Another diesel question

[higgs]

We are told that diesels are good for 10 - 20, 000 hours. Yanmar tells me my 3QM is good for 40,000. 100 hours a year is a lot of hours for most of us. A 10,000 hour engine, then, should be good for 100 years. Why are so many people rebuilding and replacing - or is the 10,000 hour figure bogus? If manufactures are telling us the truth, our diesels should outlast us.According to Yanmar, my 3QM should be able to give me 10 hours a day for the next 35 years.

 

[Ross]

Poor care!

Somebody told them that the best operating speed is wide open throttle and they believe it. If any one checks on the service ratings for marine diesels they can find the exact same engine rated for pleasure service, military and law enforcement, and work boat service. For pleasure service they rate the engine for 250 hp at 3300 rpm for 300 hours per year. For law enforcement and military service 200 hp at 2600 rpm 1500 hrs per year, for work boat service 160hp at 2200 rpm 6000 hrs per year. This is for exactly the same engine, the propeller is chosen to create the load at the speed specified and the throttle adjusted to limit the speed.

 

[Honeyman]

They are built...

to run at approx. 70-80% max. rpm for all those hours. Deviation from that like long idle at low rpm, never running at wide open throttle, letting fuel "gunk up", running salt water through them, never changing fuel/oil filter elements, never running up to "operating temperature" and keeping them there, letting them sit for months at a time, are just a few of the main reasons they don't last as long as they should. What's your next question, Higgs?

 

[Nice N Easy]

And your point is

Ross,I fail to grasp your point here. Surely you are not comparing a 3QM, which produces in the area of 20HP, with some big honkin marine diesel which puts out over 150HP.Every word I have ever read, or been told about for these little diesels, states that they survive best, if run at approx. 80% of full throttle. Honeyman is 100% right in the reasons he gave for the little engines not living as long as they maybe should. I would like to know which engine it is that they rate at different horsepowers, for any reason.Since they show more hours at the lower RPM, they might rate the engine so many horsepower at a certain RPM. But an engine that puts out 100 HP at 3400 RPM is a 100HP engine, no matter how much HP it puts out at lower RPM. It may be stated that you can expect so many more hours when run at 1500 than when run at 3000 but it is still a 100HP engine.

 

[Ross]

On any engine the horse power rating is based on

intended service. Little diesels and big diesels wiil last far longer when run at less then full throttle and rated hp. My Volvo diesel is rated at 10 hp at 3300 rpm pleasure service, which means less than 300 hrs per year. But at 2200 rpm it produces only about 4hp. If it were rated for work boat service it would be a 4 hp engine. I believe that I could adjust the throttle setting and push it to 4000 rpm for racing service. I would not expect it to endure that sort of treatment for very long.  My fuel consumption rate at 3300 rpm is 2.76 liters per hour but at 2200 rpm my fuel consumption rate is 1.1 liters per hour. The engine gets to full operating temperature, does not smoke, and pushes the boat at 4.1 knots. at 3300 the engine gets to full operating temperature and pushes the boat at 5.4 knots. Running at 2200-2500 rpm is a far cry from "long periods of idling" and poor fuel quality will have the same effect on all diesel engines.edit to add link:http://www.frontierpower.com/library/makingsense.htm

 

[Liam]

Use

Ever notice that lots of boats for sale that have been cruising will list thousands of hours on the diesel and say "runs great" while some daysailors are having major problems with engines that have 500 hours?That is because diesels are made to be run and run hard for long periods or at least until they are good and hot.I know skippers who start their diesel, go put put for 5 minutes until they are in the fairway, raise sail and shut off the engine. I know others who start the engine and let it idle for half an hour in the slip then shut it down. Both of those things kill an engine.The best thing that you can do for your engine is run it at 80+% of rated rpm for hours and hours on end. They are really truely made to do that. The second best thing you can do is change the oil every 50 hours.With care, it is true that a small diesel will clock 20k+ hours.Engine life is not based upon the total millions of revolutions that it will turn before it wears out as others have stated. An engine that is rated max output at 3500rpm will last longer if it is consistantly run at 3000rpm than if it is run at 1500rpm.

 

[Honeyman]

Geez Ross...

you sound WAY under powered! My 3gm30F pushes my 35.5 at over 6 kts. at 2400-2600 rpm with a clean bottom. I've NEVER run it over 3200 for any period of time other than to "blow it out", but it will make well over 6.5-7 kts at that rpm. You are certainly NOT running at long periods of too low rpm with your setup, just way under powered. Me thinks your's is working a bit too hard, but with the care I'm sure you give it, it will probably last a LONG time which is what "higgs" original post was about.

 

[Ross]

Honeyman, I can sail faster than I can

motor but I often sail slower than four knots and enjoy it. I have a 3:1 reduction gear and at four knots absorb 4 hp at about 2200 rpm on a 13 inch 3 blade 14 inch pitch propeller shaft speed is just over 700 rpm. Calculations show that I would need nearly 18 hp to get hull speed.If I were in a hurry I wouldn't have a sail boat. ;D

 

[BarryL]

hours vs years

Hello,Years of being in a salt water environment take their toll on an engine regardless of how many hours are on it. Rust, corrosion, etc. will destroy an engine faster than worn out cylinders, valves, etc. So the engine may last 40,000 hours if used 2000 hours a year (20 years). But it will probably not last 40 years at 1000 a year.Barry

 

[Big Windy]

Advice

I got some good advice from a mechanic a while back. He said once a month pretend your sailboat is a power boat...take it out and let it run for an hour or so at 80% wot. It's good for it.

 

[higgs]

Bert, I have been told different

i have been told to open her all the way up once in a while as there is a governor. I just can't bring myself to do that having been around gas engines for so long.

 

[Moody Buccaneer]

Time and temperature

The key with any infernal confusion engine is to get the darn thing up to temperature and keep it there for long periods.An oil temperature gauge will tell the tail. The oil needs to get in the 200 degree F range to vaporise any moisture and blown-by contaminates out of the oil.If an engine's cooling system is designed to keep the temperature stable at 80% and not overheat when loaded to 100%, it is capable of over-cooling the engine at lower loads. At 30-40% load the oil takes forever to get hot enough, and the engine is soiling it's own life's blood. At part load, the engine might take 30-45 minutes to get the oil up to temperature, then the oil has to be kept hot for 45-60 minutes to self clean. If you can load the engine up and bring it to temp is 15-20 minutes it will live a longer, happier life.A heat exchanger in the oil system is a good idea. The coolant helps warm the oil then it provides oil cooling if the oil gets hotter than the coolant. Overall temperature is much more stable once past the warm-up stage that shortens the life of most any engine.If you can run the engine at 100% RPM and WOT now and then that's a good thing. If however WOT produces black or white smoke in the exhaust, only run the engine hard enough to keep it below the smoking exhaust settings. Black smoke is too much fuel, white smoke is too little fuel. One just carbons up the engine, the other is a potential engine killer.

 

[Rick9619]

But what about the other things

Perhaps a look from another angle. My 3gm30f with fixed two blader will push my 336 at 8 knots wide open. Ok so that is good for the engine but... from a vibration point, how about the packing gland, cutlass, pressure on the rudder. That is where I get some concern. I try to run mine once a trip, meaning we are at the boat for three or four days. I blow her out, so to speak, for about 5 minutes or until she is blowing carbon free exhaust. Vibration free is normally about 22- 26 hundred and that is 5 knots or so. The proportional loss of life span on the iron genny versus hauling and replacing packing gland and cutlass is... heck I dont know. I havent had to do either yet. Just wondering. What about when you are on the hook and charging batteries? What is a good rpm for these kind of loads on the engine?CheersRick

 

[Ross]

moody you make a good point for engines

not too large. Hull speed for my boat requires 19 HP to install a 30 HP engine would mean that it never has to produce more than 66 per cent of its rated power.