Question on venting a gravity feed aux tank - Chevy and GMC Duramax Diesel Forum
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post #1 of 42 (permalink) Old 08-15-2018, 08:45 AM Thread Starter
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Question on venting a gravity feed aux tank

This pertaining to a 2004.5 LLY. I'm sure I'm overthinking this but never hurts to ask the expertise around here for insight.

Ok I have read enough to see a 'always on' gravity feed aux tank is apparently a bad idea (gravity feed into the fill neck with the RDS 'float' valve that prevents overfilling) It's a cool kit and thought, but apparently a bad idea? and causes the truck to throw codes and such? THAT is unacceptable!! Not going to deal with clearing codes and shut downs to get the fuel gauge working even though I have a Edge CTS and it's easy. iMO any time you throw bad info at a ECM that causes a fault / code,, it is going to cause more headaches and problems with other systems further down the road. PLUS not sure I would 100% trust the float ball system to not overfill and spill 50 gallons of fuel out under the truck / trailer.

REGARDLESS.... I'm wondering if the code is caused by the tank VENT. If I were to tie the in-bed AUX tank vent in to the vent line running from the truck tank to the fuel fill door,, would THAT solve the code issue?????

I guess the question is more ,, does the Duramax fuel system put vacuum to the fuel tank like the gas rigs to purge fuel vapors (and the infamous emissions / fuel cap code)? Is THAT part of what is causing the code when using a 'always on' gravity flow aux tank??

The thought being if the gravity flow is into the fill neck, and the AUX tank is vented to outside air, you could not put a vacuum on the system as the aux tank would always feed and you couldn't get negative pressure. is the lack of vacuum causing the code???? Would that be eliminated if the vent were connected to the truck tank vent line???

Even using a shut-off valve at the AUX tank outlet, should the AUX vent and the truck tank vent be tied together for when you DO gravity feed into the truck tank???

In a race car we drop the vent line over the side of the cell with roll-over valve and a old fuel filter on the end so bugs can't get in,, and vent to the air. The LLY is a little different animal and looking for the SMART way to do this.

(This is the float valve connection kit I have: https://www.northerntool.com/shop/to...5503_200315503 )

2004.5 Silverado CCSB LLY
Sinister EGR delete,
S&B air box and up-sized S&B intake mouthpiece,
CAT converter delete,
ATP 5 stage tune - Edge CST w/ EGT and backup camera,
5" AFE Power full exhaust kit
Airlift 5000# bags w/ on-board remote compressor

Just a nice CLEAN stock truck for towing the toys to the playground with a back seat full of grandkids
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post #2 of 42 (permalink) Old 08-15-2018, 09:05 AM
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Quote:
Originally Posted by MarvDmax04.5 View Post
This pertaining to a 2004.5 LLY. I'm sure I'm overthinking this but never hurts to ask the expertise around here for insight.

Ok I have read enough to see a 'always on' gravity feed aux tank is apparently a bad idea (gravity feed into the fill neck with the RDS 'float' valve that prevents overfilling) It's a cool kit and thought, but apparently a bad idea? and causes the truck to throw codes and such? THAT is unacceptable!! Not going to deal with clearing codes and shut downs to get the fuel gauge working even though I have a Edge CTS and it's easy. iMO any time you throw bad info at a ECM that causes a fault / code,, it is going to cause more headaches and problems with other systems further down the road. PLUS not sure I would 100% trust the float ball system to not overfill and spill 50 gallons of fuel out under the truck / trailer.

REGARDLESS.... I'm wondering if the code is caused by the tank VENT. If I were to tie the in-bed AUX tank vent in to the vent line running from the truck tank to the fuel fill door,, would THAT solve the code issue?????

I guess the question is more ,, does the Duramax fuel system put vacuum to the fuel tank like the gas rigs to purge fuel vapors (and the infamous emissions / fuel cap code)? Is THAT part of what is causing the code when using a 'always on' gravity flow aux tank??

The thought being if the gravity flow is into the fill neck, and the AUX tank is vented to outside air, you could not put a vacuum on the system as the aux tank would always feed and you couldn't get negative pressure. is the lack of vacuum causing the code???? Would that be eliminated if the vent were connected to the truck tank vent line???

Even using a shut-off valve at the AUX tank outlet, should the AUX vent and the truck tank vent be tied together for when you DO gravity feed into the truck tank???

In a race car we drop the vent line over the side of the cell with roll-over valve and a old fuel filter on the end so bugs can't get in,, and vent to the air. The LLY is a little different animal and looking for the SMART way to do this.

(This is the float valve connection kit I have: https://www.northerntool.com/shop/to...5503_200315503 )
I've been using that gravity feed for 5 years without a problem. It does not
set any codes. The fuel gauge will go to empty if you are driving long distances without stopping ( somewhere around two hours or so). But if you stop for a pee break the fuel gauge resets itself. I didn't do anything with the tank vent.

Diesels don't have vacuum (generally speaking), unless it's for Cali emissions on early models.

05 3500 LLY CCLB 4X4
AFE turbo mouthpiece,
Banks Ottomind 6, Banks Speed Brake,
Banks Ram Air intake w/super scoop, Banks Monster exhaust, Cat delete.
Pulling a 15K+ 5th wheel
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post #3 of 42 (permalink) Old 08-15-2018, 05:43 PM Thread Starter
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Hahahah with MY wife,, 2 hours between pee breaks would be a HUGE improvement. In a 250 mile trip she is 'commanding' me to pull over about every 75 miles Takes us FOREVER to get anywhere. But what ya gonna do!

My 04.5 did have the Cali emissions before the 5 level tune and the normal item deletes (Cat, EGR etc) SO maybe the 2 smaller lines coming from the tank to the fill door are just vents???) So the guys calling out codes along with the fuel gauge issue are apparently newer trucks,, (I had to go back and read more thoroughly at the posters sig)

How did you vent the AUX tank? My RDS tank has a vent w/ rollover valve but was thinking of venting it into the fill neck along side the gravity feed. Bad idea?

2004.5 Silverado CCSB LLY
Sinister EGR delete,
S&B air box and up-sized S&B intake mouthpiece,
CAT converter delete,
ATP 5 stage tune - Edge CST w/ EGT and backup camera,
5" AFE Power full exhaust kit
Airlift 5000# bags w/ on-board remote compressor

Just a nice CLEAN stock truck for towing the toys to the playground with a back seat full of grandkids
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post #4 of 42 (permalink) Old 08-16-2018, 06:48 AM
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Quote:
Originally Posted by MarvDmax04.5 View Post
Hahahah with MY wife,, 2 hours between pee breaks would be a HUGE improvement. In a 250 mile trip she is 'commanding' me to pull over about every 75 miles Takes us FOREVER to get anywhere. But what ya gonna do!

My 04.5 did have the Cali emissions before the 5 level tune and the normal item deletes (Cat, EGR etc) SO maybe the 2 smaller lines coming from the tank to the fill door are just vents???) So the guys calling out codes along with the fuel gauge issue are apparently newer trucks,, (I had to go back and read more thoroughly at the posters sig)

How did you vent the AUX tank? My RDS tank has a vent w/ rollover valve but was thinking of venting it into the fill neck along side the gravity feed. Bad idea?
I just vented to atmosphere. I suppose you could vent it to the tank but I don't think you need to.

05 3500 LLY CCLB 4X4
AFE turbo mouthpiece,
Banks Ottomind 6, Banks Speed Brake,
Banks Ram Air intake w/super scoop, Banks Monster exhaust, Cat delete.
Pulling a 15K+ 5th wheel
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post #5 of 42 (permalink) Old 08-16-2018, 07:22 AM Thread Starter
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Thanks. I'll do some more research on the Cali emmission for this LLY and see if there was some vapor purge vacuum pump BS and if so I'll tie into the truck tank vent,, but I'm suspecting when Rob did the tune a lot of that BS went away,, as much as was LEGAL that is ;0
Thanks
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2004.5 Silverado CCSB LLY
Sinister EGR delete,
S&B air box and up-sized S&B intake mouthpiece,
CAT converter delete,
ATP 5 stage tune - Edge CST w/ EGT and backup camera,
5" AFE Power full exhaust kit
Airlift 5000# bags w/ on-board remote compressor

Just a nice CLEAN stock truck for towing the toys to the playground with a back seat full of grandkids
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post #6 of 42 (permalink) Old 08-16-2018, 07:35 AM
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There is NO Vapor purge on the fuel tank on a 04.5 -05 Calif.
Yes, my large tank did cause the fuel light to come on and the gauge went to empty during the first year I had the tank- Guess it finally learned and has not done that in a long time- It did not set codes or affect the running- I just drove on and after 100 miles or so, it corrected itself.

Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.
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post #7 of 42 (permalink) Old 08-16-2018, 08:39 AM
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I've got a 2018 3500 D/A that's equipped with a RDS Aux Fuel Tank/toolbox combo. The fuel tank is 40 gal with a toolbox section on top. On one end of the toolbox is a section that's walled off from the rest of the toolbox and contains the fuel tank fill connection, level gauge (very inaccurate), and a vent fitting that has nipple open to the surroundings. The tank has a manual isolation on the outlet that's outside of the tank and can be reached from the bed of the truck. There's also a solenoid shutoff valve that I control from inside the cab with a toggle switch. If I'm going to use the aux tank I'll have the manual isolation open, but the electric shutoff closed initially. When I see the fuel gauge on the dash come down to the full mark (it's usually pegged out high after filling the tank), I'll open the electric shutoff. The aux tank gravity feeds into the neck of the normal fill connection and i've never had any issue with codes, fuel gauge indications or anything.
It's nice to be able to go a days worth of distance without having to get fuel (although we do stop for other reasons) as it's sometime difficult to find a station I can get the truck & trailer into (and back out of). Can always use truck stops, but they have their own conditions to deal with...

Stock 2018 Silverado D/A 3500 LTZ
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post #8 of 42 (permalink) Old 08-16-2018, 09:42 AM Thread Starter
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Shadow that's actually the tank / box I REALLY wanted,, but just couldn't bring myself to throw $800 (with shipping) at it,, and throw away the cross-bed tool box I already have. So I just added a 45 gallon vertical tank in front and slid the tool box back the 11 inches. I have some thin aluminum diamond plate to make some trim plates to finish out the top of the bedside in front of the bok. (will make it look like it belongs anyways) The 45 gallon tank has the low gravity outlet w/ ball valve, a siphon feed outlet on top, a vent with roll over, locking fill cap and the large pipe fitting for a transfer pump. Your electrical shut-off solenoid is normally closed when key is off, and opens at key on??? Is that correct?

What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.
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File Type: jpg Aux-tank.jpg (40.6 KB, 81 views)

2004.5 Silverado CCSB LLY
Sinister EGR delete,
S&B air box and up-sized S&B intake mouthpiece,
CAT converter delete,
ATP 5 stage tune - Edge CST w/ EGT and backup camera,
5" AFE Power full exhaust kit
Airlift 5000# bags w/ on-board remote compressor

Just a nice CLEAN stock truck for towing the toys to the playground with a back seat full of grandkids
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post #9 of 42 (permalink) Old 08-16-2018, 09:57 AM
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What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.[/QUOTE]

I didn't add a filter between the aux tank and the main tank. I believe that's what the stock filter is for.

05 3500 LLY CCLB 4X4
AFE turbo mouthpiece,
Banks Ottomind 6, Banks Speed Brake,
Banks Ram Air intake w/super scoop, Banks Monster exhaust, Cat delete.
Pulling a 15K+ 5th wheel
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post #10 of 42 (permalink) Old 08-16-2018, 10:23 AM
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Quote:
Originally Posted by MarvDmax04.5 View Post
Your electrical shut-off solenoid is normally closed when key is off, and opens at key on??? Is that correct?
Yes

[/quote]What's everyone doing for filtration between the aux tank and the filler neck??? I was thinking just a small 10micron screen-filter in the 3/8" hose between the ball valve and the fill neck. Don't have a lift pump and filters scrubbing the fuel, just keep good fresh Baldwin filter in the stock filterhead, so want to keep the 'chunks' out of the truck tank.[/quote]

i'm just running a small in-line filter; clear plastic

Stock 2018 Silverado D/A 3500 LTZ
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