Need advise and your thoughts..

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by belliswood, Mar 1, 2018.

  1. belliswood

    belliswood Member SILVER Sponsor

    Nov 21, 2011
    Colonial Beach, VA
    1996 370 SUNDANCER
    7.4 EFI 454
    I own a 1996 370 Sundancer with twin 7.4 EFI/MPI engines with 1100 hours on them. I purchased the boat in 2012 and every year when I do the oil change I have and oil analysis done. The only thing the oil analysis has revealed is trace amounts of antifreeze. The lab says not and issue but to keep an eye on it.

    I am going to do the Great Loop in 2 years and was contemplating having the top ends redone on the engines. I believe that would take care of the trace antifreeze issue and give a boost to the engine performance somewhat.

    So the question: would just doing the top end have any impact for me or should I just leave them be? any suggestions?

    Thank YOu
  2. Espos4

    Espos4 Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    I believe there is a coolant passage in the intake manifold on those engines.

    It may just be a coolant leak from the intake manifold gasket into the crankcase.
  3. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    This suggestion is strictly out of left field, but if I were serious about a Great Loop trip, I would try my best to find a 400, a 410 or even a 450 with 3116 Cat engines. You will burn about 1/2 the GPH compared to 7.4's. This is one of the very few situations where the cost of fuel alone may justify diesels. Then the continued maintenance is a lot less since the Cat engines have a 250 hour oil change interval.

    Just a thought...........
  4. Ididntdoit

    Ididntdoit Well-Known Member

    Dec 5, 2007
    East Coast Florida
    300 Sundancer
    5.0MPI Bravo III
    I would do a leak down test and see the condition of the motors first - unlike a simple compression test, a leakdown will give you better data on ring and valve noted above, the intake and or gaskets could be a likely source of any leak......I would not just do the upper end if it is sealing well, often a new upper end can accelerate wear on an "old" bottom end (ring seal/blowby)
  5. joeyleggz

    joeyleggz Member

    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    I have heard that doing just a top end sometimes on an older motor inadvertently puts pressure on the lower end something to do with the head gasket sizes and increasing the compression q sounds like you have some good running motor’s based on your information from the analysis I would leave well enough alone probably would be a good idea to stay on top of compression checks I think that’s always a great indicator of engine health
  6. belliswood

    belliswood Member SILVER Sponsor

    Nov 21, 2011
    Colonial Beach, VA
    1996 370 SUNDANCER
    7.4 EFI 454
    Thank You all for your response.

    I would like to move up to a 450 but sadly I believe we will be keeping the boat we have. We do love it and it has been good to us.

    A leak down test is a very good Idea. I will schedule with my mechanic once the boa tis in the water. Yes a Leak down would give good indication of the lower end condition.

    So I guess I will leave things alone as far as the antifreeze issue. If it does get worse a gasket top end overhaul would be warranted.

  7. Jus the two of us

    Jus the two of us Member

    Dec 7, 2015
    United States Lake Cumberland
    1998 Sundancer 450
    3116 Cats
    I would not do the top end without doing the bottom end to. Joeyleggz is correct. The valves and rings wear and slowly leak compression. When you rebuild the heads, They no longer leak by, So now the rings are will either have to hold the extra pressure on the compression stroke or leak. Most of the time they will not hold and you will have a lot more blow by from the crankcase. My lesson learned from experience. This is why I bought a deisel boat, And reading Franks posts!!
  8. midexp

    midexp Member

    Oct 5, 2016
    Harrison Township, Michigan Lake St.Clair
    1999 40' Sundancer
    454 merc
    I owned a 1995 37' DA with carbs for 12 years. I had Lowrance fuel flow meters so I knew my exact fuel burn and it was about 0.75 MPG. 40 DA with diesel gets about 1 MPG. But I agree with your suggestion to consider a 40/41. And for that trip diesels. Just your estimate of the fuel delta between gas and diesel is a bit off.

    SCORPIO Active Member SILVER Sponsor

    Apr 7, 2008
    1989 300 DA
    Twin 5.7 Merc Alpha I
    On cars at least, the old wisdom always said, 'never put fresh heads on an Old engine's. As others said, better sealing heads could cause more blow by on an engine with worn rings.
  10. Thornton69

    Thornton69 Member

    Sep 15, 2014
    Northern BC
    1980 24.5' SR custom hardtop
    1984 18' Valco sled
    1984 20' Alicraft- sold
    5.7 260 Merc/ Bravo 2
    Evanrude 115/80 jet
    Kind of odd they would tell you your crankcase is making coolant but not to worry. Just keep taking samples?
    Have you been adding coolant? Might want to try a different lab next go around.
  11. northern

    northern Well-Known Member

    Jan 17, 2007
    West coast Vancouver to Alaska
    380 Aft Cabin 1989 GPS and Charts by Nobeltec
    Twin 454 strait shaft
    If you take the rad caps off, warm the engines up while you watch the antifreeze you can some times see bubbles. If you see bubbles it is an indication you have a head gasket leak.
  12. peterkvs

    peterkvs Member GOLD Sponsor

    Nov 11, 2012
    Guntersville, Alabama
    400 Sundancer 1999
    3116 Cats, 1000 hours
    I'm not sure I like the advice of just watching it. In my experience a trace coolant leak into the oil can quickly evolve into all the coolant in your oil. This makes a mess of epic proportions and it something you don't want to have to deal with on a boat. I'd fix it.


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