Pausing to cool down

[shellone]

When on a 100 mls. + tour with a 24footer and a Mercruiser 5.0 MPI, is it sound advice to slow down off gliding speed and forward idling for some minutes or is it better to keep it running at a steady rpm? My cruising speed is 25 knots @2800 rpm, and I welcome knowledge whether it is advisable to change that regime now and again, say e. g. throttle it up a notch to 3100 rpm?

 

[drewm3i]

Better to cruise...much better water flow.

 

[Scott Danforth]

service your cooling system if you have overheating issues.

a properly maintained cooling system can run until you need to stop for fuel without ever coming off plane.

I would say you could run flat out, however not on a stock recreational motor.

 

[shellone]

Thank you very much and humble greetings from a sailor who has no mechanic experience. We in fact just cruised 4 hours 10 minutes @24.3 knots average without ever touching the throttle, not even the trim. Water temp gauge seemed glued on 55 degrees Celsius even when, upon arrival, I let it idle for 15 minutes.

 

[shellone]

service your cooling system if you have overheating issues.

a properly maintained cooling system can run until you need to stop for fuel without ever coming off plane.

I would say you could run flat out, however not on a stock recreational motor.

Thanks again, for the advice. Could you please guve me some pointers as to what needs to be done to a stock engine ? Is a double circuit cooling system with open water intake part of it ? What else is essential? I sure do not feel my life well protected by those plastic impellers and without a serious termomether (there I would like to have two, for each cyl. bank).

 

[Scott Danforth]

if you want to run flat out on a stock recreational motor for long periods of time. take the motor out, take it to your local machine shop. swap out the cast pistons for hypereutectic pistons. do a complete balance job on the motor, use coated bearings, upgrade the leaf style timing chain to a roller. then the motor will survive many hours at full throttle.

as for cooling. install a water pressure gauge for an outboard (with a tube you run back to the water jacket - not one with an electric gauge and sender). if your water pressure drops, you have a water flow issue. BTW, water pressure will indicate a problem a full 2 minutes before a temperature gauge or any buzzer will. assuming you watch the gauges. IMO much more important than a temperature gauge that already doesn't read accurately.

 

[Scott06]

Thank you very much and humble greetings from a sailor who has no mechanic experience. We in fact just cruised 4 hours 10 minutes @24.3 knots average without ever touching the throttle, not even the trim. Water temp gauge seemed glued on 55 degrees Celsius even when, upon arrival, I let it idle for 15 minutes.

no problem at all here with these numbers . 55c is just under 140 F so completely fine . You do not need to vary the rpm. only needed when you are breaking in a new engine