To be honest I do use engine flush like once every 2nd or 3rd OCI, never had a problem and my engines always running relatively clean but I also use trusted good oils and never had bad sludge build up, so the whatever minor gunk removed must have been disolved well without clogging elsewhere.

The engine flush I used was like a thin oil cleaner which still has lubricating properties, bought in Ace Hardware, forgot the brand but made in USA and sold in a clear plastic bottle so can see how the liquid is.

Actually can just use some cheap mineral oil, that's what I used to do. I drained the old oil, filled up with new cheap mineral oil plus an engine flush, idle it for 30 mins. Drained it again then would see how dirty that new oil became. Then I even refilled again with the cheap oil, idle for 15 mins and drained it again. By then usually the drained oil already golden clean. Then only I put a new filter and the real oil I want to use. But now lazy already so I don't do that anymore.

This post has been edited by 6UE5T: Sep 13 2021, 12:28 PM

Hmm running for a week using cheap unknown oil is risky IMHO. You need to use at least trusted brand oil within the range of viscosity for your engine.