These types of engines are much noisier than the petrol ones because their mechanics work under higher pressure. There are a lot of small parts inside, such as metal caps, small valves and oil pipes, that create the noise.
Over the long haul, newer diesel engines will last 15-20 years in a fleet, while a gasoline engine may need to be replaced once or even twice during the life of a school bus. “All of these are important for fleet managers to stop and consider when choosing a new school bus,” says Hedgecock.