The fuel gauge on my 86 22re 4runner has done some weird stuff every since I've owned it and now i'm tired of it so I want to try and fix the problem. I can fill the tank full and the gauge will go to full, after about 20 miles it will drop to just over 3/4, and by about 40 to 50 miles it will be down to half a tank. From the halfway point I can drive about 60 miles until it reads empty, from there I can drive for the remainder of the tank which is about 100-110 miles. This probably seems confusing but what could be causing this?