The Basic Function of Engine Oil

• Without getting into the technical details, you need to know that at its most basic level engine oil is a lubricant. Its job is to make sure that the moving parts of your engine don't rub together. If this were to happen, your car's engine would stop working and your mechanic would either rebuild or replace your engine, depending on the damage done.
  
  

Explaning the Numbers

• Two sets of numbers designate all motor oils sold today. The numbers are displayed as (Number) W (Number.)The first number is the oil's cold viscosity rating and the second number is the oil's hot viscosity rating. The "W" stands for winter and is the cold viscosity rating. This number tells you how easy the engine will start in cold weather. The lower this number, the easier the engine starts in cold weather.
  
  

5W-30 Pros and Cons

• The pros of 5W-30: It is best for operating in cold climates, and it tends to give slightly better engine protection. The cons of 5W-30: It might not be suitable for vehicles that operate in hot climates, and it is not the best option for vehicles that are involved in frequent city driving (stop and go) or vehicles that frequently haul heavy loads.
  
  

10W-30 Pros and Cons

• The pros of 10W-30: It is a better choice for vehicles that operate in hot climates; it is a better choice for stop-and-go driving; and it is a better choice for vehicles that frequently haul heavy loads. However, it is not as good as 5W-30 when used in extremely cold climates.
  
  

Expert Insight

• Tom and Ray Magliozzi of NPR's Car talk recommend that while it might not make a huge difference which oil you choose to put in your vehicle, it is never a bad idea to stick with your vehicle manufacturer's recommendations.