Why can i only fit 13 gallons in my 19 gallon gas

You can usually only get about 18 gallons in a 19 gallon tank and you likely have 4 gallons left in it when the gauge reads empty

I've got the same exact issue. I too have an 02 Wrangler and often wondered why when the gauge reads empty and in the red area, to fill up she only takes 13-13.5 gal...took it to a mechanic..turns out there is air in the tank and the fuel sending unit it read based on the pressure and not the actual fluid level..

I have 152K on mine and this started happening when I was 90K and I simply ignored it...however it sucks when you're trying to figure out gas mileage.