Diesel motors and cooking oil

In a nutshell yes, you could use many oils too, automotive oil etc. Though bio-diesel and diesel are far superior for efficiency and reducing issues such as clogged injectors, filter maintenance etc. The viscosity of the cooking oil is the main issue, with many such systems preheating the oil to reduce viscosity, though I suppose you could always start with diesel and then run on oil and run the fuel lines near the exhaust to heat them up [and not too much!]. When oil is converted, it's viscosity is reduced so it's much like diesel and nothing needs to be change within the car to which is the main reason it's done that way. I suppose we could also use lighter oils to bring them closer to diesel.