What do I do with the vent port on my sending unit?

What do I do with the vent port on my sending unit?

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. 

  1. Reduced fluid fill volume
  2. Reduced power levels at high throttle
  3. Pump starvation and/or loud fuel pump
  4. In extreme cases the tank may collapse
  5. 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. 


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1 comment

I I have 1970 Chevelle with a 550 HP Big Block has stock Mecanical Carter fuel pump with 1/4 inch return line . I want to go to a more Gallons per hour fuel pump but they don’t have a return . I have been told I can’t run a bypass regulator with 1/4 inch return . I would like to keep my return line . What do I do ?

Daniel Peters

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