Cooking oils have poor lubrication properties compared with real engine oil. However, for technical reasosn, some engines tolerate poor oil much better than others.
Small engines, like B&S lawnmowers are designed for use with splash lubrication systems, (no oil pump). They have loose clearances and low stressed parts so they can use poor oil with little short term harm. I remember my dad accidentally mowed his lawn (15 min) with a B&S engine with no oil in it at all - and no harm done.
However, I would guess such an engine would not last as long with veggie oils in it, over the years.
Most motorcycle and ATV engines use roller bearings for the highly stressed parts. Again, such engines tolerate poor oils fairly well.
By comparison, almost all cars and trucks use plain bearings which need a hydrodynamic film of pressurized oil in the bearings to function. Cooking oils shear more easily than real engine oils. If the engine is loaded beyond the shear rate the bearings will be wrecked in short order. So.... don't put veggie oil in your car
