Why the USA/UK split in naming motor fuel? We in the USA say "petroleum" for the unprocessed product, but don't carry through with the name. A bit odd, no?

Asa, who confesses to being a bit odd due to having sniffed waaaay too much of it!

Well before the automobile the word 'gasoline' was used for certain petroleum derivative (I think for the same one we now call by that name). 'Petrol' was a much older word, but it meant petroleum, not what GB calls 'petrol' for the car.

But at the motor car era (and perhaps before) the French apparently called that fuel essence de pétrol. OED says it came into English "c1893 by Carless, Capel and Leonard Ltd., oil refiners in Hackney Wick, who were working for F. Simms and through him for Daimler (cf. quot. 18952 at sense 3). An attempt to trademark the term failed."

I think it very likely that it came from the French along with a lot of other automotive terms e.g. chassis, chauffeur, garage, etc.

Do a lot of our words about cars come from the French? If so, that's interesting because Asa has said that a lot of airplane words come from them as well.

Yes, the French contributed a lot to mechanical nomenclature. Indeed, while the Germans produced the first internal combustion engine powered automobile, a Frenchman named Cugnot built a steam powered artillery carriage about a century before Daimler and Benz "invented" the automobile.http://www.history.rochester.edu/steam/brown/chpt5.html

The French and Germans were the first to sell motor cars and engines and most British manufacturers started by buying a Continental engine and putting it into a frame or chassis. Such engines had capacities denoted in cubic centimetres which is why, in our staunchly Imperial country, our cars and bikes are categorised by the capacity in metric units.

In the USA, where French and German motors were not so common, the indigineous manufacturers denoted their capacities in cubic inches. Which is why, to this day, the USA capacity categorisation for cars is different from most (all?) other countries.