Can You Drive A Diesel Truck Or SUV Even When Its Engine Is Underwater?

Americans may not be too fond of diesel engines, but that doesn't mean they're any less vital for the economy than their gasoline-fueled counterparts. For example, in 2022, the U.S. transportation industry consumed roughly 125 million gallons of diesel fuel per day. Meanwhile, the U.S. military uses ground vehicles with diesel engines because they are more durable and less likely to stall than gas engines, and diesel fuel is less flammable in open air than gasoline.

Despite this, some myths about diesel engines persist. One of the most dangerous is the myth that you can drive a diesel truck or SUV even when its engine is underwater. It is unclear where this myth originates from, but one could speculate that it has something to do with Hollywood portrayals of military vehicles, which often show trucks and tanks powering through deep water with ease. The real reason military vehicles can run when submerged in water has very little to do with their engines, but a lot to do with the modifications made to them.

While there are different types of internal combustion engines, none of them work underwater. In order to run properly, a combustion engine needs a source of intake air and a way to release exhaust gases. Obviously, this is impossible when a vehicle and its engine are submerged underwater. So, how does the military solve this problem? Military vehicles that operate in water are equipped with snorkels. Humvees, for example, have snorkels that allow them to them to ford up to 5 feet of water. The snorkel allows the engine to draw in air from above the water's surface while the vehicle stays partially submerged — this is pretty much how diesel submarine engines work underwater. 

But snorkels are just one piece of the puzzle. The engine and the entire vehicle would need to be waterproof for it to operate under water. Instruments, motors, lights, differentials, doors, the fuel tank, and other components all must be sealed to prevent damage. Unlike gasoline-powered engines, diesel engines do not use spark plugs or a traditional spark-based ignition system, so they are a little easier to waterproof. In theory, you could drive your truck or SUV through water, but it would have to be heavily modified to the point of becoming a specialized vehicle and potentially unregisterable, regardless of whether it has a diesel engine or not.