I’ve noticed on my 2002 GS430 when I’m on empty and fill up gas it only fills up 15.5 gallons instead of the 19.8. Where is the extra 4 gallons?

 

Your fuel gauge is very conservative. Once the fuel indicator light comes on, you presumably still have about 2-3 gallons of fuel left

 

My gas light turns on just below 1/8th of a tank. I've had my fuel level needle right in the middle of the E line and managed to put in just over 61 litres. Typically, I fill as soon as the gas light is on and It usually stops at 54 litres.