Fuel tank capacity on 1981 Vette and reserve ?

I put a new Dorman 575 - 080 tank in and it's supposed to be 23.7 gal. tank. I know the original Chevrolet tank was supposed to be a 24 or 25 gallon. After I put the new Dorman in I only put about 4.5 to 5 gallon in and it never registered on the gauge at all. I need to have some exhaust work done on Wednesday so I didn't fill up at the filling station. I did put another 10 gallon in with plastic cans now the gauge registers just a little under 1/2 tank. That's kind of telling me that we have a 5 gallon reserve when the gauge says mt. Is my thinking correct or am I missing something ?

If yours doesn't have a bladder in it then it's not going to register for the first few gallons. Effectively I guess that gives you a reserve capacity. My '73 tank capacity is only 18 gallons so I don't think I have a reserve.

by bladder, if you mean the liner like the original tank had ? no it has no bladder or liner in this tank.

Somewhere in the mid to late seventies, Chevrolet added a safety bladder in the gas tank. Not sure what it looks like so I can't confirm what your old one had. The lack of a bladder in your new one may explain how they got larger capacity assuming that the bladder didn't conform to the entire volume of the tank.

In order to dispose of used fuel tanks in my area they need to be cut in half. When I cut my old tank It had a 1/4 inch think plastic liner in it that was the same form as the inside of the tank itself, nothing else was inside the tank. After it was all said and done I may have spent more money than was necessary. I may not have needed a new tank at all, once I had the tank opened up and the liner out the inside of the tank looked good. The only reason I replaced the tank was after I had it out tipping it from side to side it sounded as if it still had a small amount of fuel in it. I've seen on another web site that the liners did crack and allow fuel in between the tank and liner. It's one of those things that you just don't know until after the fact, and you hate to do it twice.