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Old 01-08-2011, 07:48 PM
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Rod Knock When Cold

I have a Toyota Corolla with over 200K miles that runs good. It does use about a 1/2 qt of oil with every fill up, so I use thicker oil to reduce the consumption. I use 1/2 10W40 and 1/2 20W50 oil. On these really cold mornings I hear a little bearing knock from one cylinder until the engine is warmed up. It is perfectly quiet then.
Of course with the thicker oil than the recommended 5w30, the oil will be a little slower moving thru the engine, but I believe there will be enough oil in the bearings to provide lubrication plus the thicker oil will not leak out from the bearing as fast.

Why do you think there is noise when very cold?

With the high mileage the bearing clearance should not be so tight to restrict oil flow, and the pump should be able to circulate oil thru them. i will install a mechanical oil pressure gauge to see how the pressure is.
thanks.

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Old 01-08-2011, 07:57 PM
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more likely a piston noise. A rod large end diameter will enlarge when hot, opening the rod bearing clearance. The pistons are worn or have shrunk and are noisy when cold. when they warm up and expand the noise goes away. Keep driving it.It will last despite the noise.
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Old 01-08-2011, 08:05 PM
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I would agree will latechs assessment,,,most likely piston slap especially if the noise is completely gone once warmed up.
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Old 01-09-2011, 06:46 PM
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ok tHANKS FOR THE INFO.
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Old 01-09-2011, 06:51 PM
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I just changed out the rod bearings in my corolla after the same scenario. It turns out that all 4 were worn. Threw em in, started it up, and it ran like a champ. It was fairly easy to change them out, not so much to get to them.
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