How much fuel do you really have left when that fuel light comes on

What size tanks?

 

Every truck is different. Here's an idea, look in your tanks with a flashlight and see.!

 

I don’t wanna find out

 

not much......maybe 20 gallons at most

 

I would also add you really don't want to get fuel levels that low. To start with if you have an APU those fuel reeds are designed to not go all the way to the bottom. This is to avoid getting trash into the APU. Like the previous comment, you don't want to lose prime and take the risk of sucking trash up into the filters. This also applies to reefers too. If you run one out of reefer fuel it's almost a certainty you will have to call out a mechanic to change that fuel filter. Don't do it!

 

2020 cascadia; could only put in 112 gallons when the light came on. 160gal is supposed to be the capacity

 

I have two 100 gal cylinder tanks, and I’ve used up to 170 gallons. In my truck, I have up to 50 miles to go once the needle hits the bottom of the fuel gauge. However, you do not want to do this as you risk sucking in dirty fuel sitting in the bottom of the tanks. I have never run out of fuel, and I regularly fill up my tanks to about 160 gal.

I remember reading a chart where it mentioned that 6 gallons are “unusable fuel” sitting in the bottom of a 100 gal tank. Also, 5% of 100 gal cannot be filled with fuel on cylinder tanks. Rectangle tanks can take in more fuel, but you’re supposed to leave 5% of empty space for safety reasons.

 

I have two 150s. The fuel light comes on and I top off and it holds 230ish.
Tells me that there is 70 still in there.

Problem is that I don't know where the pickup is set and I ain't gonna test it.

I wish I did know.