Which Engine Oil Is Right for Your Car?

 Walk into a shop and you will see dozens of oil bottles with numbers like 5W-30 or 10W-40. Choosing the wrong one can make an engine work harder and wear faster. Choosing the right one is easier than it looks.

Always match the oil to what your owner's manual asks for.
Photo by Rinald Rolle on Unsplash

How to read the numbers

Take 5W-30 as an example. The first number, with the W (for winter), shows how easily the oil flows when the engine is cold. A lower number means the oil flows more easily in the cold. The second number shows how thick the oil stays when the engine is hot.

Two things must match your car

1. The viscosity grade (for example 5W-30), as the manufacturer recommends.
2. The approval or specification your engine needs. These appear on the bottle as standards such as API or ACEA, or as a manufacturer approval. This matters as much as the grade.

Types of oil

• Mineral: the most basic type, made from crude oil.
• Semi-synthetic: a mix of mineral and synthetic.
• Fully synthetic: made to be more stable at extreme temperatures. Many modern engines require it.

Where to find the right oil

Your owner's manual is the best source. Some filler caps also show the grade. Online oil finder tools from oil brands can help, but check the result against your manual.

Common mistakes

• Choosing the cheapest oil without checking the specification
• Using a thicker oil "to protect an old engine" without advice from a mechanic
• Ignoring special needs, for example some diesel cars with a particulate filter need a specific low-ash oil

In an emergency, topping up with a different oil is better than driving with too little oil. Then change to the correct oil as soon as you can.

Golden tip: Keep your receipts and write down the oil you used. It helps at the next service.

Which oil does your car use? Tell us in the comments.

This article is for general information only. Cars differ, so always follow your owner's manual and ask a qualified mechanic if you are unsure.