I just flushed both engines -- but with Rydlyme, not BB -- and found no change in engine temps. OTOH, I didn't really expect much change because the engines have been running at the expected temps anyway...
OTOH, I've used another similar product in the past -- from Triton Marine -- on our AC system, and that made a huge difference. I actually bought the Rydlyme this year for another AC flush, and did the engines simply because I could.
Guys on other fora have usually reported good success with all 3 products, depending on their going-in situation on whatever system...
South River, Chesapeake Bay