Mine goes on and off around when I can fill about 13.5-14 gallons in and the most I've ever sqeezed in after driving around on what flet like empty was 15.9 gallons but mostly when I fill up I usually put in 15 gallons when I think it's empty.

 

I go 40miles or so after the light goes on, then I fill up 16-17 gallons. I only once got more than 18 gallons in the tank (I wonder if the tank measured right)

 

I get 15-20 miles from full to 3/4 of a tank. I can't seem to ever get more than13-14.5 gallons in the tank. I have buried the needle and could still only get 14 gallons in the tank. I do believe that the 3rd gen 4runners has a 15.5 gallon gas tank

 

According to all the printed materials it's 18.5 for my '98, but I agree that it seems smaller.

 

Mine used to be 18.5. Now it is much smaller thanks to the tank smashing mod a la Index wall trail.

 

I've gotten near 16 gallons several times but never over and there should always be one or even two gallons that can't be used;you'll never run it truly dry.