cold knock, normal?
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This is a discussion on cold knock, normal? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Seems I have a very quiet knock while cold and it goes away in 10 or so minuets once the ...

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    Registered User jquicksilver008's Avatar
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    cold knock, normal?

    Seems I have a very quiet knock while cold and it goes away in 10 or so minuets once the car fully warms up.

    There are no CELs and I have 80k+ miles, the car drives otherwise perfect, would changing the oil to 10w30 instead of 5w30 help?

    Thanks

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    Registered User WRX13oy's Avatar
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    seems like it could be piston slap? i know engines with forged pistons tend to have piston slap till they warm up. hmm
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    He simply abides. SD_GR's Avatar
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    Quote Originally Posted by jquicksilver008
    Seems I have a very quiet knock while cold and it goes away in 10 or so minuets once the car fully warms up.

    There are no CELs and I have 80k+ miles, the car drives otherwise perfect, would changing the oil to 10w30 instead of 5w30 help?

    Thanks
    Sounds like piston slap. Do a search for the term and you will find horror stories (some by me...) with happy endings. Though it sounds absolutely revolting and it makes me sick to think something like this would be allowed to happen, it does and nobody's had any problems with it other than having to listen to that crap go on. Mine does it too if that helps; check around for a post I did a while back (40k miles ago...) on oil analysis data from my motor. It was basically pristine at 30K miles on the clock, with the pistons slapping away the very day I collected the oil sample and ever since.

    Switching to a 10W-30 will not likely help. The first number designates the oil's behaviour during cold startup, and a 5W is more likely to flow better during low exernal temps and/or cold startups than a corresponding 10W (I'm generalizing). I have used 5W-40 and now 0W-40 Mobil 1 and still get slap; theoretically, the 0W-40 is good from the arctic circle to Mauritania.
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    Registered User Robert46123's Avatar
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    +2 on the piston slap. My '02 did it from nearly new and was doing it when I traded it in. It's really more annoying than anything else, and the car will be fine. My '06 has yet to devolop it, but it's got that annoying wastegate flutter. Consider it part of the Subaru experience.
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    Registered User jquicksilver008's Avatar
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    Cool, thanks for the help !

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    Registered User rlem00's Avatar
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    I've got the same sound at start up and until a couple of days ago had just kinda expected it...then 60k service, changed plugs and fuel filter on saturday, first start up and no knock?? Two more days and no knock?? I have not had a chance to post anything about it but found it odd, my old plugs were the stockers and worn but nothing to scoff at for 60k. I switched to NGK 1 step colder gapped at .030. I'm sure it will come back but if the plugs did it, may be worth a try??
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