Just doing quick math, I got a long box 00 F350 diesel and it has the big tank. I went 350 miles pulling 15k to 20k loads till the low fuel light came on. Normally I would have stopped for fuel at a station, but I have a transfer tank and just pumped some in to get me through the day.

Anybody got an idea ? I know it will vary, I am guessing 32 gallons ?

 

You're right, it varies, but not enough to worry about. The low fuel light on my '06 SD isn't tied to fuel remaining in the tank, but to estimated miles left. Mine always comes on with 50 miles left. Your '00 may use a different strategy.

Here's the problem with that strategy:

When I tow, I get 10 mpg. At 50 miles, I should have about 5 gallons left in the 38 gallon tank, so it will take 33 gallons to fill.

When I'm not towing, I get 15 mpg. At 50 miles, I should have about 3 gallons left, so it takes 35 gallons.

 

If your's is the same size, I have 42 (supposedly) at the top of the neck. I can go about 50-60 (not towing) after the idiot light. Might be more but haven't tried, the needle was already slightly below the empty line. The most I have ever put in it is 39 gallons.

 

not asking how far I can go, just would like to know how many gallons it will take to fill the take from when the low fuel light comes on. I thought these were 39 gallon tanks, my 99 would normally take 35 gallons after driving home with the light on and then to town.

 

I think you're trying to estimate your mileage, right?

 

It varies, but guess about 30 gal.
Pull up to a fuel station and have at it, then you'll know for sure.