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  1. #1

    buying gas on the water with pre-mix

    I'm running pre-mix on my 1999 Kawai stx 1100. I would like to occasionally buy gas at a marina, so I'll be, mixing and pumping while floating.

    Would it be safe for me to first fill up with gas (then I know how much gas it took) then with my handy dandy oil/gas mix calculator app on my phone tell me how much oil to put in.

    Normally when I fill up while on the trailer at a gas station, oil goes first, then gas. in know increments of 5 gallons, then 3, then 1 or so. I do this because I like to "mix" the oil by putting gas on top, then "shake, rattle, and roll" on the way to the boat ramp.

    Not sure if I can really have that luxury to do this at a marina.
    thoughts?
    waxman
    Last edited by K447; 08-06-2014 at 01:01 PM.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Even putting the oil in first at a roadside has station there is risk the oil will not fully mix with the gasoline during the drive to the launch ramp. I have seen the result of the added oil dropping to the bottom of the gas tank and not fully mixing. Too much oil to the carbs, then too little.

    Pre-mixing oil into gasoline is a hassle and even when you are doing it 'properly' it is way more fooling around than filling with straight gasoline and having a working oil injection system.

    My understanding (I do not use pre-mix myself) is that the 'proper' method goes as follows. The required oil quantity (for the entire fill up) is to be put into a small gasoline container of maybe one or two gallons size. Partially fill the container with fresh gasoline, then cap the container. Shake the container to thoroughly stir the oil into the gasoline. This is supposed to pre-dilute the oil into enough gasoline that it will then easily mix into the rest of the straight gasoline.

    Poor the heavy oil + gas mixture from the container into the PWC fuel tank, then fill up with the required amount of gasoline to match the amount of oil. Hopefully the added gasoline blends readily with the pre-mixed gasoline and you end up with the desired oil to fuel ratio spread evenly throughout the fuel tank.

    Of course this whole process is highly inconvenient!

    I am not aware of a method of adding oil in the correct proportion to the gasoline as you fill the watercraft tank.

    So the oil gets added before, or after. Before is difficult since you do not yet know how much fuel the partially empty watercraft tank will accept. After means adding straight oil if there is not enough room to pour in another gallon of fuel with the oil pre diluted.

    And you must carry the small gas can in the watercraft somewhere if you want to refuel elsewhere.

    I suspect many people just end up guessing the oil amounts and hoping the oil gets mixed well enough that the engine does not get starved for oil. Which is ironic as the reason often given for switching to pre-mixed oil is that it is 'safer' for the engine.

  3. #3
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    Pre mix sucks just for reasons like this. Its easier to maintain an oil injection system and not have any hassles.

  4. #4
    Tommy Pantsdown's Avatar
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    I've never had a problem on my GPR's. I've done it for years. Lots of people will say negative things about it but won't point to an actual failure from it that they've had first hand.

    For years I've carried Gatorade bottles marked with the ratio per gallon on the sides. I'd add a few gallons, add oil. Add a few gallons, add oil. Add a few gallons, then add oil. You just need to be mindful and do small amounts. 3-4 gallons at a time. Then 1 gallon at a time when you're close to full.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Tommy Pantsdown View Post
    ... won't point to an actual failure from it that they've had first hand.

    For years I've carried Gatorade bottles marked with the ratio per gallon on the sides. I'd add a few gallons, add oil. Add a few gallons, add oil. Add a few gallons, then add oil. You just need to be mindful and do small amounts. 3-4 gallons at a time. Then 1 gallon at a time when you're close to full.
    Actual failure ...

    If the oil is properly mixed with the gasoline each and every time then you might expect that pre-mixing the oil could never lead to an oil related failure.

    The first risk is that at some time the oil will not be properly mixed with the fuel. Wrong amount of oil added, or no oil added. People can get distracted while fueling, someone else might be refueling the machine without knowing the correct method, etc.

    But even if the oil is correctly mixed into the gasoline, it is still possible to hurt the engine. In effect pre-mix is a double or nothing bet. The fuel system and the carburetors must be 100% good or the engine will not be properly oiled.

    If a carburetor gets plugged up and runs lean then the oil delivery also runs lean. So not only is that cylinder running hotter than normal, it is getting less oil than normal. Oil injection would not do this.

    If a carburetor gets completely clogged and the cylinder is not even firing, the rider may need to continue running the engine to get back to the dock. The engine is going to be running badly with a dead cylinder, but that dead cylinder is still running the piston up and down. Since there is no fuel flow, there is also no pre-mix oil going to that cylinder. There is plenty of air flow through the dead cylinder since the engine throttle is open. The dead cylinder will have minimal oil available and the piston rings will start to run dry.
    Last edited by K447; 08-06-2014 at 10:00 AM.

  6. #6
    Tommy,
    Thanks that is what I thought.

    K447,
    I believe your answer about mixing is "text book correct". That being said I have been mixing at the pump as mentioned for 3 seasons (and I live in a region with loooooong seasons) and have not had an issues.

    Me and the pre-mix boys do what we, do cuz its what we do; and as you mentioned you are not one of us. so my question was not really directed towards someone with you experience.

    I appreciate both of your gentlemen's feed back.

    Waxsworth

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