Fuel Tank Vent

[h67st]

Here's a question--I bought new fuel tanks and vented caps. Do I need separate vents for the tanks, or will the vented caps do the job?

[mechohaulic]

my thoughts and only mine . if the new tanks are on the ground ready for install , I would put top vents in. 1- hot weather and fuel expands hope it doesn't run down tank. from vented caps. . 2 with top vent you can add tad more fuel . 3- old tanks have vents on top that can be transferred? 4 have seen tanks seeping from vented caps  possibly they were over full

[Joey Mack]

I would also put seperate vents in,  There are some that have a check ball in them to allow for expansion, but keep stuff from being sucked in when the fuel cools off over night..   You should be able to use a 2000 model CH-613 if you need to find a part number, or maybe you have a parts guy at a local parts house that knows what you want...  Jojo

[mechohaulic]

good vents with the check ball actually have duel purpose. not only keep crap out but also if the fuel expands ; starts out the vent it will close the vent stopping fuel from leaking. at $6.00 plus don't splill a drop.  or go the red neck cheapo valve 90 degree fitting with hose attached. parked on a slant and all the fuel runs over to low tank on down the road. hello EPA 

[Freightrain]

I kept the stock vent lines on my new Alumitanks.

[70mackMB]

The Volvos we run have a check valve vent line on them that sticks closed some times. Have had it happen a few times, the fuel doesn't cross over and the draw side tank goes dry. And the fuel gauge is in the tank with fuel left in it! Go figure.   .....Hippy 

[mechohaulic]

In simple  times a vent was nothing more than 1/4 in COPPER tubing off a 90degree fitting out few inches and had a loop  . gone is the copper tubing and simple design.

[doubleclutchinweasel]

On 11/19/2022 at 9:25 AM, mechohaulic said:

In simple  times a vent was nothing more than 1/4 in COPPER tubing off a 90degree fitting out few inches and had a loop  . gone is the copper tubing and simple design.

That's what mine had, and they worked great...as long as you kept the mud dauber nests out of them!  That design worked for decades.

[Vladislav]

The main need of tank vent is allowing athmosphere air to go in for compensation of the space of fuel consumed by engine. If air doesn't come you get vaccuum in the tank and it's as deeper as longer you drive and more fuel taken off and burned. At a certain point athmosphere would press sides of the tank making it looking like empty beer can after you grab it tight. 

I haven't seen truck tanks ruined that way (trucks are not my business) but there were plenty of car stuff and that brang me some good money a few dozen times. So all in all the vent is an important thing and doubling it wouldn't be bad. But in theory it must be enough having just one in the cap.

At the same time there's no real need to release excessive vapour pressue built up in a tank on a hot sunny day. Only for reason to not put sudden shower on a driver at the time he opens a cap... But normally it doesn't happen, just only "phooff".

German cars (I mostly deal with) had straight tube for breathing before 1985. Than after that they got equipped with a whole system including char coal absorber, a few control valves and a net of tubes. I have never investigated its principal of operation completely but in general it allows outside air to come in when needed (particuallary when engine is running) and not allowing vapours to go out for protection the environment. Life is good as long as all functions well. But once something goes wrong or a body man assembled the lines incorrect fixing an exident damage the tank gets smashed on the 1st or 2nd day of driving.   

[mechohaulic]

another angle to be considered is a tank without a vent (or2) would not only create a vacuum in the suction tank ;;like those ridicules new style fuel cans ; but with out a vent (or2) the returning unused fuel from an engine  which is very warm would create pressure in the return tank and bottle neck an engine,or in days of ole when running a cummins with restricted fuel return :: horsepower increased😃LOL   if you didn't have access to a different fuel button.

[h67st]

I got to looking at one of the caps; the large cone-looking thing on the left will let excess pressure out, while the small hole to the upper right has a ball and spring that will let air suck in when needed. I'm going to run without an additional vent for now and see if I run into any problems with it.