Yes and no. If the diesel fuel was totally dry, like immediately after refining, not likely going to happen in any sort of volume that would show up in a filter. If the fuel was "dry" then there would be very minimal potential for condensation. "Wet" or saturated diesel fuel, fuel absorbs moisture, can cause condensation inside a tank that is partially full but this condensation only came from the wet fuel so you are really not adding much if any to it it is just coming out of the fuel and then back into it..Carl Thunberg wrote: So the real question is, is a tank that is 3/4 full susceptible to condensation? I hate to say this, but I think the answer is still "no".
In cold winter temps there is very minimal moisture that can be contained in the air and this is when condensation would be the biggest concern, cold nights warmer days. For example maximum moisture content a cubic meter of air can hold at 13F is about 9 grams.
A cubic meter would contain 264 fluid gallons and we don't have tanks nearly that big. The amount of potential moisture contained in a half full 25 gallon tank is quite minuscule but I still prefer it empty for the other benefits I mentioned above...
In order for condensation to happen the surface must remain significantly colder than the air. Aluminum has one of the highest heat transfer properties of any of the metals thus when the air temp changes so does the EMPTY aluminum tank and then, no wall condensation.
Can condensation happen in a half full tank, sure, but the volume of water that would get trapped in a filter most likely came from a following sea getting into the vent line or a leaking deck fill fitting not "ounces" or more from condensation.