It sounds like your car overheated because you ran out of motor oil. You said that it was one quart low, but teh dipstick is deceiving in that 2 quarts low actually "looks" like one quart low,,, as does 3 quarts low.

This would also explain the screaming and screatching your poor M617 belched out in protest of no motor oil.

This also explains the top speed of 15 mph (scorched bearings robbing HP.

best bet is compression test and if that's ok look at cam.
otehrwise replace the engine.

Oh Burning vegetable oil most likely did NOT cause this problem.

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