For some reason when I searched for "engine+flush" on here, nothing really came up!

Anyway, my mechanic recommends I get my engine flushed prior to an oil and filter change on Thursday. He noticed the oil light stay on for a fraction of a second longer than it should have done on start-up the other day, and says there may be blockages in the engine that a good flush will remove.

I was just wondering what engine flush you guys recommend for astra diesels? And how much would I need?