Let’s explain all of those confusing numbers, letters and terms to help you choose the right oil for your car.

Stick with the manufacturer's recommended motor-oil viscosity classification. For instance, if your car uses 5W-30 synthetic oil, upgrade to high-mileage oil with a similar 5W-30 rating.

That’s why we chose the Pennzoil Platinum Full Synthetic 5W-30 Motor Oil as our top pick: This synthetic engine oil offers excellent performance in extreme cold and washes away dirt as it flows ...