It was a reply to colb, but...
Flush is an additive. It is a very thin engineering oil (similar to 3-in-1) and has additional detergents in it. It is very good at cleaning a dirty engine. The point I was trying to make is that your engine shouldn't need it.
https://blog.amsoil.com/is-an-engine-flush-good-or-bad/
If it does, it suggests that your engine has not been looked after. If that's the case, the damage may have already been done and the bearing clearances are already out of tolerance. In which case, you may want to use a thicker oil.
As the article says, an engine flush can save an engine, but if the engine is an old rattler, it can be bad for it.
I'd ask myself the question "what am I trying to flush out of the engine"? If you have used poor quality engine oil (an oil that hasn't cleaned the engine as it works), use a flush. My van uses 10W-40 that I can get 20 litres for £40 (£2 per litre). I use a flush on my van as it's not a performance engine (40bhp per litre) and rattles like a tin can.
My Smart car and BMWs have relatively high performance engines (approaching 100bhp per litre) and use Mobil 1 costing £30 for 5 litres (£6 per litre). The oil has enough detergent in it to clean the engine as it works and doesn't need a flush. You can tell this by how clean the engine is under the cam cover.