What does 5W30 mean?

What do the numbers tell you?

W stands for winter. The number before it is the low-temperature viscosity grade. With the same hot grade, 5W-30 flows more easily in the cold than 10W-30.

The 30 is the high-temperature viscosity grade. It is not a temperature in degrees or a quality rating.

Same 5W30 grade, different oil

You see two bottles labelled 5W30 in a shop. Their viscosity grade matches, but their other specifications and manufacturer approvals may differ. Check your car’s full requirements rather than the grade alone.

Use oil that meets your engine manufacturer’s requirements. Check the handbook or ask your garage if you are unsure.

What 5W-30 measures

SAE groups oils using measurements. The winter grade includes tests for resistance during cranking and the ability of the pump to draw oil at low temperatures. A lower winter grade must meet requirements at lower test temperatures. That does not give you a universal minimum starting temperature for your vehicle. The manufacturer also considers the design of the lubrication system and how it has been tested.

The second grade covers viscosity when the oil is hot. It includes a measurement at 100 °C, while the actual oil temperature in your engine varies with conditions and load. Two oils in the same grade do not need to have identical viscosity at every temperature. The grade describes a range of characteristics.

Read the rest of the label

Alongside 5W-30, the packaging may list an API or ACEA category and a vehicle manufacturer’s code. These describe characteristics beyond viscosity, including performance in particular engine tests and compatibility with some exhaust aftertreatment systems. Products with the same viscosity can therefore serve different applications, even within one brand.

First identify the specification for your exact engine. Then find the technical data sheet for the product you are considering. Compare the entire code, including letters and suffixes. Pay attention to the wording. A formal approval and a lubricant supplier’s statement of suitability are different claims. If the handbook requires approval, check that the data sheet or the vehicle manufacturer’s documentation confirms it.

Choosing between two bottles

Imagine both labels display 5W-30 prominently. One lists the required manufacturer approval, while the other lists a different specification. The first provides the confirmation you were looking for. The shared viscosity alone provides too little information about the second. If the packaging is unclear, look up the precise product name and variant. A shop may sell several similarly named products.

At a workshop, ask which oil from the drum they use. The product name, viscosity and specification are more useful for your service records than a line that simply says ‘engine oil’. Record the date and odometer reading when the oil is changed. That gives you enough information to look up the same product when you want to carry a bottle on a long journey.

Check the level before topping up

Look up how to measure the level in your particular car. Conditions vary between dipsticks and electronic systems. Top up only when needed and follow the stated quantity and waiting time. If you see an oil pressure warning, follow the car’s safety instructions. A pressure warning calls for a different response from a low level message.