approx fuel left when light comes on???

pnichols wrote:
When the light comes on - how much gas is left MAY depend upon much you put into the tank the last time you filled it.

Not typically, as the light is controlled either from its own float switch or from the sender for the gas gauge. If you put less in when you fill it, it just comes on sooner (the extra gas is of course at the top of the tank, not the bottom). Likewise, if you don't fill but only put in half a tankful, the light will come on at basically the same level. It's not counting miles from the fill-up generally. (A trip computer time to empty display, on the other hand, may work by tracking fuel use since the fill-up and so may be sensitive to how full it was filled.)

Being on sloped ground may affect when it comes on, just as it affects the gas gauge. In some systems where the sender for the fuel gauge is used, rather than a separate float switch or sensor, I suspect the voltage of the chassis 12V system may also affect it depending on how things are designed.

What Wild Bill and others have said - I start looking at 50% when pulling. If I get to 25% I no longer look for something convenient, I grab what I see. Pulling is a ‘no stress’ joy for me; we use off roads, drive speed limit (or set cruise at 64mph on freeway and sit in right lane, don’t push gas gauge, and enjoy the scenery. I enjoy pulling the 5er more than driving without it.

Funny story on idiot lights. I bought a new Mustang in the mid-80s when they first started putting idiot lights on gas gauge. I was so enthralled I had to see it light up. Was driving in Phx with friends from out of state in car and passed several gas stations with gauge on ‘E’ but not light. Friends we’re getting nervous and complained a lot but I was insistent I had to see this ‘new fangled’ Light do it’s job....You guessed it, we were stranded on the side of the road because the factory hadn’t hooked it up properly....

When the light comes on - how much gas is left MAY depend upon much you put into the tank the last time you filled it.

Our Ford E450 55 gallon tank will take about 5 gallons more after most station pumps stop. I can slowly trickle-fill after pump shut-off and get at least another 5 gallons into the tank whenever I fill up. I always try to do this so as to get more travel miles between refills and to ensure we have plenty of fuel supply margin for running the Onan generator should we decide to drycamp.

Ford in tank pumps are better now but I wouldn't run the tank on one under 1/4 because you don't want to let the pump get hot.
Bill

There is a difference between how much fuel is left in the tank and how much usable fuel is left in the tank.

I changed the fuel pump in my '03 E-450. I ran the tank down as low as I dared - the light was on for a long time. I was sure it was very close to empty.

I dropped the fuel tank and siphoned another 6 gallons out.

I put the empty tank back in place (new fuel pump) and poured 5+ gallons in before anything registered on the fuel gauge.

I still have no idea how much usable fuel was in the tank.

Keep in mind the remaining fuel in the tank also cools in-tank fuel pumps and in diesel engines, it cools the high pressure pump.
So you don't want to run it down to nothing on a regular basis.

I tow a car so I start looking for a gas station that is easy to get in and out of and not too expensive at about the half full mark. That way I am not in a rush to get gas.

WILDEBILL308 wrote:
To many variables. I fill up at or before 1/4 tank.If you start looking at 1/2 you won't be in a rush to find "someplace" before it runs out.
Bill

THIS. Really. Running it down to E will bite you in the butt at the worst possible time.

And if you have an onboard Gen, it won't run if the tank is below a certain point. Usually advertised as a quarter but some have found it's more like half.

AND running the tank dry can kill a fuel pump.

romore wrote:
I don't like to push my luck so make every attempt to stay out of that zone. It has come on a few times but I haven't been bitten..... yet.

x2. While it is nice to know how much fuel is left when the light comes on, I think it can be a bad habit to start relying on the 'low fuel light' to start looking for fuel.
I also start looking for fuel at 1/2 tank. Why gamble on running out of fuel?
I've filled up when my tank was at 3/4 because I found a good price along my route.

I use same method and my truck is a 6 gallon reserve and I have pushed it to the fumes. I would go with 9 or just 8 as correct. Easier to count miles so maybe 60 miles unless going up a significant hill.

You really want to know you could carry a 5 gallon can or two and run it fully out. See if you get 60 miles or more. Although not sure it is a great idea to run out of fuel that way.