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I have often heard that diesels are preferred for longer trips and gasoline engines for shorter trips. The reason is probably cost: diesel engine costs more, but the running costs are somewhat lower due to the higher efficiency.

However, if fuel and purchase costs are not a consideration, but longevity and maintenance costs are, which engine type is better for short trips? Let's leave electric cars out of this comparison, as they would be the clear winner.

I can identify at least these factors that favor gasoline for short trips:

  • Gasoline engines don't need occasional long drives for regenerating the particulate filter
  • In cold, using the glow plugs and spinning up the high compression ratio engine uses more electricity, meaning the battery on a diesel car won't necesarily be fully recharged during the short trips

And these factors that favor diesel:

  • If driving short trips, fuel is going to be mixed with the motor oil, and diesel fuel has better lubricating properties than gasoline
  • Diesel engines don't need cold start enrichment like gasoline engines do

Are there any other factors which favor a certain engine type for short drives?

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  • "fuel is going to be mixed with the motor oil" - that shouldn't happen, diesel is not a 2-stroke engine ;)
    – Mark
    Feb 14 '17 at 9:01
  • @Mark on modern diesels with particulate filters that is sadly unavoidable. I have not time for details but the regeneration cycle involves injecting fuel on the exhaust stroke
    – Martin
    Feb 14 '17 at 11:00
  • @Myself I know how it works (in general). We "pump" fuel into exhaust, where it burns, increasing filter temperature. That way we burn most of previously unburn remainings that got to the filter. Some fuel may reach engine oil as the result of other failure (leaking injectors) and some oil might reach combustion chamber (leaking turbo, worn gaskets) but it isn't because of diesel or filter.
    – Mark
    Feb 14 '17 at 11:49
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    @Mark when we "pump" the fuel into the exhaust the injection is after the bdc, so the the diesel aerosol won't get combusted. A part of the diesel aerosol is "wetting" (I do not know a better term) the cylinder walls, diltues the oil film and reaches by this way the engine oil.
    – Martin
    Feb 14 '17 at 12:56
  • @Myself Okay, I agree with you. Still, I don't know why is it in favor of diesel? Need of filter cleanup (and filter itself) is a flaw.
    – Mark
    Feb 14 '17 at 13:12
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Diesel engine is more efficient. That's good, because all the heat produced is more or less wasted (except cabin heating). But despite feeling warm ventilation air later in diesel powered car, that also means that your engine isn't properly warmed up yet.

And because engines are designed to operate best in only certain temperatures (typically around 90 oC) low engine temperature causes faster wear and bigger fuel consumption, reducing advantage of diesel fuel consumption.

You already mentioned particle filter and that's even worse thing. Lower temperature means unburned fuel that covers many parts on the way out and the filter itself. That means costs, costs, costs.

Another thing, not actually related to trip length is environment you are at. Driving through the city means accelerating, braking, accelarating, breaking... Diesel engines are perfect in maintaining speed and handling heavy loads, they speed up slower (that's why almost every diesel engine is equipped with turbo nowadays). But that causes bigger wear on the gearbox, so they introduced dual mass flywheel - yet another thing that will cost you much if broken. And again, urban cycle causes it to wear faster...

So, to sum up - if you drive short trips, especially in the city - go for gasoline. Personally I drive my 1.6 TDCI Ford Focus when going outside the city and 1.3 VVTi Toyota Yaris when going shopping or to the gym.

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The reason is probably cost: diesel engine costs more, but the running costs are somewhat lower due to the higher efficiency.

That reasoning refers to total annual mileage, not the length of individual trips. To give an extreme example: a taxicab makes short trips, it just does lots of them so annual mileage is huge and a diesel makes economic sense.

The short/long trips question is separate from this.

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  • Surely it's to do with the vehicle getting up to temperature. A cab may do short trips but it's in use for several hours so gets up to a good operating temperature. I understood that never getting up to temperature is what kills diesel cars.
    – Steve Matthews
    Feb 14 '17 at 12:55
  • I've clarified my answer.
    – Hobbes
    Feb 14 '17 at 13:08

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