The Edinburgh University student hit upon the culinary brainwave after sitting outside a service station facing a range of unappetising dinner options.
Now he cooks up everything from sirloin steaks to pigeon by wrapping ingredients in tin foil, placing it under the bonnet and setting off on road trip.
And his creations are being published in a new cook book, Carbecue.
Mr Cary said: “Sitting in the service station got me thinking; there must be a better way, a way to eat delicious hot food, on the move, at your convenience.
“This triggered the idea that cooking in its simplest form was just applying heat to food. Where could you get heat from? A car engine.”
The first recipe he tried was on a long distance drive involving lamb chops, potatoes and green beans. He wrapped them up in tinfoil and put them on the engine before setting off.
“I don’t think I have ever been so excited about a meal,” he said. “About 100 miles down the road we stopped for lunch and unwrapped the piping hot package with nervous excitement. Inside were beautifully cooked lamb chops with steam billowing out.
“It made for such a jolly lunch. We ate and started thinking about what we would cook next.”
The student, originally from Henley-on-Thames, has now cooked 100 different recipes on various cars . . . and only messed up twice.
Cooking on car engines is a mostly American phenomenon and popular among truckers eager to serve up a hot meal without paying for electricity to heat their ovens.
And for Mr Cary, a love of food is a family affair. His sister, Lettice, is a freelance chef while brother Horatio is an engineer for a food company.
His sister has even helped compile his new book.
The madcap author said meals can be cooked on any petrol or diesel car engine – but not electric cars which don’t produce enough heat.
“I advocate that you should never drive to cook but only cook when driving,” he said. “If you are doing a journey anyway then it is highly likely that en route or on arrival you may want to eat. In this case it is sensible and sustainable to cook using your car engine.”