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Engine knock when cold

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Old 10-08-2006, 08:00 PM
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rick229
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Default Engine knock when cold

Lately I have been hearing a knock in the engine when it is cold. This only happens after the car has sat overnight. The knock goes away after 2-3 min. My car is an 05 with just over 17,000 miles. The oil has been changed 4 times at 3500-4000 mile intervals. Anyone else having this problem please respond. Rick.
Old 10-08-2006, 08:18 PM
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VET4LES
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Could be lifters which is normal but 2 or 3 minuets is to long for that. If it is really that long you should take it to the dealer and have it checked.
Old 10-08-2006, 08:20 PM
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Wayne O
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Assuming you use premium, high octane fuel....I would also suggest having the dealer look at it. It might just need the PCM re-flashed to factory specs.
Old 10-08-2006, 10:35 PM
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Mr. Lucky
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On a low mileage, well maintained vehicle like yours, I doubt that it is actually engine knock that you are hearing. The stock oil filter has great filtration properties, but has very poor flow characteristics. I think what you are hearing is "normal" cold start valvetrain noise, caused by the low flow. It goes away after the engine oil warms up.

At your next oil change, instead of the stock Delco, try a Baldwin B31 or a K&N HP-1007 filter instead. Unless you are actually unlucky enough to have real knock, I'll bet the noise will be gone.
Old 10-09-2006, 12:42 AM
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Piston slap?? Have to leave it at the dealer overnight for a diagnosis. Big problem with the LS1s.
Old 10-09-2006, 07:16 AM
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The service manual says you may need an oil filter with anti-drain back, so I would have to agree with Mr. Lucky

I dunno about which filter has that ability; I use Mobile 1 filters (M107) and no start up noise. When I use AC Delco, I get the lifter/rocker noise

Last edited by AutoCutter; 10-09-2006 at 07:18 AM.
Old 10-09-2006, 07:19 AM
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rick229
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Thanks for the replies. I am going to try a different oil filter and put a magnetic drain plug in and see if there is any metal in the oil. I hope that is just low oil flow when cold. Thanks again. Rick (save the wave)
Old 10-09-2006, 09:36 AM
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Originally Posted by Whiteonrice
Piston slap?? Have to leave it at the dealer overnight for a diagnosis. Big problem with the LS1s.
I agree 10000%...Piston slap...a long time trademarke of the Corvette...Don't waste any time trying to get this fixed...does no damage and will always be there!!!
Old 10-10-2006, 05:22 AM
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Gearhead Jim
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Originally Posted by srpbaer
I agree 10000%...Piston slap...a long time trademarke of the Corvette...Don't waste any time trying to get this fixed...does no damage and will always be there!!!
Yep, our C5 sounded like a diesel for the first 2-3 minutes after startup, then fine after that.
Old 10-10-2006, 07:54 AM
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Z06 Steve
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Originally Posted by Mr. Lucky
On a low mileage, well maintained vehicle like yours, I doubt that it is actually engine knock that you are hearing. The stock oil filter has great filtration properties, but has very poor flow characteristics. I think what you are hearing is "normal" cold start valvetrain noise, caused by the low flow. It goes away after the engine oil warms up.

At your next oil change, instead of the stock Delco, try a Baldwin B31 or a K&N HP-1007 filter instead. Unless you are actually unlucky enough to have real knock, I'll bet the noise will be gone.
yes its true try and see

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