AAA Auto Repair shop to speak with an expert mechanic. Most passenger cars and light trucks in Arizona should be using 5W30 motor oil and having their oil changed every 3,000 miles. 

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