Diesel Engine Longevity Revisited

12 Sep

Some years ago I wrote this blog post about the longevity we can expect from marine diesels. I pointed out that the engines on our family ferries often went over 20,000 hours – once to 26,000 – before a rebuild. Those were the old Ford engines, which were replaced with John Deere engines about eight years ago.

We have finally had to swap out the first John Deere for a rebuild…after 46,000 hours, the equivalent of running it 24 hours per day for over five years straight.

Now these engines have a markedly different usage pattern than most marine diesels. That is, they are hammered hard, sometimes for 24 hours a day, making 400-yard trips, with the operator slamming them back and forth between forward and reverse dozens of times per hour, which leads to the first lesson: They like this. Diesel engines like to be hammered. It makes them happy.

The second lesson is that people who talk about rebuilding diesels after 3000-5000 hours are doing something wrong, which in most cases is under-using, and under-abusing the engine.

The only new practice I’ve added to my diesel maintenance repertoire is to send out an occasional oil sample for analysis. Blackstone Labs in Fort Wayne, Indiana did a good job of this, and will even mail you a free test kit and instructions. The analysis tells you a lot about what’s wearing in your engine, about how well your oil is holding up, and about any changes you should make in your engine oil or oil change interval. In my case they said I could change my oil every 120 hours, while I’ve been shooting for every 100, so that saves me money!

This article was syndicated from The Adventures of the Vessel Condesa


  1. Clark Beek

    Hi All, Great comments from many who know much more about this than I do. In our boatyard we do very little engine work, aside from maintaining the yard’s boats, but we see all kinds of horrors. Given that re-powering, even with a modest 2 or 3 cylinder Yanmar, is going to cost $20K or more, sure hate to see all these diesels falling into uselessness from lack of use.

  2. Donald Durand

    Oil analysis is best done for a few oil changes in a row to get a baseline and then see trending. NAPA provides a better deal than Blackstone as NAPA provides TBN along with the oil analysis for about $16. TBN (total base number) is needed if you are running the oil for an extended period of time since it tells you how much of the oil’s additive package is left to counteract the acids produced by combustion. When the TBN is 2 you should be planning your oil change, getting the oil and filters on hand. When it gets down to between 1.5 and 1.25 you should change the oil.

  3. Gerardo Padilla Canizales

    Thank You Mr. Clark

    Excellent article

    I’m at the Power Energy Plant Business since long time ago and had a lot of questions regarding engine life for engines running 24/7 just stopping every 400 hours to do Maintenance
    I really love Diesel engines and we drive at home
    Mercedes Benz Diésel Cars getting wonderful results at mileages and savings
    My only bad experience was with Ford engine 6.4
    In 3 different units engines runs only by a short terms and then get broke easily no matter they had a wonderful Maintenance..

    Kindly Regards

  4. Rux

    Hey ,sonofasailor35,the reasonin marine school they told you to run a (marine engine at full power only 10 0/0 of the time is because marine engine st full throtle are way past its normal power rating. Up to 200 0/0 past normal power.

  5. David Charter

    This is funny most of you people are lost in the past you should update your technology a diesel engine is designed to create lots of unburned fuel and it collects inside the motor there is only one way to stop this from happening and that is by using a hydrogen generator as a additional fuel source. When hydrogen is introduced into the mixture of air n Diesel the hydrogen burns 99.9% of the fuel and keeps the engine clean and the motor will last 1 million times longer without needing an overhaul !!!!!!

  6. sonofasailor35

    I took a four-day diesel mechanics class for sailboat owners at the Annapolis School of Seamanship. They told me you should run your diesel at max rpm 10% of the time. When I tried this, I had alternator belts failing, and unless I caught it right away the engine would overheat and I’d have to change the burned oil.

  7. Andy Smith

    Excellent article, I’ve been a heavy plant mechanic 40yrs. When people say diesels are dirty, oily, loud, and should done away with. I’ve been privileged to work on many types of diesels as you say work them hard and hot but service regularly. What they don’t say is thanks to the engineering wonders for building roads houses all our surroundings and future. Long live the old oiler

  8. Bob

    I have a 17 year old ford 7.3l with 324,000 miles. Replaced glow plugs a year ago, use Diesel Extreme (6oz) each fillup. Still runs well, does have slight miss when first started, stops in a few seconds. Plan on replacing injectors, fuel pump and pressure control soon. Love this motor, I change fuel filter every 5k and oil every 3k. Other than that just run hard.

  9. Stephen Brackley

    Had a Volkswagen car with a 1.7 litre 4 cylinder diesel engine,17 year old.Recently scrapped, because of the emissions scandal and government plans to deminish/ tax diesel.Achieved 211000miles,no failures.Smashin’motor.

  10. Phil

    Timely article. I wonder what should be done to a 30 yrs old OM636 with 800hrs on it? Are.you implying a simple oil test will tell me how much it has left?

  11. Greg

    I have a pair of marine Cummins 6BT series 315 hp in a 36’ flybridge sports cruiser. At what revolutions should they be spinning at for optimal longevity and of course gallons/NM travelled please? Peaking at 2800rpm with current prop pitch and dia

  12. Beryl Isaac

    For what it’s worth. I am a Heavy equipment mechanic on large machines. I rebuilt the 2007 international 466 engine in my service truck 4 years ago. I milled 14 grooves tangentially from the outside of piston top face to combustion bowl. 7 grooves are ⅛” wide .062 deep on outside tapering deeper toward bowl to depth .165″. The other 7 grooves start at outside flush tapering same taper to bowl. Oil stays very clean. Have 1900hrs on current oil and still see through it. I do use a Franz bypass oil filter on it to. The grooves have made the engine much more low torque engine.

  13. RL

    I worked for Cummins for 15 years. In 1980 they were field testing an L-10 engine that was oil cooled. Only water went through the head for the cab heater. It was made to run hot. Never released the engine for production.

  14. Steve

    Im in total agreement with running my Cummins correctly. 40 years commercial driving with zero engine failures. 8.4 million miles is proof they like to run.
    I add Diesel Service to my 04 Cummins at every fill up and only warm it up for 60sec before driving.
    BTW changing fuel filters is a inexpensive way to stay out of the shop.

  15. Allan

    In other words, Diesel engines thrive on heat, and heat comes from burning more fuel, i.e. working that engine! A Cummins instructor once told us that optimum operating temperature of a Diesel was mostly limited by the materials it was made of and they were experimenting with ceramics so they could run hotter, even eliminating the cooling system. Further back, before electronic controls, the rule of thumb was that an idling Diesel had twice the cylinder wear as one pulling a heavy load (unburned fuel was a major culprit).

  16. Ron

    the problem with Diesel’s now are they are trying to pinch the emissions so far down that they are costing too much to run actually because of the failure mostly electronic mostly bad fuel

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