My experience is it’s worth taking it off for a specific reason - it holds a lot of heat in the engine. So mine comes off for race season and back on for winter. Same thing with the under-engine tray/cover. Really protects the engine bay from winter road debris and salt spray but holds a lot of engine bay heat in the warm weather.As much as I love to see my engine, I'm happy to take a hit in performance that's so small you can't measure it, in order to cover that mess of wiring and piping in these cars.
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Have you done any proper testing on that? As metroplex said, nearly all, if not all vehicles nowadays, use the shielding to a help cooling as well, by directing air under the body to other parts. The Jaguar F-Pace is one thing I know (just due to my own interest in those) has shown much warmer trans & diff temps without the shields on. Ice also owned 2 MK3 Eacape's, same deal with those. I've never tested on the Fusion to be sure tho, but I'd be very surprised if that wasn't also the case.Same thing with the under-engine tray/cover. Really protects the engine bay from winter road debris and salt spray but holds a lot of engine bay heat in the warm weather.