Diesel Fuel Question

More likely the expansion is with the fuel in the ground but the amount of expansion is nowhere close to what you are experiencing. I have not seen it with my truck but with my gas powered cars it is a lot more difficult to completely fill the tank when it is hot out and there is only a quarter of a tank of fuel when I start. The vapor in the tank interferes with the vapor recovery system in the pump hose and causes it to shut off prematurely. No such system is used with the diesel pumps.

Surely the temp of the fuel you are buying is now warm as opposed to the 57 degree constant of underground?

Thanks for the feedback. I would be surprised if slope were the issue as I almost always fill at the same station from the same pump.

Most fuel tanks are designed with a void area (think the area is about 5% based on name plates on tanks at work)at the top to allow for expansion. That's why the fill cap is on the side and not the top of the semi's fuel tank(s). In the summer if you "top off" a 100 gal fuel tank and park it in the sun it may overflow. The fuel in the ground tanks is around 56 degrees if memory serves. When it heats up to 90 degrees or so on a hot sunny day the tanks have been known to overflow.

Also the diesel engine recirculates unused fuel from the injectors back to the fuel tank warming the fuel. The heat recirculated is enough the tanks will feel warm to the touch even when temps are below freezing.

Typically on a 100 gal semi fuel tank you will have about 95 gals you can put in it and the last 15 gallons/tank are the heal (depends upon who cut the suction tubes) so you will have about 80 gal useable. The heal collects sediment and water to help keep it out of the fuel system.

Slope is a killer..
Last week a friend "ran out of gas", turned out he was low, parked on a steep enough hill to keep the fuel from reaching the pump and..!!!

Don't forget that the tank also expands and contracts during heat cycling

If a metal tank, then it's rates will be higher

Also agree with the possibility of the venting system contributing to this

agesilaus wrote:
Not from the temp change:

Coefficient of expansion

That calculation (see link) shows 1.1 gal/100 gal for a 20 deg F temp change. No way you could be seeing a 5 gal change on a smaller tank.

^^^^^This

Could be lots of things. Remember, just a few degrees of slope on the pump pad will throw the fill rate waaaaaaaaaaaaaaaay off on a tank that big.

Not from the temp change:

Coefficient of expansion

That calculation (see link) shows 1.1 gal/100 gal for a 20 deg F temp change. No way you could be seeing a 5 gal change on a smaller tank.