My Honda knocks when the engine is cold. It always follows the same pattern: About 50 seconds after starting the car it starts to knock. It's so loud that at first I thought I'd thrown a rod but it doesn't act like a thrown rod. As the car warms up the knocking gets quieter until 3 to 5 minutes after the temperature gauge goes to full warm-up the knocking can no longer be heard.

The above happens if the outside temperature is between the mid-30's to the mid 70's. However, if the temperature is lower than the mid-30's then the knocking starts almost immediately rather than waiting 50 seconds to start. If the temperature is higher than the mid 70s it won't knock at all. My OBD II reader shows no codes.

Could something be causing the timing to advance to excess when the engine is cold and cause this noise or is it more likely to be mechanical? Any advice? Thanks in advance.

 

I'd try to pinpoint the location of the sound. "Knocking" makes us thing of spark-knock, or preignition. But there's a lot of other stuff, less serious, that you can check.

Open the hood, set the handbrake, start the engine, then quickly go out & listen. Maybe have a scrap piece of garden hose to use as a "poor-man's stethoscope".

If you can pin the noise down to (for example) a rattling bearing in an idler pulley, that's a lot different than "knocking".

 

Car is overdue for timing belt change, if it's never been changed (7 years or 105K miles). Noise could be loose tensioner or idler.

A rod knock that persisted for that amount of time and only starts after 50 secs of running sounds like something other than rod or main bearing.

A loose crankshaft pulley bushing (rubber sandwiched between outer pulley and inner drive) might cause a noise and gradually disappear.

Exhaust noises can be rattling noises that will sometimes disappear as exhaust warms.

Need an inspection on a rack to locate noise source more precisely.

good luck