1. #31
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    Re: Warming up your car engine in cold weather: yes or no?

    I run a turbocharged car so I wait until the revs drop down to 750rpm before setting off (on first start they sit at 1200rpm).

    Then I let it cool off for a minute when I come to a stop (but my turbo timer does that for me).

  2. #32

    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by Gordo View Post
    PSC, the only scenario where that comes close to making sense is when you're running forged pistons without an internal structure to limit thermal expansion/contraction and/or an alloy with a high rate of thermal expansion (one of the R-R developed alloys in the sixties was bad for this) - and even then the affect is negligible.
    I know you've got at least one healthy beastie there, so I'd remind you that while it's idling there's fuel condensing on the ports and cylinder walls which is diluting the oil film. This is less significant when the vehicle is being driven and there's also more oil being thrown onto the bores, anyway, from the higher rpm.

    Whilst IMO, YOU're incorrect, it doesn't make you a moron, just someone I differ in opinion with.

    All pistons are aluminum be it forged or cast. Aluminum and iron have different expansion and contraction caricteristics (spelling?). aluminum expands and contracts more than iron. I am sure at some point in time you have heard piston slap on a cold morning when an engine has just been started. Thats because the pistons have shrunk so to speak and is rocking in the bore. Start to drive while its doing that and the sound gets louder and faster which is the worst thing you can do. Some engines have tighter tolerances and you dont hear it but its still happening in a lesser degree. Thus you should still warm it up a bit before you drive off.

  3. #33
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by prostreetcamaro View Post
    All pistons are aluminum be it forged or cast. Aluminum and iron have different expansion and contraction caricteristics (spelling?). aluminum expands and contracts more than iron. I am sure at some point in time you have heard piston slap on a cold morning when an engine has just been started. Thats because the pistons have shrunk so to speak and is rocking in the bore. Start to drive while its doing that and the sound gets louder and faster which is the worst thing you can do. Some engines have tighter tolerances and you dont hear it but its still happening in a lesser degree. Thus you should still warm it up a bit before you drive off.
    Sorry, but I still don't agree with you.
    Production pistons, whether forged, cast or eutectic, and many aftermarket forged pistons are made of low expansion alloy and/or designed for reduced expansion (eg slotted skirts) and/or incorporate steel inserts to physically restrain the physical dimensions of the piston. This is to keep cold clearance to a minimum, usually under a thou'. Some older forged designs/alloys could require as much as a thou' per inch of bore and were, indeed, notorious for piston slap even when "warmed up".
    This 'slap' has been further reduced by slightly off-setting the piston pin (gudgeon) from the centre line which greatly eases the transition, although I suspect some are still made "straight up". That's why you need to make sure you keep your 'rods/pistons in the correct orientation when assembling them - esp' when there's a single set of valve notches..
    Whilst it IS damned annoying, this piston slap isn't harmful to the engine and, besides, the piston'll heat up a darned sight faster being driven than idling.
    Then there's still the problem of the enrichened cold fuel mixture causing bore wash from fuel condensing on the port/cylinder walls.

  4. #34
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    Re: Warming up your car engine in cold weather: yes or no?

    Engine block heaters? Hrmm... how much do those cost?

  5. #35
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by Gordo View Post
    Sorry, but I still don't agree with you.
    Production pistons, whether forged, cast or eutectic, and many aftermarket forged pistons are made of low expansion alloy and/or designed for reduced expansion (eg slotted skirts) and/or incorporate steel inserts to physically restrain the physical dimensions of the piston. This is to keep cold clearance to a minimum, usually under a thou'. Some older forged designs/alloys could require as much as a thou' per inch of bore and were, indeed, notorious for piston slap even when "warmed up".
    This 'slap' has been further reduced by slightly off-setting the piston pin (gudgeon) from the centre line which greatly eases the transition, although I suspect some are still made "straight up". That's why you need to make sure you keep your 'rods/pistons in the correct orientation when assembling them - esp' when there's a single set of valve notches..
    Whilst it IS damned annoying, this piston slap isn't harmful to the engine and, besides, the piston'll heat up a darned sight faster being driven than idling.
    Then there's still the problem of the enrichened cold fuel mixture causing bore wash from fuel condensing on the port/cylinder walls.
    Who told you piston slap is not bad? Sorry to say but piston slap is never good, it is if anything neutral but mainly bad. If you use a car while it is cold or rev it up like a mofo you are dumb plain and simple.

  6. #36
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by zstream View Post
    Who told you piston slap is not bad? Sorry to say but piston slap is never good, it is if anything neutral but mainly bad. If you use a car while it is cold or rev it up like a mofo you are dumb plain and simple.
    Piston slap isn't something I seek, I have a preference for tighter tolerances but it isn't BAD for the engine, the loads being relatively light.
    In general, piston slap is due to one of two things, poor piston choice/sloppy build or excessive engine wear.
    Damned if I know where you've got this "rev it up like a mofo" from, we're talking "drive" here which, to me, means light use as it warms up.

    Of all the posts in this thread so far, I'd say yours is the one fitting your last comment best

  7. #37
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    Re: Warming up your car engine in cold weather: yes or no?

    My BMW car manual says never to leave a car idling for excessive periods.You should wait a few econds for the idle to smooth out and then immediatly drive it gently, this warms the engine up quicker with the least wear. If it's really cold idle the engine for a minute, but no more.
    You should also never have both the temperature and fan speed set at the highest setting of your heater, until the water temp is close to running temp.

  8. #38
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by Gordo View Post
    Piston slap isn't something I seek, I have a preference for tighter tolerances but it isn't BAD for the engine, the loads being relatively light.
    In general, piston slap is due to one of two things, poor piston choice/sloppy build or excessive engine wear.
    Damned if I know where you've got this "rev it up like a mofo" from, we're talking "drive" here which, to me, means light use as it warms up.

    Of all the posts in this thread so far, I'd say yours is the one fitting your last comment best
    If you think piston slapping is fine or good then you have a problem. I can not convince you of it because you are hard on the fact it is fine and ok. I disagree and I believe so would a lot of other people.

  9. #39
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by zstream View Post
    If you think piston slapping is fine or good then you have a problem. I can not convince you of it because you are hard on the fact it is fine and ok. I disagree and I believe so would a lot of other people.
    Gordo has the patience of a Buddha when he tries to explain modern engine technology to the uneducated. That's commendable. [thumbup]



    If you always leave the kerb in the style of a bank robber, I'm recommending warming the cold engine first for a few minutes.

    Other people will find it unnecessary as they are capable to keep the load and revs of the engine on a moderate level until the engine and drive train have achieved their normal working temperatures.
    Last edited by BaYegu; September 15, 2006 at 18:33.

  10. #40
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    Re: Warming up your car engine in cold weather: yes or no?

    Quote Originally posted by DT1 View Post
    In really cold weather, yes.

    If it has been sitting for a fair while then all the oil will drain to the lowest point, i.e the sump and you will need to idle the engine draw up the oil to coat the moving parts before you put them under stress.

    The oil is more viscous and less efficient at doing this in colder weather so it is better to warm things up first.

    With modern oils and engines though there isn't much point on your average day, in the time it takes to pull away from the kerb everything is pretty much coated in oil.
    I agree you need to let your engine warm up on cold days. Its not good to just start and go, very hard on a car or truck.

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