Car manuals say: "Don't let your engine run idle for long"

Discussion in 'The Garage' started by AstroGuardian, Sep 21, 2010.

  1. AstroGuardian

    AstroGuardian Senior member

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    I was reading my Chevy Spark's user manual when i came across this:
    "Don't allow the engine to idle for long"
    But it does not say for HOW long... And frankly, why not? It doesn't say the reason also.
    I have read this about Skoda, Ford and Folkswagen but none of them writes as to why should't i leave the engine to idle.

    Anyone has an idea? I mean from technical point of view aside for CO2 emission, fuel consumption or so...
     
  2. JCH13

    JCH13 Diamond Member

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    Idling gets more fuel in your engine oil than running the engine under load. Fuel in your oil screws up the oil's viscosity and ability to lubricate your engine. Bad news.
     
  3. skyking

    skyking Lifer

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    ^ all that, plus the exhaust system is too cool, etc. The powertrain is not designed to idle for long periods of time. It is designed for a median amount of work.
     
  4. Bignate603

    Bignate603 Lifer

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    There's no point where it's suddenly damaging, like 5, 10, or 20 minutes. It's more of cumulative problem over the life of the car. The only immediate thing that you might run into is overheating, especially if you're running accessories like the AC.
     
  5. darkswordsman17

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    Also, idling is one of the worst things in regards to efficiency as no work is being accomplished so its usually fairly wasteful. Plus, I've actually seen people complain about how few miles they get out of a tank of gas and come to find out, they let their car idle a lot.
     
  6. DivideBYZero

    DivideBYZero Lifer

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    The manuals focus is emmisions and fuel consumption.
     
  7. WhoBeDaPlaya

    WhoBeDaPlaya Diamond Member

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    I usually let my car idle for 3-5 mins in the mornings and after work, then drive it easy for the first couple of miles.
     
  8. HarryLui

    HarryLui Golden Member

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    Idling your car is a waste of gas when the engine is in its operation temperature.
     
  9. amdhunter

    amdhunter Lifer

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    Pollution and emissions more than anything else I bet.
     
  10. mb

    mb Lifer

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    Unless you do that with a remote starter to cool/heat your car, that is 100% pointless.
     
  11. AstroManLuca

    AstroManLuca Lifer

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    On the other hand, you shouldn't stop and start your car too much either. I made that mistake while waiting in line for a car wash. Rather than idling for ~3 minutes while each car ahead of me got washed, I just shut the engine off. Third or fourth time, the car wouldn't start. Luckily it did eventually start after it sat around for a few minutes. Scared me though.
     
  12. JulesMaximus

    JulesMaximus No Lifer

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    There is really zero need to do that. Unless it is brutally cold outside you can safely drive off within 10-15 seconds after starting the engine. Just don't romp on it until it is up to normal operating temperature.
     
  13. exar333

    exar333 Diamond Member

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    The only time I let my car idle is to warm it up in the winter; sub-zero temps don't agree with vehicles to well (assuming it is left outside). Usually 3-5 minutes is plenty.
     
  14. JCH13

    JCH13 Diamond Member

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    Exactly. Your engine warms up faster under a light load anyway.

    This too, otherwise the transmission fluid feels like sludge and makes shifting a bitch.
     
  15. thescreensavers

    thescreensavers Diamond Member

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    hmm, dont trunks idle for hours on end?

    I never heard about idleing causing issues :O, what about people who sit in a drive through?
     
  16. Vette73

    Vette73 Lifer

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    Leting your car idel use to be bad when cars came with Carbs and they dumped to much fuel in. With FuelInjection it is not really an issue anymore. Waste gas; but should not damage the engine.
     
    #16 Vette73, Sep 21, 2010
    Last edited: Sep 21, 2010
  17. JCH13

    JCH13 Diamond Member

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    Blackstone oil testers frequently link excessive idling (even lots of stop-and-go) to abnormally high levels of fuel in the oil, at least from what I've read. Granted it would take a bit of gas to cause immediate damage, cumulative effects will be bad.
     
  18. AstroGuardian

    AstroGuardian Senior member

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    What you say here mate IMO is contrary to logic. If the engine idles there is minimal stress to the piston rings and therefore minimal chance that a fuel would pass through and mix with the oil. I don't understand how would fuel mix with oil?
     
  19. AstroGuardian

    AstroGuardian Senior member

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    Sorry i forgot to mention that it is a manual transmission vehicle which means that when in neutral there is zero stress to the transmission...

    Why do you say that the powertrain is not designed to idle? I mean a machine is machine, it should work better with less stress than with more stress...

    What does exhaust system temperature have to do with anything?
     
  20. AstroGuardian

    AstroGuardian Senior member

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    This is the most logical explanation by far. let's say that the AC is not on (i rarely use it).
    Overheating should not happen even with AC turned on. In one occasion after climbing a mountain road for a whole hour i left the engine to idle a bit in order to cool off. I forgot it for at least 45 minutes. The temperature was only 85c and the cooling fan was off.

    I didn't mention that it is a 0,8L three cylinder engine with 55 horsepower and 75nm torque...
    I know you Americans will laugh... but at least i get 65mpg in Europe (autobahn) :)
     
  21. AstroGuardian

    AstroGuardian Senior member

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    Whatever anyone says that's a smart thing to do especially during cold winter mornings. The oil does not lubricate the engine and transmission before it's heated up to at least 5c.
    That's why the Germans tanks lost the war in Russia during second world war cause their oil froze and mutilated their engines ;)
     
    #21 AstroGuardian, Sep 21, 2010
    Last edited: Sep 21, 2010
  22. AstroGuardian

    AstroGuardian Senior member

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    I am only guessing that there might be less oil pressure during low RPM and therefore less lubrication. But i have seen the engine valves (i don't know the english terminology for this. Actually i peeked through the oil cap on the top of the engine and all visible parts are juicy lubricated even during cold start) and they were all lubricated.

    What is you opinion on this?
     
  23. JCH13

    JCH13 Diamond Member

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    This happens for a couple of reasons that I am aware of:

    1) Piston speed is low, so there is a longer time for air/fuel mixture to slip past the piston ring.

    2) Timing is retarded, so again there is a longer amount of time that there is unburnt fuel in the cylinder, and therefore more time for it to slip past.

    3) Idle is generally at a very low MAP (manifold absolute pressure) and your PCV (positive crankcase vent) brings the crank case pressure down very low. This creates a larger pressure difference across the piston rings, which results in more air/fuel being pushed across the piston rings.

    Does that make sense?

    The stress that piston rings see (I believe) are not large enough to create significantly more leakage.
     
  24. mb

    mb Lifer

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    Incorrect.

    Maybe a full minute or two on those super cold mornings (or however long it takes for the interior to warm up anyway), but for the other 360 days of the year, it is not needed. By the time you buckle your seat belt and release your parking brake (if applied), you're good to go.

    Next you'll be telling us we need to inflate our tires to sidewall.
     
    #24 mb, Sep 21, 2010
    Last edited: Sep 21, 2010
  25. AstroManLuca

    AstroManLuca Lifer

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    How cold is "super cold"? Should you let your car warm up for a few minutes when it's below 15? Below zero? If you live in California you may never have to let your car warm up but if you're in Minnesota or Michigan there are a few months of very cold weather every year.