Entirely off-topic, but in British english the usual term would be combustion vehicle, or more commonly just Petrol/Diesel.

A thermic vehicle sounds delightfully whimsical to my ear, like some sort of victorian steam car.

For some reason the form thermic is almost never used in English, instead preferring Thermal with only one exception I'm aware of: https://en.wikipedia.org/wiki/Thermal_lance