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I have always had gasoline cars, for which it appears (based on advice from other motorists and from fuel consumption meter), that it is advisable in general to run them between 1500-2000rpm.

Going above 2100-2200 for longer periods seems to increase fuel consumption significantly regardless of speed/transmission and rpm of around 1500-1800 seems to be what should I aim at.

Now I have bought a 2005 Honda CR-V 2.2 CTDi turbodiesel, and I have been told by a CR-V enthusiast, that I should in general aim to stay around 2000-2500rpms, for best fuel consumption and for longer engine life, as staying in this range would be better for dealing with exhaust gas recirculation and soot filters.

Is it true in general, or could it be true for this specific engine/car? Also, is my initial presumption about gasoline engines correct?

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  • You mean high speed Diesels; low speed diesels run a few hundred RPM.
    – blacksmith37
    Oct 4, 2021 at 18:21

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A bit of googling suggests that the CTDi does not have a DPF (Diesel Particulate Filter) - it's these that need a regular run at a high, constant RPM to burn off the buildup of soot.

Otherwise, in general Diesel cars run at a lower RPM than petrol cars, as peak torque is lower for a Diesel engine than a petrol one. For example, for my car, the petrol version has a peak of 170NM @ 4200RPM, wheras the Diesel is 280NM @ 2000RPM

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Usually, the answer is no, although the specifics depend on the exact engine pair you're comparing.

Diesels cannot run at high RPMs due to low fuel burn rate, whereas gasoline engines can.

Because the redline of diesel engines is lower, the parameters of the engine are typically optimized for running at these lower RPMs. So, if you're looking at a diesel engine, chances are it's optimized for running at low RPMs, whereas a typical gasoline engine (for "high maximum power" marketing reasons) may very well be optimized for running closer to its maximum RPM to achieve high maximum power.

Some technologies like VVT (ideally dual VVT, on both intake and exhaust) and two cam profiles like in VTEC or variable valve lift may allow tuning a gasoline engine to run smoothly from 1000 RPM to over 6500 RPM.

Many diesel engines can very well run at 1200 - 1500 RPM, perhaps even 1000 - 1200 RPM. Note diesel engines run a bit rougher than equivalent gasoline engines.

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  • While I think that this is a good response, I don't think that looking at peak power or torque curves is the right approach for this problem, which is more concerned with BSFC. Gasoline engines being more "peaky" as a consequence of marketing numbers is also not a bulletproof argument, as good fuel economy and early, punchy torque are both important too - especially for standard, non-sport models.
    – Kitsunemimi
    Mar 8, 2019 at 17:21
  • Thank you for the information. I am wondering if this works with Honda owners' forum info where somebody says: If I'm not mistaken, the Cr-v has always been designed to burn less fuel aat higher RPMs. Lugging the engine will cause you to lose MPG. crvownersclub.com/forums/76-fuel-economy-gas-related-discussion/…
    – Gnudiff
    Mar 8, 2019 at 17:56
  • What you don't want to do is lug the engine if it's a diesel like you would in a gasoline vehicle with a manual transmission. Diesel engine efficiency drops off above about 70% torque load, and the black soot that starts coming out the exhaust is unburnt fuel that is wasting your money.
    – Alex Cannon
    Oct 5, 2021 at 16:07

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