Boating mag April 2020 says ethanol-mix will wreck boat engines.

Some comments on issues discussed above.

Regarding fuel separation. There are practical reasons to worry about this. While each batch of gasoline departing the fuel depot should be stable for long periods on it's own, it turns out that if you mix two stable gasolines that get there differently, the resultant mix is not necessarily stable. And it needn't be you who's doing the mixing. An independent service station which procures from multiple vendors can end up with a separable mixture in their supply tank. Mixing different grades of fuel that get there with exactly the same stabilizers can also become unstable. For instance, mixing E05 and E10, both from the same brand and containing the same stabilizers, may not result in a stable mixture. And that can happen easily enough when you fill your vehicle. So for vehicles that may not get used for a while, sticking to one fuel source can significantly reduce the risk of problems. Long term, separated moisture can leach out all kinds of salts and other solubles from the fuel and additives.

The issue with water in ethanol gas is counter-intuitive, to say the least. There are a huge number of studies published on the subject over the last 30 years. Adding water can reduce the corrosive tendencies of ethanol gas a lot. In some cases, by orders of magnitude. To whoever mentioned they were washing the alcohol out of their small engine gas, any benefit was probably from the water left behind in the gas, not from removing the ethanol. If they had effectively flushed the alcohol out, the resulting gas would have an octane rating in the 60s and the motor would run like crap, if at all. But this is all very sensitive to the exact fuel chemistry and water chemistry, with impurities needing to be quantified to ppb accuracy. There are several corrosion studies that consider seawater ingress and condensing coastal air in ethanol gas fuels.

There seems to be a divide on the perceived effectiveness of fuel quality enforcement. My American view is that there isn't any. We just let the big oil refiners and motor companies sort it out themselves. There is no way to compare gas historically because the understanding of what can be sold as, say, 87 octane E10 changes from week to week. There is no testing, no enforcement, and no real liability associated with selling bad gas. Fraudulent and adulterated fuels are very common. When consumers switch away from sketchy gas stations, the owners have to find better supplies.

 

Done this many times washing ethanol out of gasoline, and it runs great in all my lawnmowers. Not an octane drop to 60, more like a drop of 5 points is what I have read. Same thing would run fine in my boat and generator which has a cr of 8 to 1. I might do it for a lawnmower or small carbed engine because it saves the carb from corroding. But not on the boat as it simply would be too much of a pain and it wastes 10% of my gas money.

After I modified my 1970 fuel boat system to be pressurized like a car, but set to 1 PSI using the New EPA Perko emissions caps, the gas stays much fresher in the boat. You also need the fuel demand valve at the tank, I use the Attwood version. I have 30 gallons in a tank, and that fuel is maybe 2 years old, the boat sits in a marina slip and the boat engine runs fine, the fuel is clear.

Example PERKO Inc. https://www.perko.com/help_guides-epa_compliant_replacement_pressure_relief_gas_caps/

Using the vented fills these fuel caps are fantastic, they click just like your car. A car sets the PSI to 2 for venting, and these are set to 1 PSI. So what happens is much of the time when boat is sitting that big lake of fuel in the tank never gets exposed to the humid air. The double acting valve stays shut unless the pressure difference exceeds 1 psi above or below where it was when you last opened the cap. The fuel demand valve refuses to pass fuel unless a suction occurs from the fuel pump, so a pressurized tank can not leak any fuel say if a hose came off. I think the Attwood valve can be overcome at 18 psi in the tank, something that will never happen.

The 1 PSI for the boat was set lower than the 2PSI for a car mainly for a safety factor due to the boat tank may be really big and maybe not as strong as the small fuel car tank. BUT AFAIK, the tanks have to be able to hold 3 PSI anyway some kind of USCG regulation. So they could have gone with 2 but for safety went with 1 psi for venting. I have found typically not enough temperature changes happen daily to ever pressurize the 150 gallon tank, but after a winter, I did open my fuel cap today, and the system had pressure in it. When gas warmed up from the winter it built up a small amount of pressure in the tank, I had priorly opened it when it was 40 degrees and today it was 80 degrees, so that is a good test to know it is working.