Cruising RPM, Hrs, GPH, and longevity Tug and Cut diesels

[BB marine]

Late on this trread ~ regarding engine loading and life

I was told this by several Volvo car and Mac truck reps regarding the Volvo turbo/supercharged engine. I was curious about the reliability compared to the red/silver blocks. Remember these are 2 liter engines putting out ridiculous horsepower. There is a lot of case pressure. Told the the engines are fine for suburban use but are having issues in mountainous states - blowing seals from lugging them up mountains

Marine engines area always climbing a hill. This is the reason they should be propped correctly. The engine needs to be loaded asper manufactures recommendation. The engine should turn 4150 rpm to be loaded properly at any rpm. Anything below 4000 rpm WOT the engine is climbing a mountain!!! If you run at 2000 rpm all day long but your WOT rpm is 3800 rpm You are climbing the mountain in over drive lugging the engine. The D3 is a good little motor. It is not a heavy duty truck engine. Propped correctly and used at 30 to 40% load propped correctly you will be boating for years!

 

[Diatom]

2011 C26 Yanmar 4BY2 180, 1100 hours.
Modified original 12" tabs with BB-inspired drop fins, major improvement. Automated with Mente.
Cheap adjacent haul-out means bottom frequently cleaned.
WOT a touch over 4000 RPM, never go there.
Fast cruise 3600 RPM, crossing the Georgia Strait, holds 17 knots except where fighting currents (Active Pass, Fraser River).
Slow/typical Gulf Islands cruise 3350 RPM.
Temperature creeping up slowly over past year approaching 199F, something needs a flush.
Yes boat "gets heavier every year".
/tmm

 

[Miss Stress]

I would have to disagree with the Volvo tech. The right answer if you want to maintain longevity of the engine is NO MORE than 90% of WOT for extended periods of time with a variation of rpm between 85% and 20% rpm. Recommending to run a 3.7L 4 cylinder 300 hp diesel at 90% RPM of max RPM is a marketing statement. Yes you can do it but the longevity will be decreased. A D4 300 hp should turn a minimum rpm of 3500 rpm. Preferably 3650 rpm. It is rated at 3500rpm. Meaning the max continuous rpm to operate the engine at would be 3150 rpm ( If your max RPM is 3500 rpm on that given day) Meaning when you change the loaded weight of the boat, more passengers, full fuel, full water, a little slime on the bottom you need to run the engine up to max rpm and confirm what Max rpm is. Then adjust your max 90%. rpm. You will be surprised how much it changes if you have a prop that is marginally over propping the engine. Most Rangers and Cutwaters are marginally over propped. Most folks don't operate their engines at this max load. I'm not a max rpm fan for gaging what is the max rpm I can operate the engine at. I use fuel burn as my gage. Fuel burn equates closely to engine load. A good high cruise speed would be operating the engine at between 70% and 80% load. Most Volvo Penta EVCs will show engine load. It is close but I feel fuel burn is more accurate. The amount of fuel burned is the energy used. A Volvo Penta D4 300 hp burns about 15 GPH WOT. A good max cruise speed fuel burn would be around 10 to 11 gph. The engine would be loaded to about 70% load. Using this fuel burn number as a max cruise speed will be consistent no matter how you are loaded. What will change is speed and rpm. The load will be the same. You may find that if you are loaded down with extra passengers or gear. Your fuel burn is 11 gph but your speed and rpm has dropped.

Many folks have stated I run at 3150 all the time. I ask even when you are loaded heavy? The answer often is "it doesn't matter that is 90 % of my max rpm". I question again ,"even when you are loaded heavy?" The answer normally is why ?. My answer is if the load changes the engine is loaded more and often it will not tun 3500 rpm @WOT . It may only turn 3375 rpm . So you would be running the engine closer to 95% of max rpm. If you use fuel burn as your gauge the engine load will be consistent 70% to 75% load burning 10 to 11 gph and the engine longevity will be maintained. I don't sell Volvo Penta products, or represent them. This is my opinion of how to operate an engine. Your boat high cruise speed may be a little slower but your engine may last a little longer for you or the next owners.

Brian, I certainly agree with you on engine loading.
I've retired from owning my own trucking business, but still own several Diesels, including our C-28.
Most over-the-road truck engines AVERAGE 40 to 55% percent load during their lifetimes.
I'm also a piston engine pilot; aircraft engines usually operate at 65 to 75% cruise power, within certain specified limits.
I like to say it like this:
An engine has "X" number of horsepower-hours. If you use more horsepower, you'll have fewer hours of life. less horsepower = more hours. this is NOT a linear formula. Running any engine at close to or at maximum power (not strictly RPM) will significantly reduce hours of life.
Diesel engines especially need to "work" from time to time to generate internal combustion heat and "burn-off" deposits and contaminates from low-speed, low load operations.
Proper Maintenance gives more hours.