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
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.
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.
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
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:
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.