One of my reasons for buying a diesel was environmental -- I thought it would damage the planet less. It seems I was mistaken. But could a diesel engine be converted to petrol (gasoline)? Obviously this is not a home project, but as far as I understand it, for a reasonably modern (post-2000) diesel you would need:

  • new cylinder head (spark plugs and lower compression)
  • new wiring for the spark generation and distribution
  • new software in the engine control systems
  • (maybe) different cam profiles (not too tricky if you're fitting a new head)
  • You might need different gasket/filter materials in the fuel pumps and injectors

... which doesn't sound like too much. The engine would be overweight and thus sub-optimal, but you would avoid the problem of disposing of millions of old diesel vehicles. In general, are there serious problems in converting diesel to petrol?

  • Different fuel pump(s) and injectors - pressures are a lot different...
    – Solar Mike
    Mar 9, 2019 at 23:25
  • 3
    Realistically, if you want to change from diesel to gasoline, you'd need to either swap the engine (and other running bits) wholesale, or just sell this car and get a different one. There's really no easy way to do it. Mar 9, 2019 at 23:34
  • The petrol engine also needs a different trottle valve and, though technically not necessary, a cat. Modern diesels all have turbos, but those don't have to cope with the very hot exhaust gas of a petrol engine. Remove or exchange it. And what about the gearbox? Diesels run slower than petrols. When you finally changed everything, what's the milage?
    – sweber
    Mar 10, 2019 at 10:17
  • 1
    Apart from all the alternatives suggested you may also convert your car to an electric vehicle if you are so prone to keeping it. It may be a better investment if you are consedering something as big as an engine swap. There are some DYI convertion guides online and there are some people really excited about the whole thing. There were also a cult of people running their diesel engines on vegatable oil. It sounds sketchy but it has been around for few years. Maybe there is some hidden genius to the whole thing. (Most likely it is nonsense) Mar 10, 2019 at 18:17
  • @sweber so gas engines have very hot exhaust - and what about diesel? Does slower mean cooler?
    – Solar Mike
    Mar 10, 2019 at 20:22

1 Answer 1


Diesel engines are more efficient than petrol engines. Today's diesel-powered cars have to comply with the same emissions standards as petrol-powered cars. Don't let headlines sway your outlook. Volkswagen/Audi put fuel economy and horsepower ahead of nitrosoxide emissions and paid dearly for it. Enviornmental issues today are clouded in politics and the almighty dollar.

  • No, the emission standards are not the same. Petrol may emit more CO, diesel may emit more NOx. The low emissions and efficiency comes with a cost (on a diesel, at least): diesel engines contain more high-tech parts that are expensive to repair.
    – juhist
    Mar 10, 2019 at 17:50

Not the answer you're looking for? Browse other questions tagged or ask your own question.