Why are diesel engines more efficient? You know I didn't know the answer to this one, with as long as I have been married to a master certified tech who all he does is talk about cars - okay so I'll give him 85% of the time he's talking about cars - you would think this one would have crossed our conversation. I talked with Jason and asked him why...his response was one that you would expect he started to go on and on. I said I need simple, people are asking, plus after all these years I still don't understand when he starts getting technical on things, or maybe just glassing over. Simply it is because diesel fuel has 30% more energy than gasoline, which makes it more efficient. If you would like more of the technicalities I can get those for you too.