venting gas tank on ex-diesels - The 1947 - Present Chevrolet & GMC Truck Message Board Network

abig84 · 08-01-2018, 11:13 AM

1986 k30 diesel now has a 400 in it tank does not vent.

I remember after I built this truck drove it to the gas station and the gas tank had a large vacuum. Hissed like crazy after cracking the cap. So my way of fixing it was drill a small hole in the gas cap. Problem with that is can't ever fill it over 3/4 tank or it splashes out. So 10 years later I think it's time to fix it right

So anyone run across this before? Is there a vent on the diesel trucks that is maybe clogged or do I need to change sending units? Probably need to change filler necks also as this 3 inch hole that comes with the cucv trucks sucks for filling up

69heavychevy · 08-01-2018, 09:23 PM

On my truck I got rid of the charcoal canister. On the vent line on the sending unit I added a small rubber hose with a differential vent on the end. I also used a vented gas cap.

69heavychevy · 08-01-2018, 09:25 PM

You might have to switch over to a 3 line sending unit if your former diesel didn't come with one.

abig84 · 08-02-2018, 12:53 AM

Quote:

Originally Posted by 69heavychevy

You might have to switch over to a 3 line sending unit if your former diesel didn't come with one.

I don't think it does , only seen the feed line and the return line coming of the tank.

D13 · 08-02-2018, 06:01 AM

Other way around. Diesels use vented caps, Gas systems vent into the charcoal cannister to store the fuel. When the caps are left at the gas station (easy to do on a dual tank system) un-knowledgable persons replace the hard-to-come-by vented cap with the easy-to-get sealed gas cap. If you don't put the proper emissions system in, including 3 line sender and and cannister, you will need a vented gas cap.

It took me some time on the internet to find the correct diesel cap. My problem was the tank built pressure, then when I had to replace a line it sprayed me down with diesel.

abig84 · 08-02-2018, 01:30 PM

That would probably be the easiest fix but I need to change my filler neck to a normal one
Really don't want to drop the tank

Guessing something like this will work.

part Number - 10819D Green Diesel Fuel Only cap helps prevent accidental fuel contamination Made of sturdy, long-life materials 2-13 16 in. Prevent Pressure vacuum 1-49 64 in. x 2-9 64 in.

https://www.amazon.com/Stant-10819D-...s=stant+10819d

08-01-2018, 11:13 AM	#1
abig84 Registered User Join Date: Jan 2017 Location: wheaton IL Posts: 659	venting gas tank on ex-diesels 1986 k30 diesel now has a 400 in it tank does not vent. I remember after I built this truck drove it to the gas station and the gas tank had a large vacuum. Hissed like crazy after cracking the cap. So my way of fixing it was drill a small hole in the gas cap. Problem with that is can't ever fill it over 3/4 tank or it splashes out. So 10 years later I think it's time to fix it right So anyone run across this before? Is there a vent on the diesel trucks that is maybe clogged or do I need to change sending units? Probably need to change filler necks also as this 3 inch hole that comes with the cucv trucks sucks for filling up

08-01-2018, 09:23 PM	#2
69heavychevy Registered User Join Date: Jan 2007 Location: Garland,TX Posts: 431	Re: venting gas tank on ex-diesels On my truck I got rid of the charcoal canister. On the vent line on the sending unit I added a small rubber hose with a differential vent on the end. I also used a vented gas cap. __________________ 80 C10 SWB Step Side - 350 w/ vortec heads, TH350, 12-bolt 3.73

08-01-2018, 09:25 PM	#3
69heavychevy Registered User Join Date: Jan 2007 Location: Garland,TX Posts: 431	Re: venting gas tank on ex-diesels You might have to switch over to a 3 line sending unit if your former diesel didn't come with one. __________________ 80 C10 SWB Step Side - 350 w/ vortec heads, TH350, 12-bolt 3.73

08-02-2018, 06:01 AM	#5
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	Re: venting gas tank on ex-diesels Other way around. Diesels use vented caps, Gas systems vent into the charcoal cannister to store the fuel. When the caps are left at the gas station (easy to do on a dual tank system) un-knowledgable persons replace the hard-to-come-by vented cap with the easy-to-get sealed gas cap. If you don't put the proper emissions system in, including 3 line sender and and cannister, you will need a vented gas cap. It took me some time on the internet to find the correct diesel cap. My problem was the tank built pressure, then when I had to replace a line it sprayed me down with diesel. __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors

08-02-2018, 01:30 PM	#6
abig84 Registered User Join Date: Jan 2017 Location: wheaton IL Posts: 659	Re: venting gas tank on ex-diesels That would probably be the easiest fix but I need to change my filler neck to a normal one Really don't want to drop the tank Guessing something like this will work. part Number - 10819D Green Diesel Fuel Only cap helps prevent accidental fuel contamination Made of sturdy, long-life materials 2-13 16 in. Prevent Pressure vacuum 1-49 64 in. x 2-9 64 in. https://www.amazon.com/Stant-10819D-...s=stant+10819d Last edited by abig84; 08-02-2018 at 01:41 PM.



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