Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 13 of 13
  1. #1

    Default Mercury outboard fuel consumption

    Ahoy,


    Saiboat Challenger 7.4

    http://sailquest.com/market/models/chall24.htm


    powered by a two stroke Mercury outboard motor, Serial No. 7066273

    Question:

    -fuel consumption per hour at half RPM, three quarter RPM and full RPM, expressed in litres.

    Any idea?

  2. #2
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,100

    Default Re: Mercury outboard fuel consumption

    Quote Originally Posted by inspektorgadget007 View Post
    Ahoy,


    Saiboat Challenger 7.4

    http://sailquest.com/market/models/chall24.htm


    powered by a two stroke Mercury outboard motor, Serial No. 7066273

    Question:

    -fuel consumption per hour at half RPM, three quarter RPM and full RPM, expressed in litres.

    Any idea?
    None whatsoever!!!

    Let's start with a horsepower....

    Rule of thumb for 2 stroke consumption is GpH@WOT=hp/10

    Without actually measuring had much is being used nobody can tell you...

    Chris.........
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

  3. #3
    Supreme Mariner Silvertip's Avatar
    Join Date
    Sep 2003
    Location
    Midwest
    Posts
    25,770

    Default Re: Mercury outboard fuel consumption

    Put the pencil away, forget the formula, and put a decimal point one position to the left of the last number in the horsepower rating. 40 HP = 4.0 gallons per hour at wide open throttle.

  4. #4
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,100

    Default Re: Mercury outboard fuel consumption

    Quote Originally Posted by Silvertip View Post
    Put the pencil away, forget the formula, and put a decimal point one position to the left of the last number in the horsepower rating. 40 HP = 4.0 gallons per hour at wide open throttle.
    Isn't that what dividing by 10 means????
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

  5. #5

    Default Re: Mercury outboard fuel consumption

    Chris and Silvertip,


    Thank you for your answers.

    Chris, can you translate WOT?

    I assume when you both talk about gallon it means American gallon(3.78 l.) not Imperial gallon(4.54 l.)

    Is that right?

  6. #6
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,100

    Default Re: Mercury outboard fuel consumption

    WOT, Wide Open Throttle.... For the purpose of this rough rule of thumb, use 4.

    Er, you're new to boats aren't you?

    Chris..........
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

  7. #7

    Default Re: Mercury outboard fuel consumption

    Hi AChris,


    Altough I bought this sailboat in 2005, I don't have much free time to go on the water.
    So, more or less stll I'm kind of new to boating.

    Again, what gallon is? American or Imperial?

    Any rough rule for a diesel engine fuel consumption?

  8. #8
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,100

    Default Re: Mercury outboard fuel consumption

    Use US gallons.... No rule for diesels, sorry.....
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

  9. #9
    Chief Petty Officer
    Join Date
    Jun 2004
    Location
    iowa
    Posts
    474

    Cool Re: Mercury outboard fuel consumption

    so a 115HP will get 11.5GPH? I assume this is for 2-stroke, 4's are different.

    So with a 6gal tank, I can run for 1/2 hour. Mmmm... ther is something wrong with my motor!
    Chris

    Up a river without a DAM lake!

  10. #10
    Supreme Mariner Silvertip's Avatar
    Join Date
    Sep 2003
    Location
    Midwest
    Posts
    25,770

    Default Re: Mercury outboard fuel consumption

    Achris -- in case the decimal point thing slid past you, it was "tongue in cheek". There are people that go faint when they see a formula regardless how simple it is.

  11. #11
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,100

    Default Re: Mercury outboard fuel consumption

    Quote Originally Posted by chrisg View Post
    so a 115HP will get 11.5GPH? I assume this is for 2-stroke, 4's are different.

    So with a 6gal tank, I can run for 1/2 hour. ...
    At WOT (Wide Open Throttle), yes.... Now if you know how far you travel in 30 minutes at WOT, then you have a mile per gallon figure to start working with for speeds other than WOT...

    Chris.............
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

  12. #12
    Captain mthieme's Avatar
    Join Date
    Oct 2007
    Location
    The Dena, MD
    Posts
    3,268

    Default Re: Mercury outboard fuel consumption

    My 35 HP Merc burns about 1 gallon per hour at 3/4 throttle.
    My 25 HP Merc burns 3 gallons in 1 hour 40 minutes WOT.
    But neither is pushing a displacement hull,

    Nothing is so broken that Government can't make it worse.

  13. #13
    Commander
    Join Date
    Jan 2004
    Location
    Poulsbo, WA
    Posts
    2,262

    Talking Re: Mercury outboard fuel consumption

    Actually, the old HP/10 formula was thought up in the days when 2-stroke outboards were rated at the crankshaft.

    So, if you use this on a later-model outboard rated at the prop, the value you come up with is gonna be a bit on the low side.

    But, HP/10 is sure a lot easier to figure out in your head than HP/8.21 or whatever correction factor you jack into the equation!!!

    Here's a good example of this:

    Old Merc 1150 rated at crankshaft, approx 11.5 GPH WOT;

    Old Merc 1400 rated at crankshaft, approx 14 GPH WOT;

    Later-model Merc 115 (which was for all intents and purposes a 140 rated at the prop as 115HP), approx 14 GPH WOT.

    And so on, and so on.

    Still lots easier for my Pea-Brain to divide HP by 10 and then just jack in a bit more GPH to come up with a S.W.A.G.!!!

    And of course the original formula works great on all the Antique Fossil (er I mean "Classic") Mercs we're still playing with!

    BTW it shouldn't matter what type of hull you're pushing, if the motor is truly running at WOT, in its rated operating rpm, it's gonna consume the max amount of fuel.

    Of course, the type of hull you're pushing will greatly change the Speed and MPG values, as will cruising at the most efficient speed for the hull/motor configuration; but we're not talking about those, only specific consumption at WOT.

    Cheers........ed

Similar Threads

  1. Mercury outboard oil consumption question
    By Neptune1 in forum Mercury & Mariner Outboards
    Replies: 16
    Last Post: April 19th, 2010, 05:11 PM
  2. fuel consumption Mercury 402 40HP
    By DutchMerc in forum Mercury & Mariner Outboards
    Replies: 3
    Last Post: June 16th, 2008, 07:08 PM
  3. Mercury 50 fuel consumption & Speedo connection
    By mikewallis in forum Non-Repair Outboard Discussions
    Replies: 2
    Last Post: February 12th, 2006, 05:58 PM
  4. 93 Mercury SportJet 90 Fuel Consumption
    By d.andolsen in forum Mercury & Mariner Outboards
    Replies: 4
    Last Post: July 30th, 2002, 05:40 PM
  5. Need to know about outboard fuel consumption
    By Bill Battle in forum Yamaha & Suzuki Outboards
    Replies: 2
    Last Post: January 26th, 2002, 08:27 PM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic