Is it normal to lose rpm's when motor warms

[tblack111]

I have a 25 hp 4 stroke Mercury EFI. Is it common for this motor to lose rpms later in a fishing day when the air warms? Losing 500 or so as the day grows long.

 

[trendsetter240]

Re: Is it normal to lose rpm's when motor warms

Usually not 500rpm. Are you maybe taking on some water? Or filling up your boat with fish?

Try feeling the tell tale stream and see how hot it's running later in the day. It should be quite warm but not hot.

 

[Texasmark]

Re: Is it normal to lose rpm's when motor warms

Combustion torque increases with dense air and if you dig around on here you will see numerous articles which deal with the subject of things like that including winter performance vs a summer mid afternoon in comparison. So it is not uncommon to have rpm's move around 500 rpm. I know for a fact that my boat is 2 mph faster in February than it is in July. Course part of that could be the difference in pump gas formulation for winter vs summer driving.

HTH,

Mark