I took the boat with a 2003 two-stroke Mercury 60 hp out the other morning when the temperature was around 20 degrees. This was the first time I had used it when the temps were this low. As soon as I started the engine it sounded totally different than it normally does. It didn't sound like it was hurting it and it ran fine, but even after the engine had warmed up it still sounded different. It wasn't missing or knocking or anything like that, just the sound at idle was totally different.
Any thoughts guys maybe some have you have noticed something similar to this. Thanks in advance.

The air that cold has a tendency to change the way we hear things but with cold air the fuel mixture is different. You will notice a power increase in most motors because it is getting more oxygen. Just take your time letting motor temp come up before taking off.

ever notice how our holeshot is better in cold weather vs. hot weather??
not to mention being cooler the engine makes more power, but cold water is denser therefore the boat sits higher in the water. when a boat sits a bit higher, the exhaust is higher, making the engine a bit louder.

similar to salt water conditions!

Thanks for the help. Puts my mind at ease. I never knew why they holeshot better when it was cold. Thanks.

Yep, colder air has a higher "expansion" rate. It produces more combustion since it is colder. It is just like running an intercooler on a Turbine engine. The cooler the air going into the engine, the more combustion, thus more power.