95 SVX Gas Guage accurate?

I have owned this car a month now. The gas guage goes to E, without the low fuel light going on. When I fill it up it only takes 13 gal. The owners manual says it has a 18 gal tank. Is it normal for there to be 5 gallons while reading E. The owners manual says that the low fuel light comes on when there is about 2 gal. remaining. I never take a chance driving far when the needle reaches E, so the low fuel light never goes on. Does anybody else have this problem??? I am avg 250mi per fill up at 13 gal.