The Best Engine Flush is the one you DONT DO! Here are the results and what the car companies have to say.

Should you Flush your Engine?
Is an Engine Flush worth it?
Are Engine Flushes Good or Bad?
What is the Best Engine Flush?

I tested the 2 top engine oil flushes (Liqui Moly and Sea Foam) on my Duramax Diesel, and the results might surprise you. I used engine oil color to decide which engine flush performed the best. Honestly, I don't think either flush did anything. If the engine is properly maintained and operated under normal conditions, I believe and engine flush is a waste of time and money.

Engine flushes may serve a purpose in some applications, but they can also be harmful. Modern engines have small oil passages in the variable valve timing and displacement on demand systems. If the engine flush does displace an engine deposit, after the oil filter, it could clog a solenoid, valve, or spring, and cause engine damage.

My suggestions is to be cautious with engine flushes, and only use them to correct a contamination issue.

References:

Eric the Car Guy Position:    • Should You Flush Your Engine?  
Chrysler Position: https://www.tsbsearch.com/Chrysler/26...
Ford Motor Company Position:    • Ford Motor Company Position on Chemic...  
GM Position: https://static.nhtsa.gov/odi/tsbs/202...
Honda Position: https://techinfo.honda.com/rjanisis/p...
Hyundai Position: https://www.tsbsearch.com/Hyundai/09...
Do Not Flush TSBs: https://forwardassistmechanics.wordpr...

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00:00 Introduction
01:22 Test Method
06:12 Liqui Moly Flush
08:42 Sea Foam Flush
14:44 Cutting Oil Filters
17:14 Results
19:42 Conclusion