It is not uncommon for the diaphragm of mechanical pumps to fail, allowing leakage into the crankcase. Another possibility is that there is a small crack in the fuel line, allowing gas to flow backwards. My fuel lines were rusted and leaking. It never loses its prime after being replaced.

Silky Terrier Dog Breed Playing Aro... Silky Terrier Dog Breed Playing Around

Will a fuel pump prime with no gas?

Turn the key to “On” and then “Off” a few times after you’ve refilled the tank to prime the fuel pump after you’ve just finished filling up. When running low on gas, it’s a good idea to prime the fuel pump to remove any air that may have gotten into the lines.

Can a fuel pump fail suddenly?

Unpredictable and sudden fuel pump failures are the norm, with little warning to the driver. In addition, the likelihood of a fuel pump failure rises with the number of miles the vehicle has been driven.