Cummins Marine Diesel Repower Specialists › Forums › Cummins Marine Engines › Low RPM Cruise
Don Gardner.
I have a 1999 Maxum 4100 SCR with twin 6BTA 330’s. Until the fuel prices skyrocketed I always cruised at 2400 not 2600 RPM’s. Now I am cruising at 1500 to 1600 RPM’s. Do I need to run it up to 2400 to 2600 every 8 hours to keep the engines from having issues?
Thanks for the input Rob. My boat has a planning hull and last winter I added two more trim tabs at the keel line. I can now run bow down at any speed rather than having to stand to see over the bow. Much more efficient and I no longer have to get over the hump. That said, after reading Tonys article on low speed running and your and Steves input I plan to take it to hit cruise RPMs at the end of each hull speed run.
I run 160’s in 330’s as well. If I plan to run hull speed initially I will pump up the rpms to hump speed or planing speed (depending on conditions) or so when I can to get the temps up to 160 and the oil temps up too and then back down to hull speed for my extended time. (This is because for my twin screw efficient flat aft section hull design hull speed is next to nothing as to load) And then when I’m done at extended hull speed run and before heading back into the harbor I try to do a stretch at full cruise for a few minutes.
Thanks for the info Steve. I am running 160 thermostats. My temps are the same as when running at high cruise RPM as are my oil pressures. I run at low RPMs when leaving the dock or anchorage until the temps are above 150, then slowly push it up to the cruise speed I want to run. I will read Tonys tips.
I googled Blaine, WA and I see that you are in cold water. Do you know which thermostat you have? 160F or 180F? Engine temp, oil pressure and other things will help you understand how “warm” your system is. I use the oil pressure, coolant temp and EGT as additional data points for operation.
When we shove off from the dock we run a 2 stage warm up procedure. Our Marina is in a protected bay that has a lengthy no wake zone that we run at 750rpm. EGT is 300F at this point. Once we are clear of the inlet we throttle up to hull speed which is 1140 and EGT increases to 500F. We run at 1140 until I see the oil pressure come down below the “50” mark on the analog gauges. That takes about 10-15mins. At that point I figure we are good to throttle up to 2240 if we are going to run on plane. Otherwise we continue to run at hull speed until we reach our destination, which is typically a GPS waypoint by one of the Lake Erie islands for swimming. On our way back to the inlet we will execute the warm up procedure after pulling up anchor and then run on plane until we are at our approach for entering the inlet. That usually takes 20mins. Our engine temps increase from 158 to 165, exhaust temps increase from 500F to 725/750F and oil temps increase accordingly. When we throttle back the oil pressure is about half way between the 25 and 50 marks on the analog gauges. We then cool down in our no wake zone, with blowers running, and then we dock.
I try to operate in a mechanically prudent manner as I want our boat to last. we have some multi year distance cruising plans on the Great Lakes. So I have adopted some operational procedures to help keep things happy.
I am always open to and looking for tweaks to these procedures so feel free to comment.
There is an article in the Tony’s Tips section titled “Low Speed Running and Break in…..” Give it a read. The last sentence of the third paragraph answers your question. In summary, run low and slow all you want but at the end of your day run up to cruise power for a few minutes to get everything up to operating temp to clean things up should it need it.
I routinely do this with our 6CTA’s. We run 1140 which is hull speed for us. Toward the end of our day we will run 2240.
You must be logged in to reply to this topic.