You've made a few small mistakes, but they're non-obvious.

One big thing is that your current vehicle doesn't push the technical mileage limits as far as the Air Car does.

You've assumed the car is the same weight. Cars can be made much lighter than those currently on the market today. You can get well below 1000 pounds. For example, one design prototype is the Volkswagen 1-liter car, which gets 282 mpg. (http://en.wikipedia.org/wiki/Volkswagen_1-litre_car). This design uses a variety of techniques to get the mileage up, and does so quite wonderfully.

With an Air Car it's even easier: you can even do it in a production, mass market system. You need not have a transmission, or an electrical system, or an air conditioning system, so you can get a very good car, a production car, for under 1000 pounds.

Also, unlike gasoline engines, it's a comparatively simple matter to have breaks which recover power. Power recovering breaks become simply a system for compressing and releasing a piston: a fairly mature technology actually. So breaking is not as much of an issue, and the energy you'd lose for it can be recovered at about the 70% efficiency level.

Also, compressed air, at 300 bar (4500 psi) stores approximately 16 kwh per 300 liters, (via wikipedia http://en.wikipedia.org/wiki/Air_vehicle#Storage_Tanks), giving an energy density of 0.0056 of gas (in liters). In other words, gasoline takes 176 times less space, not 3000 times, as you guessed. And given modern tanks, the air is lighter than it is large (compared to gas), though weight is a property of the tank, and does not scale linearly. I haven't factored the efficiency of gas versus air engines into this calculation, as both technologies are varied and evolving.

When these factors combine, you can get a much, much more efficient vehicle than ordinary. Getting around 80 km is a no-brainer, and 300 km is well within the realm of possibility. You might go up to 1000km before you start to hit fundamental limits.

To address some of your other concerns.

The temperature regulation of the compressed air tank is not as much of an issue as you think. There are two temperature regulation problems. The first is heating the tank as you compress it. This is not a fundamental problem, but it's actually a technical detail that I think I've solved, and I want to develop it for my startup. You'll just have to trust me that there's a way to heat this cost effectively. The second direction is when the air is expanding. While the expanding air leaving the tank is quite cold, the tank itself doesn't expand very fast, and air simply doesn't have much heat capacity. Oil and water have a far greater heat capacity, and so running a radiator in a gasoline car is actually a much more significant problem.

Also, the oil they use is actually a vegetable oil derivative. They use a combination anti-oxidant and mineral (anti-corrosion) additive (such as http://www.hexion.com/products/technicaldatasheet.aspx?id=39... though I don't know the exact product).

Additionally, there are wonderful, wonderful ways in which to improve the energy economy of these vehicles as compared to gasoline (or any other comparable vehicle, including electric). Email me, if you might be interested, since I am working on them, and actually looking for more mechanical engineering and organizational talent, or funding, or mentorship.