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My 2.7 knocks when it's very cold for a minute or so after start-up. If I don't let it warm up and drive right away it knocks a lot. This is no big deal, I just let it warm up, but what is the theory behind the cold knocking? Yea yea I know some smart-ass is going to say run leaded fuel to fix it :rolleyes:
 

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TacoDude,

I don't know if it's something to worry about or not, but my 2.7 does the same thing. I don't think it has anything to do with oil, if that is your question. Mine does the same with new and old oil and I always run the same gas. It just does it in cold weather.
 

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Mine does too. There have been many topics on this and it is said to be normal.
 

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Discussion Starter · #5 ·
It might be piston slap. I was told a while ago that piston slap is harmless but apparently it's not, and there's even been a big lawsuit filed against GM because of it.
 

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yeah u dont want misfires, my dad just shot the motor in his vette, becuz of the piston slapping, but this was due to the lack of octane it required, its prb has something to do with the BTU factor in the fuel, colder the engine = lack of combustion
 

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Yea it been like -20 degrees here for like 2 weeks now and mine does it i just let it run for at least 5 min before i will drive it..
 

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Mine started knocking the next morning (5:30am) after I changed the oil, it was 32 degrees outside, it has not done it since, but also has not been that cold again either, if it does it again I`m going to change my grade of oil to something thinner or synthetic.
 

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tanKoma said:
yeah u dont want misfires, my dad just shot the motor in his vette, becuz of the piston slapping, but this was due to the lack of octane it required, its prb has something to do with the BTU factor in the fuel, colder the engine = lack of combustion
Bullshit. Piston slap has nothing to do with fuel or octane, that is knock, ping or detonation. Piston slap is purely related to mechnical dimensions, heat and expansion.
 

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You need to try a different brand oil filter, one with anti flow valve. I think you can go to Advance Auto Parts and get a Purolator for about $8, this is the best filter you can put on your truck IMO. Others make oil filters with Anti Flow valve, some are low quality and leak down, this allows all oil to return to pan, causing a dry start. If you try the filter and it doesnt work, try some Lucas oil additive, this stuff works great.
 

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Thinner may or may not help, sometimes thicker oil clings to parts better, and doesnt drain to the pan, like thinner oil, most likely its the anti flow back valve in a cheap filter that causes knock when first starting. All my Toyotas and Hondas would knock with cheap filters, OEM or better filters always stopped knock.
 

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2.7 knock

How many miles are on these knocking 2.7?
 

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Since 30K miles I have the exact cold start piston slap sound on my 3.4 V6 (34,000 miles). Nothing but dealership oil/filter changes @ 3K or less. Drives me crazy hearing that sound, along with my valve train noise 3K rpm. Only time will tell is piston slap is bad for engine life. I do wonder what Toyota is thinking, whether they try to make noisy engines with no sound isolation just to remind us that we've got an engine (tongue and cheek)?
 

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My 95 with 210,000 miles does it and it has gotten worse sense I've owned it. I've tried different filters, additives like Lucas, and Risolene, they help some for a little while but not for long. Everyone says its pitson slap, all I know is its annoying and embarrassing when is sounds like an old model T in the mornings. Consensus a while back seemed to be just live with it.
 

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some one told me it was a crack in the header. Im not sure if its true but i dont have the money to buy a new header from LCE to find out. Has any one else heard of this.?
 

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It's ok guys, the piston slap is caused by the different heat expansion rates of aluminum and iron. The engineers have bored our cylinders to accomodate the expansion rates of the moving parts to where when the engine is at operating temp all the tolerances are dead on. Until things are at operating temp the piston skirts will slap a little causing the noise you hear; it is harmless. However I do suggest letting things warm up a few minutes before heading out on cold mornings; and this was advised long before they used aluminum in engines.
 

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However I do suggest letting things warm up a few minutes before heading out on cold mornings; and this was advised long before they used aluminum in engines.[/QUOTE said:
Since it only occures durring very cold weather, couldn't it be avoided by installing some sort of preheater. I don't know anything about them (live in Fl.) but I'd like to learn about how they work, what they cost, and how they're installed.
 

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A coolant heater may help; I have used them when stationed up North and they work well. The heater is even ready to blow warm air when you start it up.
 

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John Luttrell said:
It's ok guys, the piston slap is caused by the different heat expansion rates of aluminum and iron. The engineers have bored our cylinders to accomodate the expansion rates of the moving parts to where when the engine is at operating temp all the tolerances are dead on. Until things are at operating temp the piston skirts will slap a little causing the noise you hear; it is harmless. However I do suggest letting things warm up a few minutes before heading out on cold mornings; and this was advised long before they used aluminum in engines.
I don't think it's piston slap. If it were, then the rate would increase with engine RPMs, correct? Mine goes away when I rev it. I've been told its somehting in the valve train. Either way, doesn't matter. Owners, dealers and Toyota agree, its normal.
 

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Eztrog88 said:
I don't think it's piston slap. If it were, then the rate would increase with engine RPMs, correct? Mine goes away when I rev it. I've been told its somehting in the valve train. Either way, doesn't matter. Owners, dealers and Toyota agree, its normal.
Actually, if you rev it, then it heats up faster and the oil will rise and the aluminum will expand, making the noise go away. Piston Slap only does it for a few seconds on most cars until it heats up, which in your case, you seem to make it go away by reving it up.
I have the same problem and I am finding out what the experts are saying: it is not normal and it is the beginning of your engine problem. Ford and Chrysler did a recall and they're replacing thousands of engines while GM is not.
Many toyota truck owners are concerned with this problem so we're gathering up some data and see if toyota is still willing to say that it is normal and a rare case.
 
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