115 4stroke yamaha speeds
- Thread starter smirkin
- Start date
I have owned diesel engines which I have run for thousands of hours at the same RPM, with no harm in boats. In trucks, cars and RV's the RPS will change as you go down the road. On the other hand, my RV (Cummins 8.3L C series) often runs for several hours on the highway at a constant 1500 RPM. There is also a myth that you cannot run diesels at idle for long periods of times. Look at On the road truckers--they leave the engine at a fast idle for many hours while sleeping to run the AC unit. Some newer rigs will have a generator, to decrease pollution and save fuel for the AC and heat.
Same for outboards; I often run the engines at 3500, 3800 or 4200 and keep then there for hours. No harm.
During break in period --yes, you want to vary the RPM. But once broken in, I see no harm in running for hours at the same RPM.
Same for outboards; I often run the engines at 3500, 3800 or 4200 and keep then there for hours. No harm.
During break in period --yes, you want to vary the RPM. But once broken in, I see no harm in running for hours at the same RPM.
Robert H. Wilkinson
New member
The warranty for my Volvo Penta required changing rpms and not running at wot for the first 20 hours. After that - no problems running at a steady rpm.
As for diesels - the Yanmar that powers my off grid system runs at 1800rpm every day - for over 9000 hours now. A diesel that is run at a constant rpm with a constant load will outlast 1 that is run at different rpms with a varying load. For example a Yanmar on a irrigation pump can go 50,000 hours but the same engine on a welder might go 10,000. The only thing I know that a diesel doesn't really like is running with no load. Not that it harms it - it just runs smoother with a load. They love to work
The only other concern might be that some engines tend to carbon up if run too long at low rpms. I had this happen with a Honda generator once. I was running it at a low idle, just using the 12 volt charging circuit. Using only this circuit would not engage the auto idle to increase rpms. I thought it had blown a connecting rod because it would only turn over a half rev. Honda told me to pull the head and check for carbon. After cleaning the combustion chamber and piston tops it ran fine!!
Running at different rpms isn't going to hurt your engine tho - the biggest engine killers are lugging and drastic load changes (as in the case of a welder).
Regards, Rob
As for diesels - the Yanmar that powers my off grid system runs at 1800rpm every day - for over 9000 hours now. A diesel that is run at a constant rpm with a constant load will outlast 1 that is run at different rpms with a varying load. For example a Yanmar on a irrigation pump can go 50,000 hours but the same engine on a welder might go 10,000. The only thing I know that a diesel doesn't really like is running with no load. Not that it harms it - it just runs smoother with a load. They love to work
The only other concern might be that some engines tend to carbon up if run too long at low rpms. I had this happen with a Honda generator once. I was running it at a low idle, just using the 12 volt charging circuit. Using only this circuit would not engage the auto idle to increase rpms. I thought it had blown a connecting rod because it would only turn over a half rev. Honda told me to pull the head and check for carbon. After cleaning the combustion chamber and piston tops it ran fine!!
Running at different rpms isn't going to hurt your engine tho - the biggest engine killers are lugging and drastic load changes (as in the case of a welder).
Regards, Rob
Robs excellent post reminds me that I have a friend who got 25,000 hours out of a Yanmar 3 cyl running a 9 KW genset. Same engine in thousands of sailboats rated at 30 hp,, in this case derated and run at a constant 1800 RPM.
Many of the new 4 stroke outboards in commercial use (which often means hours of idling) last thousands of hours. Most die from abuse not over use.
Many of the new 4 stroke outboards in commercial use (which often means hours of idling) last thousands of hours. Most die from abuse not over use.