Nobody has mentioned the differences in fuel mixtures? (Octane)
Ammunition aside, this rarely happened in WWII and when it did, it took a darn good engineer to either mix up 2 different octanes or add small amounts of various oils or oil products in order to not hinder engine performance.
The BMW 801 for instance, used in 190's, was rated for B4 or C3 octanes only and vehicle fuel lowered engine power by something like 50%.
I'm not totally sure but I think the B4/C3 octanes equal about 110 octane on American planes. Most aircraft fuel of WWII, although very similar to vehicle fuel, still had higher octanes... Up to 150 maybe? So auto engines would burn out super fast if aircraft fuel was used.
Let us also not forget Water Injection engines of WWII. I'm not totally sure they had water injection vehicle engines back in the 40's. And then the Luftwaffe were trying some crazy Methanol-Water Boosting System which kept engines cooler but never gave them the extra power they were looking for. Not to mention the fact that the Luftwaffe had many aircraft engines configured for using synthetic fuels, not natural petroleum fuel.
Now I digress... I dont think there is much modeling going on with the fuels in the game but we all know that the "non-pump" Brit planes will stall when inverted. So I doubt this would make sense if it happened.
Then again, I've been at happy hour for 3 hours today. Maybe a pro can comment on my rantings.
Oh yeah an Ammo for aircraft is belted differently then the .50 cals for vehicles.