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  • #16
    So I don't know how much of this is Urban Legend or not but I've heard from several sources that Costco premium is ethanol free. I always run it in my 70 Mach1 and all my small engines. For that matter it's rare I don't run it in my cars as well as our Costco is 3 miles away and on the way to the freeways.

    https://querysprout.com/is-costco-gas-good/

    I will say this.... I have an 80s John Deere lawn tractor that was going through it's diaphragm fuel pump every year. You'd pull them apart and you could see where the diaphragm had split. The sites I looked at trying to figure out what was on all said it was the ethanol that was causing the issue. I was also having the same types of issues with the carbs on my string trimmer and gas blower. I switched over to using only Costco premium on all these engines and haven't replaced a fuel pump or rebuilt a small engine carb in over 6 years.

    Is it because of the gas? IDK, I really don't but to have that big of a difference the very next year seems odd if it wasn't.

    So, what do I put in the boat? Only Costco premium. It's typically $.20/gallon cheap than the other stations and I get $.04/gallon rebate with my Costco Visa. I plan on sticking with what has worked for me.

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    • #17
      Lowest octane ethanol free which is typically 89 or 91

      Sent from my SM-G960U1 using Tapatalk
      Everyone Dies, but not everyone lives

      2004 Prostar 197, ACME 843

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      • #18
        It's easy to test if it's ethanol free. Get a small jar with a good lid and put a few ounces of the fuel in the jar. Then gently add about a 1/4-inch layer of water on top of the fuel. Close up the jar and using something like a fine point Sharpie, accurately draw a line to mark the height of the fuel/water boundary. Next shake the fuel/water up vigorously, set it back down and give it 10 minutes or so to re-separate. If the water fuel boundary is at the same height as your previous mark, it's ethanol free. If the boundary is above your mark slightly, then it has ethanol. Some of the water will have mixed with the ethanol and stayed in suspension in the fuel and raised the height of the fuel.
        -----------------------------------
        Mastercraft ProStar 2019 5.7L - Current
        Mastercraft X25 2014 6.2L - Current
        Nautique 200 OB 2012 5.7L - Current

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        • #19
          WI guys, what brand's stations are offering ethanol free in the higher grades ? I use a station that is closest to the cabin but could drive further and switch.....

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          • #20
            87 on our LTRs, no issues.

            Some people did a test on Mercedes engines (10.5-11 compression ratio) and found that retarding timing only happened with 87 at high temperatures (95+ F) under high load at high RPMs. The older 5.7s had a ~9.5 compression ratio, so I doubt the higher octane would help them in any way. Finding ethanol-free gas on the other hand...

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            • #21
              I normally just fill up at taco bell.
              -Tim

              Making boomers great again!! Boomin'

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              • #22
                I use ethanol free, 90 octane. I used that in my previous boat. A couple of times I used regular gas and the engine knocked. Never used it again after that. I use ethanol free in my lawn equipment and it all runs much better. It all starts a lot easier after sitting all winter, too.

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                • #23
                  Da cheap chit. It’s just a chevy

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                  • #24
                    I highly suggest that ethanol and octane be two separate discussions. The presents of or absence of ethanol have nothing to do with engine knock. Knock, or preventing pre-ignition, is all about the use of the proper octane, with or without ethanol. You need to first use the required octane or higher, then make the decision of seeking out E-free in the suggested octane or higher.

                    If you can get E-free in the correct or higher octane, thats great, run it! But I would not run E-free in a lower then required octane. The chances of engine damage are greater with the low octane then from the ethanol.

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                    • #25
                      Originally posted by peytonvp View Post
                      That has always been my thoughts behind using the right octane. I know that modern fuel injection systems can retard timing so it is not as much of an issue but I know it is always better to be safe than sorry. The funny thing is my friend has 4 2007 Seadoo RXT, which are the supercharged skis, and he has run regular 87 octane since day one and he has over 300 hours on each ski. Skis call for premium but I would say he has had pretty good luck. That said I am not as brave and always run premium in my turbo skis.
                      Well, that's the thing- if an injected engine knocks, the ECM pulls back the timing to whatever extent is needed and that limits performance.

                      There's a whole lot of small engines that are injected, too- lawn mowers, snowblowers (we can explain those to you guys who never see snow, if you want), tractors, etc. I see that as a good thing, though- I have had to explain the easy way to start small engines to some of my neighbors who just about wore their arms out trying to get the things going. My next door neighbor broker wrist and her mower and snowblower both have electric start and even those didn't start reliably after sitting and when I showed her how to build compression and get some gas into the cylinder, they started on the first pull. The place that services them never told her about that.

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                      • #26
                        fuel with ethanol can cause issues with seals, metals and rubber lines if you own an older (pre 90s) engine switching to a non ethanol fuel will help from the issues mentioned above. For instance I didn’t run all the ethanol fuel out of my carb on the 81 and when I went to check things to start after winter the carb was infested with a white-ish covering over any part that still had fuel
                        1981 MasterCraft
                        19' Skier 351W PowerSlot
                        Long gone is the Trans AM waiting for another

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                        • #27
                          Costco premium... upto 10% ethanol, my engine calls for 89.. no 87 and 91 at costco.. hard to come by non ethanol gas by me and the cost differential at the nearest marinas and getting there a PIA and not worth it imo. The engines in our tugs produce most torque at low rpms so why not use what the engine manufacturer recommends.. talking oil is much more fun [emoji16][emoji12]

                          Sent from my SM-G955U using Tapatalk
                          sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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                          • #28
                            Octane is sort of my specialty by profession. I did a write-up on the F150 forum to try to help educate on what octane is/isn't as there is a lot of confusion and misinformation out there.

                            https://www.f150forum.com/f2/end-all...thread-510819/

                            I've heard marine engines have higher octane recommendations than needed because the manufacturers assume less turnover in the gas tank. Storage can degrade octane. The Indmar 5.7L has pretty much the same compression ratio as the Ford 5.4L (9.x:1) which uses 87, so it makes sense to me. If you are refilling the tank every couple of weeks during the summer you can probably get away with using a lower octane. But I would be very careful about using lower octane rating than recommended. Modern engines can retard timing if knock occurs, but it's a fail safe that you don't want to rely on. Plus it costs HP to retard timing. In any case, the final fill-up before winterization should absolutely use the recommended octane rating. There's never a need to use higher octane than recommended.

                            At altitude, a naturally aspirated engine can use lower octane and be just fine. I'm at 4500' and use 87 instead of the recommended 89. Turbocharged engines compensate for lower atmospheric pressure and should use the recommended octane regardless of altitude.

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                            • #29
                              Storage can degrade octane.
                              Are you referring to the actual octane molecule or the (R+M)/2 pump octane rating?

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                              • #30
                                Octane rating.

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