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  1. #1

    Default Mercruiser 357 4v alpha

    Hi all, So being a old school car guy, I understand the impact that alcohol has on fuel systems, but I also know that if I run it consistently in my old jeep it is fine. The only real issue seems to be if I let it sit long enough to dry out. Shouldn't this basically be the same in a carbureted V8 in a boat? Am I missing something? If I run regular premium gas all summer and then switch to ethanol free gas for the last tank before winter wouldn't that be about the same?

    Is anyone here doing this? how has it worked for you?

    I'm just struggling with the $1 plus premium for ethanol free gas and would love to be able to just run regular gas. If this is really a disaster waiting to happen then talk me through it a bit.

    Thanks for the input, and sorry for the list of questions.

  2. #2
    Join Date
    Jun 2008
    Island Heights, NJ,

    Default Re: Mercruiser 357 4v alpha

    NO.... fuel tanks on boats are vented overboard by law. With temperature and humidity variations, the alcohol in the gas absorbs water from the atmosphere. Eventually the ability of the ethanol to hold water is overwhelmed and free water happens in the tank... At this point the effective octane of the fuel is degraded and in humid environments, alge can grow at the water fuel interface in the gas tank. Eventually the water seperators in the fuel filters fill and bad things happens (engine no go) rather abruptly... furthermore, in a carbed engine, the residual ethanol laced fuel in the carb also absorbs water... I've noticed a chemical reaction in the carb, usually in the fine jets, where the ethanol laced fuel develops a rock hard sandy colored deposit that ignores carb cleaners and air hoses, and is only removable mechanically. Studious use of fuel additives somewhat mitigates this problem. Regular use of the boat and keeping a full tank helps. As you mentioned, "consistently in my jeep" is fine. Boats rarely get used consistently.
    Last edited by sandkicker; 08-27-2018 at 06:32 PM.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

  3. #3
    Join Date
    Sep 2003
    New Tripoli, PA, USA!

    Default Re: Mercruiser 357 4v alpha

    I've been dosing the fuel with Startron additive over several years now and have not had a problem.


  4. #4
    Join Date
    Dec 2006
    Chaumont Bay, N.y., USA

    Default Re: Mercruiser 357 4v alpha

    Ayuh,..... I'm with Bob,.... ethanol is the devil's curse, I burn nothin' but ethanol free fuel,.....

    At today's prices, boatin's still cheap compared to the gas spike of 8, 10 years ago,.....
    Any Grease is Better,... Than No grease at All....

  5. #5

    Default Re: Mercruiser 357 4v alpha

    Quote Originally Posted by sandkicker View Post
    NO.... fuel tanks on boats are vented overboard by law. With temperature and humidity variations, the alcohol in the gas absorbs water from the atmosphere. ... Regular use of the boat and keeping a full tank helps. As you mentioned, "consistently in my jeep" is fine. Boats rarely get used consistently.
    Thanks for taking the time to reply. I know this is a somewhat contentious issue.

    Ok, so the exposure to humidity is definitely higher, but vehicle fuel tanks are also vented... so while I sort of see this I can also see a counter argument. Here in Florida humidity is high pretty much everywhere, almost year round. Definitely a factor though.

    As for the used regularly I definitely see your point there, although if I know I'm going to burn through a tank of gas in a weekend, then it doesn't seem like a problem. I guess it's really about personal risk tolerance, and ensuring you don't allow your gas to get stale. What does that mean exactly, i'm not sure. 1 week, 1 month, 3 months?

    As for the deposits in the carb is definitely new info for me. I haven't ever noticed this personally. Most of the carbs I've had to rebuild were from letting them sit til the gas dried up and left a gummy residue, certainly not any fun to resolve. I'm not sure what to make of this, but it seems like it should affect all vehicles not just boats in particular. It certainly needs more research on my part.

    For me I am leaning towards the idea that if gas with ethanol works in a land vehicle that is used regularly, then the same should be true for a boat. While I don't deny that ethanol free is better gas, It holds that if E10 is an engine destroyer I shouldn't use it in my other vehicles either. I have been using E10 in all of my land vehicles, because that's whats available most of the time and It hasn't done any harm to my jeep, or any of the other newer cars, lawn mowers, weed eaters etc. Granted I don't run the boat every day, but I do run it every weekend.

    So given all of that I'm trying to determine if there is some factor that makes E10 usage in a boat unique from using it in a land vehicle. So far all I have is increased humidity exposure, and Stale gas which allows the octane to change, and allows for the separation of water. Of course I can't account for increased humidity, but I can control the stale gas condition.

    I don't have a fiberglass fuel tank so that isn't an issue, and I have a newer mercruiser motor which indicates from the manufacturer that it can be used with E10 and 87 octane.

    Are there any other factors I'm missing? Thanks again for engaging in the conversation.

  6. #6
    Join Date
    May 2010
    DC Burbs/Maryland Eastern Shore

    Default Re: Mercruiser 357 4v alpha

    I can't agree that fuel sitting in a tank will go bad as long as the tank is kept full. Too many studies have confirmed this, and the addition of "stabilizers" is generally negligible in keeping fuel from "going bad". Of course it has a shelf life...the volatile agents evaporate leaving a lot of stale fuel but that takes years. However this has been and will continue to be argued about as long as there is ethanol in fuel. You make your own choice there.
    The real damage from ethanol fuel comes from the rubber fuel hoses. The inside of the hose breaks down and causes all kind of difficulty. The solution is simply to replace the old fuel hose with new alcohol resistant hose.
    Practicing the ancient art of ren-ching

  7. #7

    Default Re: Mercruiser 357 4v alpha

    I'm with you, in the end everyone has to make their own choice, but unfortunately this topic is so filled with anecdotal evidence it's really hard to make an educated decision, mostly I am trying to gather all of the potential factors so that I can make a decision based on my circumstance.

    In my case I have a recent re-power, as of two years ago so I'm fairly certain that my fuel lines are all new from then. Possibly down in the fuel tank there might be some old line sections, I'm not really sure, as I haven't had the sender out. Anyway good point. Thanks for pointing it out.

  8. #8
    Join Date
    Apr 2016
    barnegat NJ

    Default Re: Mercruiser 357 4v alpha

    Automobiles have a closed fuel system,it's pressurized, Moisture can't get in. Boats do not have this luxury

  9. #9

    Default Re: Mercruiser 357 4v alpha

    I know this is true to some extent for newer vehicles, but air from the environment still needs to be let into the system in order to prevent a vacuum on the tank, usually through a charcoal filter. I don't know how much that reduces the humidity, if at all before the air that is drawn in, but on older vehicles the cap is usually vented. It is an interesting point though, definitely a difference between a boat fuel system and a car fuel system.

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