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Old 04-04-2020, 08:30 AM #1
Morphyne Morphyne is offline
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Knock on start
Ok folks. I've got a head scratcher. I have (what I think is) piston slap on cold start up. After a second, it goes away and it (2005 GX470) runs fine. Actually great. I just cleaned the throttle body, changed the oil and spark plugs bc that's all I know to do to throw at this issue. Any thoughts?
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Old 04-04-2020, 02:45 PM #2
ZLJUANN ZLJUANN is offline
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Without knowing much more than that, it could be a worn rod bearing that’s dry on start up making the noise only on start up.

Any more details?


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Old 04-04-2020, 02:54 PM #3
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Quote:
Originally Posted by Morphyne View Post
Ok folks. I've got a head scratcher. I have (what I think is) piston slap on cold start up. After a second, it goes away and it (2005 GX470) runs fine. Actually great. I just cleaned the throttle body, changed the oil and spark plugs bc that's all I know to do to throw at this issue. Any thoughts?
Sounds more like something rattling (rod bearing) till it gets oil pressure. Not likely piston slap as it will usually take longer to go away than what you describe. Piston slap is pretty common on a lot of newer engines when cold and it usually goes away as the pistons warm up and expand to better fit the cylinders.
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Old 04-04-2020, 05:59 PM #4
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Many with the V8 has describe a knock on cold startup, but many others say it's piston slap and common on the V8 and nothing to worry about.

That being said I have a 2004 V8 and I have never had a knock on cold startup and I have around 200,000 miles on mine....but I'm not sure what most mean when they say "cold", I live in southern South Carolina and we rarely ever have temperatures below 28 degrees or so and even at 32 degrees it's not that often.
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Old 04-04-2020, 07:05 PM #5
Morphyne Morphyne is offline
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Well. I replaced the plugs and oil and cleaned the throttle body and when I started it back up it did it again. But like last time it went away after a second or two. I took it for two healthy test drives and let it sit over night. The next mor NJ ing it started fine. So maybe it just needed some TLC? I can say that the old plugs were rusty and gross and pretty out of spec. Spec is 0.044" and the old plugs ranged from 0.050" - 0.060". So I guess I'll just watch it.
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