I don't know about economy, but when I was in college (early 90's) and the Buick had bad bearings - It couldn't hold oil pressure if somebody's life depended on it. The oil pressure light came on anytime under 20 MPH. I poured in a bottle of Slick 50 and drove the car with the oil pressure light on for 2 years until I could afford a new engine. Because the engine had serious problems I really can't say if the FE was impacted, But because the engine didn't lock up on me I had FE...
I suspect that a quality synthetic oil will lubricate your engine better than Slick 50 ever could.
-Jay
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