Diesel Transfer Tank Question

I just purchased a 36 gallon diesel transfer tank. I mounted it on my trailer yesterday and this morning when I went out to install the pump I peered into the opening where the pump goes and saw what appeared to be some moisture on the bottom of the tank. It was very difficult to see how much, but was enough to where when I inserted a stick and rubbed the bottom of the tank, the end of the stick came out moist.

We did have a heavy rain overnight, but I see no way that water could have entered the tank. While I did remove the plastic cap on the opening yesterday, I did screw the pump on although not tightly. It appears that what I'm seeing in the tank could be condensation, but I suppose it's remotely possible that some rain water could have entered.

Is this something I need to be concerned about, or is it normal for some moisture condensation to occur in a tank like this? I've read that it's not uncommon for diesel fuel to have some small amount of water in it. I'm sure I can return the tank and exchange for another one, but hate to do it since I've already installed it on my trailer.

Appreciate any thoughts on this matter. Thanks.

Yes condensation ,hot humid days cool nights . Keeping full of fuel helps . Keep pickup tube off bottom a little bit.

It's likely condensation on the tank. We run good quality water separator and fuel filters on our transfer tanks to avoid problems.

If you want be fussy about it you could run a shop vac blowing in the pump out fitting and out the filler neck it might take a few hours depending on how much water is in it.
As said above keep a full tank when you can and put a good filter /water separator on the pump.
Its wet most of the time here in BC so ill take mine out once a year and stand it up on an angle so i can use a drill pump suck out any crap thats accumulated . Between that and the filter i never have any trouble.

Anytime I use a tank for the first time I like to put a few gallons of fuel into it and slosh it around and drain just to get anything out of it. After that just a good filter.

For small amounts of water you can get fuel filters that also contain a desiccant. Your transfer tank needs a filter anyway.

Yep - need a filter. Every fuel tank needs a filter. Our 500 gal tank on the yard has a filter on it. Fill up our slip tanks and it's filtered again before going into the machines. Can't filter diesel enough on these new high pressure fuel systems. Gotta keep your fuel as clean as your DEF.

Yes, water can enter your tank through the bung threads the pump is in. Consider a water pipe without thread sealant. The bung threads are much shorter. My tank got water in it through the bung.

Tanks get moisture in them every time the atmospheric pressure drops, and every time you pump fuel out. If you sealed the tank to prevent moisture entry, you wouldn't be able to pump the fuel out.

Your questions been answered but we try to keep our tanks topped off as often as possible to help keep the condensation to a minimum.

terex herder said:

Tanks get moisture in them every time the atmospheric pressure drops, and every time you pump fuel out. If you sealed the tank to prevent moisture entry, you wouldn't be able to pump the fuel out.

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The cap for the fill opening is usually vented.

I put a small drip leg on any fuel tank I can, even on the machines. A valve on the drip leg makes it easy to burp out any condensation or water. I normally use a Tee fitting with a 2 to 3 inch leg out the bottom and the fuel line coming out the side of the T. Harder to do with a field tank unless it mounted permanent somewhere.