Yamaha Water in Engine ....indicator light back on

[Blackbird]

As you have probably noticed, we've been having some very cool (by our standards) days in Florida lately. When the ambient temp swings, condensation can form in a gas tank if the tank is near empty. Keeping the tank near full with non-ethanol gas may help or solve your issue. Good luck.

 

[seasick]

As you have probably noticed, we've been having some very cool (by our standards) days in Florida lately. When the ambient temp swings, condensation can form in a gas tank if the tank is near empty. Keeping the tank near full with non-ethanol gas may help or solve your issue. Good luck.

I just don't understand that argument. First, I do agree that ethanol fuels can 'absorb' water vapor so the relative humidity of the air in contact makes a difference. My issue is that the amount of surface area exposed to the air in a tank is pretty much the same with the tank mostly full versus mostly empty. My conclusion which may be incorrect is that the rate of absorption is the same in bolt cases all other things equal.
Condensation on the other hand may be different but condensation occurs when moist warm air contacts a colder surface. Depending on which side the moist air is on determines which side has condensation.
I find it difficult to not believe that for the most part an aluminum tank and its contents like gas will both be close to the same temperature and when one cools or warms, so does the other.
The air in the empty tank space may or may not be at the same temperature since the ambient air may be warmer during the day and cooler when the sun goes down (in temperate climates). In not so temperate climates, the air during the day may be quite cold and even colder during the nighttime. The colder air though has less moisture content though.
In order for there to be a lot of condensation, the air temps and tank temps have to be different and the air has to get replaced with new air since as it's moisture condenses out, it gets drier.
Tanks do breath to an extent but mostly due to expansion and contraction of the tank's contents, gas and air.
Tanks with combo fills allow air to get in but are not so good at letting air out as long as the filler cap in on securely. At a minimum, the amount of air exchanged is reduced due to the check valve in the filler. ( open vented tanks will act a bit differently.)
Note that many tanks are also foamed in and that helps insulate the tank and slow any temperature changes due to ambient air surrounding the tank.
As I have noted many many times, I just don't see a lot of condensation related water in the gas issues at my club. I hear a lot of folks who say that they got water from condensation but in 90% of those cases, either rain leaked in the tank ( mostly due to a bad fill cap o-ring) or they got a bad load of gas. It's hard tp prove bad gas but once in a while you get multiple boaters getting stuck at sea from bad gas and later find out that other folks who gassed up that day at the same station had the same problems.

I said I could be completely off base on the topic but it amazes me that I have not seen and controlled laboratory or real world test of the argument about storing a boat with a full or empty tank.
Folks will respond to this and say "I always store with an empty tank and never had a problem". You will also hear comments like " I always store with a full tank and never had a problem"

Personally, I will say " I store with some gas, maybe 1/4 maybe 1/2" and never had a problem"
Maybe my argument is 'All wet"!

 

[wspitler]

I understand your logic, but exposed Internal surface area increases significantly with an empty tank. If I keep my tanks full, I have much less of a problem. However, 350 gallons is a lot to carry around routinely. I still will get about a quart of water out of my tanks in six months. Around here we have morning dew so heavy that it appears it may have rained. This is sImilar to the process on the inner tank walls that are exposed to air as the tank breathes. As the temperature drops during the night, as a percentage, humidity increases significantly. (think sea fog) At some point the humidity becomes high enough that you get condensation on surfaces. If that condensation runs down under the fuel it is trapped and cannot evaporate. At least that’s my theory and I’ve proved to myself with fuel samples and sealing my fuel caps with plastic to prevent rain or washdown entry. In my previous aeronautical life bringing a cold soaked aircraft with empty tanks into a warm hangar could produce gallons of water. The water content of jet fuel from the pump is strictly controlled. Our fuel tanks were drained from the bottom on a daily basis unless they were used continuously. I had E10 gas when I first got the boat, but I ended up getting some phase separation and it actually caused problems with my engine before I got a water alarm. When I am religious with it, my preventive maintenance system for water in my fuel tanks works very well.

 

[DennisG01]

To add to the above, and (maybe) better explain the "store completely full or completely empty" thing (which I have always subscribed to)... condensation forms when there is a difference in air vs material temperature. This primarily refers to the wall of the aluminum tank. If the tank is empty, then the aluminum walls can change temperature as quick as the air temp does since there is no gas in the tank acting as a thermal heat source. If the tank is partly full, the walls do not change temperature as quick and condensation can form. With a full tank, there is no (very little) wall "area" to allow condensation to form.

Florida, for example, will definitely be more prone to these problems than us in more northern states.