Short answer
5W-40 shares the same cold rating as 5W-30, so cold-start flow is similar — but it is thicker at operating temperature. That makes it a conditional choice rather than a drop-in replacement. It is reasonable where your owner’s manual or the European specification it references lists 5W-40; for an engine that calls only for 5W-30, the thicker grade is not recommended.
Many European manufacturers write their oil requirements around specifications (for example ACEA or specific OEM approvals) that are commonly met by 5W-40. If your manual points to such a spec, a 5W-40 that carries that exact approval is appropriate. If your manual lists only 5W-30, going thicker without that backing is a deviation from the engine’s design.
Why it depends on your manual
The shared 5W rating means you are not giving up cold-start performance, which removes one common concern. The difference is the hot grade: 5W-40 leaves a thicker film at temperature than 5W-30. For some engines and specifications that is exactly what the manufacturer intends; for others it is more than the clearances and oil-pump output were tuned for.
Because going one step thicker is a nuanced case rather than an outright hazard, this is a check-your-manual answer. Where the manual or its referenced European spec sanctions 5W-40, use it with confidence. Where it does not, stay with 5W-30 to keep within the design window and protect any warranty or emissions claim.
If you are unsure, match the exact specification printed in your manual, or ask a trusted mechanic about your engine, climate, and how you drive.