Gas Tank not fully filling?

[dastrius]

Hey all!

 

I’ve been dailying my 86 LWB for a month now. 2.5 TBI with the 23.5 Gallon Tank. It has 3 straps and comparing to other images online, I’m 100% sure it’s the 23.5 Gallon tank but there’s always room for mistakes. 

 

When I go to fill up, it only takes 12 gallons and stops there. I usually fill up somewhere between a quarter and an eighth of a tank. I would assume it being a bigger tank, it would take more gas. 

 

I’ve got a brand new pump/sending unit and made sure it was for the correct unit for my sized tank. I’ve also swapped my gauges and it’s done the same thing on both sets.

 

Could it maybe be the sending unit is reading wrong and I’m only using half a tank when it says it’s right above an eighth? Any help is appreciated. 

[eaglescout526]

Heh. So here’s the truth. 
AMC built three tanks for the long bed when the MJ was introduced. 
Diesel

23.5 gas

16 gas. 
The three straps mean nothing for capacity and the three tanks are the same exact size. 
 

If your tank is original AMC equipment, there should be a data plate by the sending unit that will give you a date and capacity. 
 

If it’s been swapped it won’t have that plate. 
 

if your tank is only taking 12gal you probably have the 16 and the wrong sending unit. The difference between the two units is the float arm. The 16 is much shorter than the 23. 
 

What makes the 23 and 16 so different is the filler tube internally. 
The filler tube on the 16 reaches deeper down inside the tank vs the 23.