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Aircooled Engines Overheat at Long Idle?

Discussion in 'Chat & Tech Info' started by Pspice, Mar 16, 2019.

  1. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    Yeah, I agree with the premise. But the Ducati design is not without issues. While the rear cylinder is not shielded by the front cylinder it is shielded by the airbox and intake system. So it is not all puppies and rainbows.
    The front cylinder on the Ducati design runs cooler than the rear, just not as badly as, say, HD.

    A common "add-on" with HD's is an oil temp gauge. It is just a cap for the oil tank that includes a temp sensor and display.
    Also, when an engine runs too hot you can feel it and sometimes hear it. They start to run poorly, and if it gets too bad they start to ping, knock, or detonate.
     
  2. Blaufeld

    Blaufeld Cruisin' Guzzisti

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    Guzzi cylinders protude sideways and are well exposed to air current, just like Douglas Boxer ones, so they don't overheat during runs.
     
  3. Godfrey

    Godfrey High Miler GT Famiglia

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    Actually, the rear cylinder on air-cooled Ducati engines tend to run cooler than the front because the front cylinder's airflow is blocked by the wheel, where the rear gets a straight shot of air being guided in by the rider's legs. I know this by instrumenting both my ancient 750GT and more recent 900SS Ducati engines and watching the temps as I rode in various circumstances. The 900SS (only twenty-five years newer ... :)) was more consistently and evenly warm on both cylinders due to the high-volume oil flow through the heads and oil cooler...

    The main reason to shut down a Guzzi engine when idling (which does not suffer from overheating in any normal running use) is that I if I'm idling at a long long long stop, *I* get hot from the hot air rising off of the engine. :D
     
  4. Kevin Ballowe

    Kevin Ballowe Tuned and Synch'ed

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    Depending on the year, ECU flash, and temperature, many Harleys will shut down the rear cylinder at idle.
    Any increase in the throttle, and the engine returns to firing both cylinders.

    Some owners take this as an over-temp condition and will shut it off to cool.
     
  5. King of Fleece

    King of Fleece Cruisin' Guzzisti GT Famiglia

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    Can you imagine if they ever read the bike's manual? What a concept.
     
  6. Redcad

    Redcad Just got it firing!

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    As H-D engines got bigger, the cooling problems increased. The "watercooled" (exhaust valve only) versions are still a big problem. These fans blow on the cylinder heads and really work;
    IMG_20150630_121611101_HDR.jpg

    I just leave them on from April to October.

    Amazed at how cool my Guzzi stays!
     
    scottmastrocinque likes this.
  7. scottmastrocinque

    scottmastrocinque Scott Mastrocinque GT Famiglia

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    Never seen this before. Thanks for the photo and info!
     
  8. William Horne

    William Horne Just got it firing! GT Famiglia

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    On most of the belt drive air cooled Ducatis the cylinders are oil cooled as well as air. They still run pretty hot though way more heat radiates out when you stop at the lights than on a Guzzi.

    [​IMG]
     
    Last edited: Jul 31, 2019
  9. HarryC

    HarryC Just got it firing!

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    I test rode a Ducati Scrambler before I got my V7. Waves of heat rising off the Ducati Engine when stopped at the lights. I couldn't believe how much cooler the Guzzi was than the Ducati.
     
  10. Chris Wilson

    Chris Wilson Tuned and Synch'ed

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    As per the original post, if any engine is at idle it's throttled to it lowest practical run speed and correspondingly making the least amount of heat for any run condition.
    So very little air flow is needed and generally convection is enough to satisfy all cooling needs.
    The difference with air cooled Vs water cooled engines is that the radiator 'fins' are designed to work only when air is forced through them whereas cylinder fins survive just fine with static air and convection.
    Obviously anything that shrouds an engine dramatically influences heat rejection abilities.
    Water cooled engines benefit is that is evens the heat out much better than air cooled engines, not that they can run cooler.
    Chris.
     
  11. King of Fleece

    King of Fleece Cruisin' Guzzisti GT Famiglia

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    Then what accounts for the closer manufacturing tolerances on water cooled than air cooled?
     
  12. Chris Wilson

    Chris Wilson Tuned and Synch'ed

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    Closer tolerances are possible due to the more even heating (as mentioned above) of the entire engine.
    The more even the heating the less expansion differential between areas and the less you need tolerances.
     
    john zibell likes this.
  13. roadventure

    roadventure High Miler GT Famiglia

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    Yes, this information is provided in the owner's manual.
     
  14. roadventure

    roadventure High Miler GT Famiglia

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    Liquid cooled engines have a more predictable range of operating temperatures and can be cooled in a more even way. Therefore manufacturing tolerances can be tighter because it is known what the operating temperatures will be.
     

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