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MTBE is nasty in ground water

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MTBE and ethanol are added to gasoline to oxygenate it. the two don't mix well and end up creating a gel that clogs filters and injectors. MTBE is being banned in many states. as the ban occurs ethanol is used in its place and you end up with a mix of the two in your fuel tank. this hits boats worse than automobiles because of the increased possibility for water intrusion.

there is a very good discussion in boatus "seaworthy" magazine, as mentioned in this article (search on ethanol or MTBE to find the relevant info.).

i added this new topic so everyone can hear the sad news. this info is also in a thread about pulpy substance in the fuel system.

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Mad.gif Well, just for the record, our Federal Government MANDATED and REQUIRED the use of MTBE by the oil industry back in the late 1980"s (i may be off on that date). So, the industry then got sued for all the groundwater pollution it caused - from leaking, underground tanks. How I love the Government Mad.gif

Let me correct one thing - MTBE has been banned for some time. Over 5 years, but someone else may have a better date. So, the chances of mixing ethanol laced gasoline with MTBE is remote. Let me also add that engines have to be "rated" to burn ethanol (multi fuel use). This is due to the fact that alcohol is less volatile than gasoline (has less energy too) and the engine compression ratio cannot be very high or you get pre-igniton (knocking) which can damage your engine. Also, the fuel system has to be designed with alcohol in mind - some rubber products get eaten by alcohol. BTW, do you realize it takes MORE energy to make ethanol than to burn it?? Ethanol could not without the tax subsidies the Government provides (read, without your and my tax dollars).

Finally (sorry, I've gotten wound up here), alcohol LOVES water. So, if you store fuel with ethanol and water gets in the system (condensation within the tank, usually) it really gets nasty since they will combine. That's probably what that stuff in the fuel system is.

So, grasshopper,

Lesson #1 - Never put ethanol laced gas in a marine engine

Lesson #2 - Never trust the Government


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"the vent will constantly allow moisture laden air to find its way into the empty tank. Fluctuating temperatures over the winter can exacerbate this, and you can really pick up a lot of water. Also, there's a safety issue. When you empty your tank, you leave small amounts of gas or diesel and also fumes. Fumes can be highly explosive. There's a much lower probability of this with a full tank."

Ok, I'd like to see some REAL research on this, rather than the 'my father did it this way' method. Sounds like the fuel vent infuses moisture the way some people infuse watermelon.

"If you were to store a boat without fuel you'll get days of high humidity and cooler nights. When it hits dew point you'll get water formation. It'll slide down to the bottom of the tank. At end of storage period you'll have significant amount of water in tank."

Again, REAL research might be nice. When it 'hits dewpoint,' do you get condensation on your windows?

Sorry for the somewhat off-topic venting.

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Good point and well taken. Here's some of what you want: condensation occurs when the air space above a liquid has enough water vapor in it to condense. The dew point is the temp that the air needs to reach to there. That is a function of the humidity level and the air tempereature. Here in Houston, we have relative realative humidity levels in the 60 to 80% level all the time. The air vent in a tank does allow the outside atmosphere inside, and all you need is for the air temp inside the tank to drop down to the dew point (usually 60-65 in the summer here), and the water vapor in the air space above the gas well starts condensing. Therefor, IMHO, it's always best to store your boat with a full (to brimming) tank. I make a point of filling my tank at the end of each weekend - I do not want my boat to sit a couple of weeks even without a full tank Biggrin.gif I do use StaBil in the winter time. Seems to work.

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Thanks for the reply. Kind of interesting stuff, actually.

How about this: In the summer my tank has roughly 8-20 gallons of fuel at any given time. That leaves well over half the tank empty. Because of my climate/location we have HEAVY dew on a regular basis all summer. 90% plus humidity most mornings when I awake with so much dew on my cover you'd swear it rained. NEVER have I had a problem with engine running poorly or water in the gas. And in the past three seasons, that's with NO FUEL/WATER SEPARATING FILTER.

Perhaps winter storage differs for me as well, with the cold temperatures here in the north. I can tell you, however, that for nearly 10 years I have stored my boats with the tank almost empty and NEVER had a problem with poor performance and/or water in the gas.

Just my experience, but food for thought. YMMV

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I've always stored with a full tank, but bought into the idea that a plastic tank won't cause condensation the way a metal tank will. For the 1st time ever, I put my boat away this year with an empty tank. I guess I'll find out in the Spring.

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Don't know if this is ok or not. But I always tape shut the tank vent. I have stored inside and out like this. No explosions yet, and no fuel problems. My tank never has more than 10-20 gallons in it. More like 5-6 when skiing.

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Since you are in NY, I would assume you do not have the temperature cycles in combination with the humdity that we have here in Humid City, AKA Houston. It's the air temperature in combination with the vapor in the air space in the tank. It has to cool enough to reach the dew point to precipitate liquid. Could be the outside air temp does not stay down long enough to drop the air temp in your tank down low enough. The laws of physics are fixed - when you reach the dew point, liquid will form - and if there is water in the air above the gas in your tank when that occurs, water will form and then drop to the bottom of the tank. So, if you minimize the air space (or eliminate it by topping off - but don't foget evaporation) you will minimize the possibility of that happening.

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Over winter, and being being stored inside, perhaps the temp flux and humidity are not such to cause problems. During the summer, with the excessive dew, it is interesting that condensation disease hasn't caused a problem. Or, maybe the condensation in the tank thing is an uraban myth.

Or, maybe the laws of physics cease to exist in the vicinity of my Response. Either way, never had a problem.

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