Pressure in Diesel fuel tank 2015 3500 Silverado

Just finished installing an up to 20 Gal/hour pump on my Aux Tank. Went off to Wally World to fill up the Aux tank and ran the fuel pump while there.

Thought I would see what it sounded like to have fuel pumping in so I opened up the filler cap. Got a good sized whoosh of air. Listened to the fuel being pumped in for a minute and then put the cap back on.

Cracked it open a few minutes later and got another whoosh. Those of you with experience with a pump like this.....

1. is this pressure build up a concern?

2. Is there a relief valve somewhere that will relieve the pressure if it gets too high?

Thanks,

Did you install some sort of a vent line adapter?

Peace
Dave

Does your Aux tank have a vent on it ???

Cookie...standard setup on truck. I do know when I put in original grav feed I believe there is a "vent line" right beside Fuel inlet line. I am still using the gravity feed system set up with pump.

John...yes aux tank has vent but question is about pressurizing trucks tank....but might not understand where you're going.

Me and Dave were thinking the same thing, tank not venting

I think he's saying his OEM tank is being pressurized. Maybe the 20 gal/hr pump and the OEM vent have a conflict????


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Their all tied together now maybe the rollover valve shut off the vent. That's why I took my pump off I pumped 30 gal down the garage drain.

Think you need something like this.

Read all about it HERE. Look about 2/3's down the page.

Peace
Dave

Nice find Dave

Gary, is the fuel cap vented or none vented?? It should have a vented cap. Sounds like your pump is creating a vacuum when on. My tank came will a non-vented cap and would not gravity feed unless the cap was off. Found a nice chrome plated vented cap a NAPA.

Thanks all....I think this morning I have some answers....but there is still a good question at the end.

I ran a little experiment this morning:

1. cracked open the gas cap (Bob I am fairly sure it is vented as it has a little grid area inside and I have seen on the web they say this is were the vent is at) and heard no sound of air escaping.

2. pumped fuel for 10 minutes putting about a 1/16+ of a tank....well at least that's how far the gauge in the dash moved.

3. stopped the pump and cracked open the cap....got a little whoosh. Put the cap back on.

4. Pumped gas for another 10 minutes and then turned the pump off.

5. Just went out (an hour later) and cracked open the cap.....no whoosh.

So what it would seem that when filling the OEM tank my pump can push in more fuel than the "air" it displaces can escape out through the vent. At least my conclusion.

But it still begs the question, to those of you who pump your fuel like this while driving, do you run the pump for 15 minutes and then turn it off to equalize the pressure through the venting system....in my case seems to be the cap?

Or....do you just not worry about it as no damage has ever been done to your OEM tank filling it up with the cap on via a pump?

I did notice in my web investigation that it does seem there is a pressure sensor on the OEM tank. So why it is there if pressure is not a problem.....or maybe it is there if it senses a vacuum?

Gary, filling the OEM tank is different that filling with your AUX tank and using the pump. Your OEM tank vents as you fill it (pushes out air). With the OEM cap on the OEM tank filler neck...it does not vent. Hence, the only venting is through the AUX tank cap/vent. Mine being gravity feed still will take 10-15 minutes the fill the OEM tank through the fill hose that comes with the AUX tank. Leave the AUX tank cap off and use the pump and see what happens. If there is a change...."no whooose"....go to NAPA. Buy a vented cap (about $8)....put it on and see if you still have the same problem. Make sure you take the cap you have to match it up. I just took a hand full of caps out to the truck, tried them until I found one that fit correctly. I may be wrong but...bet not. Remember your dealing with EPA standards for emissions.