How do diesel engines stay running, if the batteries die and gas engines don't?

My father used to drive a truck and told me that after his engine started, one day his batteries died and (obviously) all the electrical stuff in the truck did too. So, what keeps it running, if the batteries die suddenly? Just curious.

4 Answers

  • 3 months ago
    Favorite Answer

    Diesels with a mechanical pump will keep running as they have no reliance upon electricity at all, apart from starting, and sometimes not even that. There's no electrical ignition system, the engine relying solely on the heat produced by compression to ignite the fuel.  

    These days though modern diesels often have an electric pump and there's also a cut-off held open by electricity which when released will shut under spring pressure and stop the engine.  That's how a modern diesel car, for instance, is shut off simply by turning the key off. That cuts the power to the cut-off valve, it springs shut, the fuel is shut off and the engine stops.  A lot of older engines designs, especially those in trucks, still rely on the driver physically cutting the fuel by pulling on a knob or lever.

  • 3 months ago

    Because the diesel ignites the fuel from heat and high compression while gas motors need spark to ignite the gasoline.

  • Anonymous
    3 months ago

    You are talking about older diesel engines.  They do not need electrical power to run once they are started.  The injectors and injection pump are mechanically powered and controlled.  On new modern common rail diesels with an ECU, electrical power is needed to run the ECU.  Without power to the ECU, the engine dies.

  • 3 months ago

    You just have to keep it charged

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