What to do with the vent port on a fuel sending unit.
We get asked very often what the purpose and what to do with that 3rd vent port on fuel tank sending units.
What does a vent on a fuel tank sending unit do?
A vent is an important part of your fuel system as temperature changes occur either from outside environmental factors or the heat introduced into a system from operation of the fuel pump the fluid and vapors within a tank expand as fuel system temperatures increase and retract as the fuel system temperature goes back down.
Can I cap off my fuel system vent?
NO, you must allow the fuel system a way to relieve system pressure and equalize the pressure with the surrounding environment. The only way to get around utilizing the fuel sending unit vent is by running a vented gas cap in it's place but at the end of the day the system needs a vent.
What do I do with the vent port?
On a factory system this vent likely vented out to a charcoal canister which kept fuel vapors from stinking up the garage. Most aftermarket builds have had this system removed entirely in which case you can install a roll over valve onto the vent port. A rollover valve will prevent fluid from leaking out of the gas tank in case of a vehicle rollover. See HERE for our rollover valves.
Symptoms of a clogged fuel tank vent.
Some symptoms that you may experience if your vent is blocked on your fuel tank.
- Reduced fluid fill volume
- Reduced power levels at high throttle
- Pump starvation and/or loud fuel pump
- In extreme cases the tank may collapse
- No start/no prime on the fuel pump
As you can see something as simple as a vent can cause a number of issues with your vehicle.