I also have not seen 10w40 recommend by ford. Only 5w20 and 5w50. Side note: I'm considering using amsoil SS 10w30.......
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2014 Mustang GT w/Trackpack
Competition Auto Dyno 93Race Tune, Flowmaster Outlaw Axle-Back, JLT Oil Separator, Barton Two-Post Shifter, Airaid CAI, BMR LCA w/relocation bracket, SR Performance Adj Panhard Bar, Whiteline Panhard Bar Support Brace, MM camber plates, Koni STR Shocks/Struts, Steeda Ultralight Springs. Future Mods: aluminum Driveshaft, Barton short throw shifter, BMR adj UCA, long tubes/H-Pipe