There is other differences between motor fuel grade and aviation Jet A.
The motor grade has something like 128 different things added to it from lubricants for the valves of the production plant, to anti fungals, Then there are additives for combustion flame fronts in the engine etc etc.
Jet A has another load of additives but different ones. If you want to run Jet A in your car stick a couple of quarts of 2 stroke oil in the tank every fill other wise you engine will die after a couple of thousand miles running on it.
As for using motor grade in an aviation engine?
Gawd knows its proberly like most things you will get away with it in a once off get the old girl home requirement. Start using it every fill its going to bite your bum hard.