Buy 5W-40 engine oil

5W-40 is the grade for engines that are worked hard thermally: turbodiesels, charged petrol engines, cars used for towing and anything that sees a lot of full load. The same cold start as a 5W-30, but distinctly more oil film at operating temperature. Which approval your engine needs is shown by the oil finder.

When 5W-40 is the right choice

The difference from 5W-30 lies entirely in the warm engine: at 100 °C a 40 grade carries noticeably more load. That counts when oil temperatures sit high for long periods - turbochargers, trailers, mountain passes, motorway at full throttle, summer traffic jams.

Typical vehicles:

  • European turbodiesels, particularly older TDI and CDI engines with no long-life specification
  • charged petrol engines with ACEA A3/B4 in the owner's manual
  • high-mileage vehicles that measurably use oil on a 30 grade
  • vans and light commercial vehicles in continuous service

5W-40 is not suitable where the manufacturer expressly requires a thinner oil with a low HTHS viscosity: modern long-life vehicles, hybrids and anything specified on 0W-20.

A3/B4 or C3 - two completely different 5W-40 oils

This distinction is the most common mistake when buying a 5W-40.

**ACEA A3/B4** is the classic high-performance oil with no limit on ash content. It has the greatest reserves, but it does not belong in a vehicle with a diesel or petrol particulate filter.

**ACEA C3** is the Low SAPS variant: reduced ash, phosphorus and sulphur content, so the filter does not clog. It is available in 5W-40 as well.

Both show the same viscosity on the label and are still not interchangeable. If your vehicle has a particulate filter, the way through is the C class or a manufacturer approval that includes it.

Common approvals for 5W-40

  • MB-Approval 229.5 - Mercedes-Benz without particulate filter, high performance reserves
  • MB-Approval 229.51 - Mercedes-Benz with particulate filter, Low SAPS
  • VW 502 00 and 505 01 - VW Group petrol engines and pump-injector diesels respectively
  • BMW Longlife-04 - BMW and Mini
  • Porsche A40 - approved oils for most Porsche models

If your approval is missing here, the owner's manual or the oil finder decides - not the similarity of the numbers.

Fully synthetic, and what that gives you day to day

5W-40 is practically only available fully synthetic. The reason is shear stability: an oil meant to behave like a 5 grade in the cold and a 40 grade in the heat has to hold its viscosity across the whole interval. Semi-synthetic oils lose it faster, which shows up as rising oil consumption and a noisier engine.

The filter change goes with it: a 5W-40 works under higher thermal load, and a clogged oil filter eventually opens the bypass valve - and then unfiltered oil runs through the engine.

Frequently asked questions

What is the difference between 5W-30 and 5W-40?

The cold start is the same, the high-temperature viscosity is not: 5W-40 builds a thicker oil film at operating temperature. That helps thermally stressed and older engines but costs a little more internal friction. Which grade is permitted is in the owner's manual.

May I put 5W-40 into a vehicle with a particulate filter?

Only a 5W-40 with a Low SAPS approval, that is ACEA C3 or a manufacturer approval such as MB-Approval 229.51. A classic A3/B4 oil of the same viscosity clogs the filter with ash.

Does 5W-40 help against high oil consumption?

On an engine with wider bearing clearances the thicker oil film can reduce consumption - a well-known effect, but not a repair. And changing grade is only permissible if the manufacturer approves it; otherwise you are treating a symptom and creating a new problem.

Is 5W-40 suitable for winter?

Yes. The 5 before the W describes exactly that cold behaviour and covers a northern European winter. Only in extreme cold combined with mostly short journeys does a 0W oil still give a measurable advantage at start-up.