klhutch
Sububan Chicago
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Joined: 09/14/2005
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Roadfrog wrote:Quote:I do know a bit about humidity, due point Etc
It's DEW point, but I'm no expert. However, this guy seems to know his stuff:
condensation myth
Yes it is dew point, not due, point but they are pronounced the same so it is a natural error to make. Your web reference does not "know his stuff". Not completely anyway. Tanks may not be freely vented to the air anymore but they do draw air in as you empty them. You have a partial vacuum in the tank, not a complete vacuum. So if you were to start with a full tank on a humid day, drive until nearly empty, and then store for the winter you would start with a tank full of humid air. If the dew point of the air in the tank is 60F and the ambient temperature drops to 35F then the water vapor in the tank is going to condense out of the air inside the tank until the dew point of the remaining air is 35F. That is what the dew point is, the temperature at which the air can no longer hold the amount of water vapor mixed with it.
How much water? Your reference does not understand what makes water vapor condense so it is questionable whether he can calculate the amount of water available correctly but I will assume that he has and that you can get about 0.8 oz of water from a 200 gallon tank. So with a typical 50 gallon tank you might get 0.2 oz. If your gasoline contains ethanol that will probably not be a problem. If is does not then the 0.2 oz water will settle to the low point of the tank, which is right where the fuel pickup is.
Still 0.2 oz of water is not much so your engine will suck it right up and spit it right out and you might have to crank a tiny bit longer to get your engine started. No big deal. Now let the temperature drop to 25F before you try to start it. That 0.2 oz of frozen water might just be plenty to block your fuel pickup. Now you are not going anywhere until you thaw out that water!
Fuel condensation is not a myth. The prevalence of gasohol has probably made it a non issue for most folks most of the time. Keeping a full tank in the winter for a vehicle you drive daily probably never was an issue because winter air is dryer and you have a really hard time getting enough water vapor in there in the winter to cause trouble. Likewise most of us will not go into winter with a tank still full of August air that started at 90F and 95% humidity and that limits the amount of moisture in the tank.
Ken
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