VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Water in the gas tank

I've had my car just under 3 years now. Among other things I did when I first got it was to clean the gas tank and fuel system, including replacing the fuel line and vaccum tank. A few months ago it started running rough and finally quit. A quick check showed water in the glass bowl fuel filter I had installed.

So I removed the tank, drained, cleaned, and dried it. I thought it odd that after less then 3 years there would be water in the fuel system. When I drained the tank I drained it into a clear 5 gallon container. The first inch or so was pure water.

Since then I have found a large am't of water in the tank two more times.

Ok, where does water come from? Condensation, the gas station where you get the fuel, mean neighbors, and rain. Any place else?

I don't think condensation is the problem. I know I live in a hot, humid environment but that was a lot of water for less than 3 years. Besides, My other vehicles don't have this problem and neither does any one else I know around here. I've been driving 45 years +/- and never had this problem before.

The gas station? I doubt it. The station where I get my fuel is less than 18 months old and it's also where I get the fuel for my truck which is my daily driver. It has not suffered.

Mean neighbors? Possible but highly unlikely.

Rain? The car has been caught sitting outside in the rain but still, somehow I just don't see that as being the problem. It's not like I leave it outside all the time. Rain is what I am beginning to think however.

Your thoughts and suggestions would be greatly appreciated. Thanks in advance.

Your problem is indeed condensation. What happens is the gas in the tank gets warm and expells air/gas mixure. It then cools overnight and draws in humid air which cools dropping out a little water (I know I also live on the humid Gulf Coast). After a bunch of warming/cooling cycles the water will build up. It is much more of a problem with modern gasoline blends then in the past.

The reason that more modern vehicles don't have the problem is the tank is vented through an activated carbon bed removing the water before it gets to the tank.

I have the problem in one of my plastic gas cans that I use for engine testing of rebuilt carburetors. Have had to dry it out twice this past year.

Enough condensation to cause problems 3 times in as many months but not the previous 2 years?

What would one do to prevent it? I try to keep the tank full and never let it go below 1/2 tank w/o filling it, although it may sit at 1/2 for a week or two.

Your gas cap is vented to the outside air. Try an air tight cap for use when the car is not being driven. If its air tight the "humidity" can not enter.

We don't have that problem in this part of Wisconsin. We have high humidity in the summer but the 10% ethanol absorbs the water, the same as adding HEET or a gas line anti-freeze of the iceapropol type (spelling) that lets the water mix with the gas.

I suspect you have two problems. One is condensation. I have found measureable water in my gas can after only a couple of months this past summer and fall. It is kept 1/2 full or more but not sealed. The other is likely water that comes with the fuel.

You just reminded me that years ago a yankee truck driver told me that mixing a gallon of diesel fuel to a tank of gas (about 15 gallons then) would help prevent freezing gas lines. He said the diesel fuel would absorb the water and there wouldn't be enough of it to hurt the engine. Perhaps I should try adding an occassional gallon of diesel fuel to my tank.

You may be right about it being a two fold problem. I hadn't considered that.

If you are not using an ethanol gas mix in LA you can disregard the following and consider yourself lucky.

An ethanol gas mix will absorb water to a point. After about .5% water is absorbed by the ethanol it seperates from the gasoline and sinks to the bottom of the tank.
As this is is exactly where the fuel pump picks up from you have an ethanol mixture that carbureted engines will not handle.
There is a lot of information on the net about this problem and in particular with boats.
For a multitude of reasons this problem is not an issue for your daily driver but will be for a collector car.

I have not yet seen ethanol gas in La. If it's here, it's not advertised.