Can you mix different oil viscosities?

[Ben S3 8P3]

I presume what is in my car now is 5w30. Im about to top the oil up but everyone has advised to use 5w40.

Will mixing these be ok?

Thanks,

Ben

 

[NHN]

Does help if you advise of the year & engine.

 

[Ben S3 8P3]

And also after looking, everywhere seems to advertise 5w40 as turbo diesel oil?

 

[Ben S3 8P3]

Does help if you advise of the year & engine.

Sorry its a 2009 8P3 S3

 

[NHN]

5w30 castrol edge, dont mic viscosities.