What Causes the Abnormal Noise During Cold Start of Odyssey?

[NatalieDella]

The reasons for the "ticking" sound during cold start: Faulty hydraulic lifters: This may be caused by improper oil usage, low oil pressure, or wear in the hydraulic lifters themselves, allowing air to enter and resulting in the ticking noise. Worn valve rocker arms: This leads to excessive valve clearance, preventing timely formation of an oil film during cold starts. Carbon canister purge valve operation: The sound from the carbon canister purge valve is normal. The reasons for the "clunking" sound during cold start: Clunking sound within half a minute: If it disappears afterward, this is usually caused by the expansion of the catalytic converter when heated, which is normal. Cold start: A loud clunking sound during cold start is mostly due to issues with the engine timing system, such as wear, elongation, or loosening of the timing belt/chain, or failure of the chain tensioner. Only occurs when AC is on: If the noise appears only when the AC is on, it may be caused by friction in the AC belt.