Moving from gas to diesel - maintenance costs

Discussion in 'General Maintenance/Repair Questions' started by mmcguire2002, Apr 12, 2018.

  1. mmcguire2002

    mmcguire2002 Member PLATINUM Sponsor

    547
    Mar 3, 2008
    MDR, CA
    2003.5 Sea Ray 340 DA
    8.1 Horizons
    Hello - considering moving up from my 340 SDA to a 420 SB. Trying to get a realistic view of the difference in cost to maintain diesels versus my current gas set up with the mercruiser 8.1’s. Thanks!
     
  2. SKybolt

    SKybolt Member

    294
    Nov 11, 2014
    Long Island, NY
    1988 460 EC Sea Ray. w/12.5K Westerbeke Genset.
    Twin 6v92TA Low profile's (475hp) with Alison Gears.
    That is a very subjective question. It's mainly based on engine type. But based on your current year boat, I'll guess it has Cummings with ZF transmissions. If that is the case then the general maintenance is basically the same. Change the fuel filters and oil every season or 100hrs. Transmission oil every other year or so. and Clean/replace all of the air filters every season.

    Sounds familiar right? Well, not so much. The fuel filters are a little more complicated, but changing the oil might be a little easier. The fuel filters need to be drained and flushed out then new cartridge and re-filled. The oil change is easier because now your using the on board oil changer and basically use 5 gallons per engine. So you need to start with an empty 5 gallon bucket (preferably with a top) and it's out with the old and in with the new, pretty easy. Cleaning the airseps is a little more messy but not bad. just takes some time. The only other thing is maintaining the coolant, that should be changed out every 3-5 years, checked every season, but based on usage and the raw water pump impeller every other year, again based on usage.

    The real difference is constantly looking after the engines and catching what is about to go wrong, mainly hose clamps breaking and getting loose. water/coolant/fuel leaks. Diesel engine vibrate a lot more then gas engines. There compression is 3 times more then gas so things can loosen up and leak. Catching that can be the difference between a good day and a real bad one. Running a diesel engine boat vs a gas engine boat is night and day, and well worth the extra effort needed. You will love the stability of the cruise a diesel provides.
     
  3. importmonkey

    importmonkey Opinionated Member

    889
    Jul 9, 2015
    Middle River, MD
    2007 44 Sundancer
    QSC 500s
    PM me your email and I'll send you my maintenance spreadsheet. It'll give you a good idea of what you'll be in for.
     
    mmcguire2002 likes this.
  4. b_arrington

    b_arrington Active Member

    583
    Feb 21, 2007
    Setauket, NY
    270 Amberjack (2006)
    AB Ventus 9 VL RIB
    350 Mag MPI Horizon w/ BIII
    1998 Envinrude 15 HP 2-stroke
    FWIW, I was considering a boat with a Cummins QSB 6.7 diesel engine. I had always assumed that diesel engines required a good amount less maintenance and were overall less costly to run compared to gas engines.

    I asked the owner of my boat yard what the real differential is and if my assumption was right. He said that in the past that may have been true for mechanical engines. But with modern diesel engines that are all electronically controlled, have intercoolers and turbos, the maintenance costs are about a wash vs. gas.

    I can't say if that's really correct or not since I still have a gas engine.
     
  5. ttmott

    ttmott Well-Known Member

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    An investment into diesel drive train is significant so the preventative maintenance steps are also be a bit more significant. Oil needs analysis every 100 hours and before oil changes, Fuel requires a regimented treatment, and engine coolant should be analyzed at least every 5 years. These are routine for diesel engines to ensure the service life and costly repairs are avoided; these normally do not apply to a gasoline fueled engine. I think I probably spend $500 per year on the analysis and fuel treatment; insignificant but essential. It's difficult to really level load costs between the two power plants as the diesel engine is really designed for different service factors. About as close as one could get is the Merc. 8.1 vs Cat 3126 or QSB but even then it's not a one for one trade. I will say, however, that in the overall lifecycle of the hardware, the diesel would prove to be more cost effective. This is to assume a lifecycle of 5000 hours which not only includes maintenance per the manufacturer's requirements but fuel, fluids, initial purchase costs, resale value, at least one replacement for the gasoline engine vs a baseline capability of 5000 hours for the diesel. So, this isn't a one year what's it going to cost me evaluation. Lastly, but probably most importantly, it's about what the boat is to be used for; are you going across the river to a restaurant, 20 miles across the lagoon to camp out, or a 130 miles to the Bahamas?
     
  6. mmcguire2002

    mmcguire2002 Member PLATINUM Sponsor

    547
    Mar 3, 2008
    MDR, CA
    2003.5 Sea Ray 340 DA
    8.1 Horizons
    Thank you for that. I do understand the long term benefits of diesel versus gas and I do use the boat for ocean passages, so the performance and reliability is on the plus side as well as not sleeping on a ticking time bomb (gas) at night, which I do frequently. I’m jus trying to ascertain the routine annual maintenance costs of diesels, so I can see what I’m in for, as well as any major service intervals and their costs. I can take good and bad #’s, I’d just like to be as informed as possible before moving forward.
     
  7. bbwhitejr

    bbwhitejr Well-Known Member

    Apr 14, 2013
    Lake Lanier GA
    2007 44DB
    Cummins QSC 8.3s
    We are in our 8th month of diesel ownership. Had all fluid analyses done during the surveys along with two Cummins Techs on board for the entire day of hull and engine surveys. Everything came back “nothing needed at this time.” We are on a freshwater lake so we are in the “going across the river to a restaurant” group. We moved up from a 260DA. I do all of my maintenance and am learning the diesels. I am almost through with my annual maintenance. Oil changes in both engines and gen-$250 in oil and OEM filters, racors and primary fuel filters-$100, transmissions-$30, impellers-$300, airsep cleaning/recoiling kit-$35. Aftercoolers and heat exchangers had just been done before I bought the boat. I still have the coolant to check out and thermostats. She runs cool so I am not in a hurry. I have also treated every ounce of fuel that was in her when purchased as well as when we have added per Frank Webster’s instructions. Racors have stayed perfectly clean and were and are running on 10micron filters.

    I think impellers will last quite a while the way we use the boat and as clean as this lake is. Plan to replace airseps next year. Will also pull fluid analyses next spring for comparisons.

    As ttmot indicated, depends on how you use your boat. We might put 50-75 hrs/year on here so maintenance cost likely will not compare to someone on the coast, but I wanted the diesels and got a good deal on her. BTW...we have the Cummins QSC 500s. Best of luck!

    Bennett
     
    dtfeld likes this.
  8. mmcguire2002

    mmcguire2002 Member PLATINUM Sponsor

    547
    Mar 3, 2008
    MDR, CA
    2003.5 Sea Ray 340 DA
    8.1 Horizons
    Thanks so much. How often do the after coolers and heat exchangers need to be done and what are we looking at in terms of cost there?
     
  9. bbwhitejr

    bbwhitejr Well-Known Member

    Apr 14, 2013
    Lake Lanier GA
    2007 44DB
    Cummins QSC 8.3s
    I have seen those intervals shown as different from salt to shallow/dirty fresh to clear/clean fresh. I think, and will be corrected here, that in salt you are looking at 3-5 years. Forgot the belts-annually depending on wear-$70-80 for 2.

    Bennett
     
  10. mmcguire2002

    mmcguire2002 Member PLATINUM Sponsor

    547
    Mar 3, 2008
    MDR, CA
    2003.5 Sea Ray 340 DA
    8.1 Horizons
    What is the typical cost associated with maintenance on the heat exchangers and intercoolers?
     
  11. BlueYonder

    BlueYonder Member

    126
    Jan 12, 2015
    Chesapeake Bay
    37
    QSC 8.3 600
    Your engine manual will specify the maintenance interval for your cooling system. it will probably be a combination of X years or X hours whichever comes first. Don't put off doing the maintenance waiting for the engine hours to reach the required number. Freshwater flushing or freshwater operation can significantly increase the service interval. Do the first service at the appropriate time and see how things look if you are operating in freshwater or freshwater flushing the motors.

    I paid $4200 for a complete cooling system service for a single Cummins QSC 8.3.
     
  12. my3sons

    my3sons Well-Known Member SILVER Sponsor

    Feb 24, 2009
    Upstate NY (lake Erie)
    2004 400DB, Onan 9 kw Gen, Highfield RIB,
    Cummins 6CTA
    I have the 6CTA. Heat exchangers and aftercooler O-rings and gaskets are $130 +/- for both engines. I did them when I bought the boat because they had never been done. (freshwater)
    Then I did them again when I hauled this past fall because It had been 4 years and we just finished looping and I had put 1100 hrs on them since the first time. They looked like I had just serviced them, but I flushed the raw water system while we were in salt when I knew the boat was going to sit for more than a few days.
     
  13. mmcguire2002

    mmcguire2002 Member PLATINUM Sponsor

    547
    Mar 3, 2008
    MDR, CA
    2003.5 Sea Ray 340 DA
    8.1 Horizons
    Was that $4,200 per engine, or for both engines? Appreciate the input.
     

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