Is it OK to run at 3400 rpm for 1 hour

HPLou

Petty Officer 2nd Class
Joined
Sep 15, 2007
Messages
196
Good Day
I have twin 1989 Merc 4.3LX and was wondering if it was OK to navigate at 3400 RPM, 27-28 MPH (On plane) for 1 hour ?
Should I slow down for a while to cool off the engines ?
Thanks
 

ttankmoran

Seaman Apprentice
Joined
Mar 22, 2015
Messages
39
For most engine setups that is probably the most economical cruising range and the easiest overall on the engines. You could run sun up to sun down every day at that RPM/speed and not have to worry about the engines.

If you run into heat problems doing this you have something else wrong.
 

Mark72233

Ensign
Joined
Jul 11, 2014
Messages
926
HpLou, I agree 100% with ttankmoran, engines are made to run if everything is good then they should run all day in those ranges. with no need for cool downs. What engines don't like much is idling for long periods and the quick up and downs.
 

JoLin

Vice Admiral
Joined
Aug 18, 2007
Messages
5,146
3400 is where I usually run mine. Just like your car engine, they're designed to run at normal operating temp and moderate rpm's nearly forever. On plane at 3400 rpm is my sweet spot. With the hull out of the water the engines are just loafing along, driving the boat at 23-24 mph
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
If you like that RPM range, I say great. It is not asking the engine(s) to work very hard and the mileage will be better there then WOT. So go for it and have fun... :thumb:
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,464
Ayuh,.... At 3400 rpms, those motors would gladly run the next 3000 hours, non-stop, so long as ya fed 'em gas, 'n changed their oil,......
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
I run my 5.7l at around 4k for extended periods when I need to get someplace. Normally I cruise at around 3200-3500.
 

cptrick3

Petty Officer 2nd Class
Joined
Apr 11, 2015
Messages
157
Once you have more time on the boat you'll find a sweet spot somewhere between 3 and 4K. You'll get the best economy, and the boat will feel happy. Don't forget to play with your trim. Trim up until your rpm increase but not so much that you feel your loosing control.
 
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