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Oil Leaks 12V71n

Discussion in 'Engines' started by Kafue, Sep 2, 2012.

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  1. Kafue, Sep 2, 2012
    #1
    Kafue

    Kafue Senior Member

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    How much is “normal” for Detroits Diesel engines to leak oil? I have 12V71n’s.
    This is my first experience with DD’s and I am not used to seeing much oil leakage in an engine.
    The Port engine has the leaks. Stbd very little.
    Each time I have had experienced DD owners and mechanics look at my engines, they say the amount is normal. In fact when I was on a coastal cruise and pulled into a fishing village, one trawler skipper who visited the boat was stunned at the clean engine room and the small amount of oil leaks. Soon I had half a dozen trawler owners who have DD’s visit the boat to see these clean 12V71n’s.
    Both engines were overhauled by a well-respected company in Florida. They were not the original engines, I have the photos of them in the factory. Boat is 1971, engines 1980’s. Overhauled in 2009.
    The pre-purchase engine survey was very good and showed that pistons were new DD supplied with good hatching marks etc. They had approximately 95 hours when I purchased and although they blew smoke a bit at initial throttle, they settled down well.
    Now, after 18 months and 1100 nautical miles, 275 hours of use, the oil consumption has dropped and as for the exhaust, they are running very clean and sound GREAT.
    Oil consumption: dipstick down approx. 1/8th after 9 hrs. run, 2 hour at cruise and say 7hrs. at troll speed of 8/10 kn. Same for both motors.
    Similar consumption if I have a 2 hour cruise with 20 minutes full throttle. I should be able to give litre/gallon use, but I have been keeping them topped up after each cruise so am not certain, will take note from here on. I have to top up the oil after most trips.
    Full throttle, 2250 r.p.m.: 18 to 20.5 kn and running very clean.
    Cruise at 1500 r.p.m.: 12/15 knots
    Thanks.
    Kafue

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  2. Kafue, Sep 2, 2012
    #2
    Kafue

    Kafue Senior Member

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    More images.

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  3. RT46, Sep 2, 2012
    #3
    RT46

    RT46 Senior Member

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    Ummmm, your only issue is that they dont leak enough......
  4. Capt J, Sep 2, 2012
    #4
    Capt J

    Capt J Senior Member

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    You could probably stop some of the leaks by tightening bolts etc...... Sometimes gaskets contract a little after a few years from new. I don't think the leaks are too much for a DD.

    Also, oil consumption. One thing to note with the 12v71's, is that if there is any difference in trim (how the boat sits in the water at the dock at the end of your trip), the dipstick will read totally different.......A lot of times on a SF, the stern will float higher as you burn fuel......an inch or two on the waterline at the stern can make a noticable difference on the dipstick.......next time, before you fuel, check the oil levels.......fuel the boat then check them again......Also some Detroits will puke out the oil if it's right on the full mark and will settle down and stop consuming when it's 3/4 between Add and full........
  5. Kafue, Sep 2, 2012
    #5
    Kafue

    Kafue Senior Member

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    Thanks Capt J
    So maybe I have been over cautious in keeping the oil at full, better to keep it at 3/4 and monitor it to see if the oil leaks lessen.
  6. Bamboo, Sep 2, 2012
    #6
    Bamboo

    Bamboo Senior Member

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    Those leaks are not excessive and not an issue as I see it. Be very careful if you tighten bolts. I also would not add oil unless you are at/below or near the low mark unless you are headed on a long voyage. Some engines may want to settle somewhere inbetween the F and L marks. You may be topping off prematurely.
  7. Kafue, Sep 2, 2012
    #7
    Kafue

    Kafue Senior Member

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    LOL
    That is the problem with asking advice on these engines, I get the answer so often that they are built to leak or if they aren't leaking oil, then there is none! etc.
    I am really getting to like them, mainly because I can do a little work on them without destroying the motor, unlike the MAN's I had which were all computerised and needed an analyst!

    You know you are getting to like them when 20 knots excites you;)
  8. Kafue, Sep 2, 2012
    #8
    Kafue

    Kafue Senior Member

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    Like to hear that. I always have plenty of oil onboard so from here on, I will keep them at 3/4.
    They are using less oil and running better as they get more use. This season should be good, touch wood!
    Cheers.
  9. Bamboo, Sep 2, 2012
    #9
    Bamboo

    Bamboo Senior Member

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    I fill to full and then leave it until they get at/near or below the L mark. I think they use the top half of the oil faster than the lower half.
  10. RT46, Sep 2, 2012
    #10
    RT46

    RT46 Senior Member

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    some of the bolts are open inside to the airbox.

    Ive had a few leaking soot from around the bolts.

    I have had good luck removing the bolts, cleaning the threads, and reinstalling with some permatex. It seems to stop the leaks from the bolts that are open to the airbox.
  11. chesapeake46, Sep 3, 2012
    #11
    chesapeake46

    chesapeake46 Senior Member

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    2 strokes

    I agree with you on liking the 2 strokes.
    A friend and mentor of mine loves them so much that I swear he must have DETROIT tatooed somewhere special on him. He's got 40 W in his blood.

    He told me that, being a detroit, the blower charges the entire engine block with air which is looking for a way out...... any loose gasket or fitting will do.
    Yours look pretty tight and clean, congratulations.

    Mine are 671's & I have one that leaks a little more than the other.
    I have found that keeping them on the full mark wastes more oil and they do burn less when about 1/3 down from FULL.

    Leakers but reliable. Inefficent but reliable.
    I like that I can work on them myself with basic mechanic's tools although I hate to hear the rumors that the replacement parts are not as good a quality as in the past.

    Here is a 671 video that, if you listen hard, you can hear some 2 strokes singing.
    671 Detroits in a sportfish on an afternoon cruise 08 2012 - YouTube
  12. Capt Ralph, Sep 3, 2012
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    The back of the oil cooler will start to leak more where it meets the block. You can not get to those bolts from the outside. Keep an eye on it, in a few years (many, many hours) it will turn into a nice leak.
    It took our stb main 6 years before it got bad and I had to dive into it.

    Your pictures show some slobber leaking from an exhaust port, Next time running, try to snug all those nuts a little more. You don't want that to turn into a real exhaust leak.

    Dipstick tubes, valve covers , ect etc are all trial and test.

    Always let your Detroit sit for a while before you do a serious oil level check. Your engine may try to tell you where the best level is if you watch it.

    My story on that; I helped work on an old boat with 12/71s. Owner kept it's oil full, used a lot and leaked allot.
    One week I ran the boat and waited for the dip stick to read on the bottom scale before adding any oil back. Every afternoon and morning they were checked, they never got low.
    I also noticed the oil sorb towels were not that bad.
    End result discovered; engines were tail down, to much oil around back of crank. oil getting splashed into last cylinder liners and to rear crank (old) oil seal.
    We keep the oil in mid scale @ cold now. No more messy engine pans, consumption way down.

    71s Rule..
  13. Kafue, Sep 3, 2012
    #13
    Kafue

    Kafue Senior Member

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    Many thanks to you all for the feedback.
    Oil level will be 1/2 to 3/4 from here on in and let's see how it goes.
    Your advice makes sense.

    rcrapps, yeah.....71's rule!
    Now seeing as I am superstitious, I will touch wood, and anything else to keep things running smoooooth.
    Cheers,
    Kafue
  14. Capt J, Sep 3, 2012
    #14
    Capt J

    Capt J Senior Member

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    Just don't start knocking on the fiberglass!!!!!!! :D