Underbed gas tank very slow to fill. Any ideas for venting, etc?

[Old Yeller 1970]

Way back before I restored Old Yeller I removed the cab gas tank and put a Blazer tank under the bed. Since I have a step side I routed the donor Blazer's fill neck out the rear of the left fender. IIRC, the tank came off a 71-72 body but was missing the gas cap. The 70 cap from my in cab tank didn't fit. When I bought a new cap I ordered a 71 cap but it didn't fit either. Ordering a 72 worked and has been on there ever since. (Who would have thought three different years would have three different gas caps?)

The only issue with it I've never resolved satisfactorily (this has been going on for years) is filling the tank is slower than pond water. I have to hold the nozzle sideways and at just the right angle and barely squeeze the handle to let the fuel tickle in. Putting the handle on the slowest setting usually is too fast and it will back flow out the inlet.

There are no restrictions in the fill line. There is one vent line that comes from the tank up to the fill neck. It has no restrictions in it. During the restoration I replaced the OEM tank with a poly tank. The poly tank has extra ports for hoses etc and I added an extra hose barb and hose and ran it up inside the fender next to the fill neck, put a bug screen over it and tied it off so it vents directly to air. I'm not at all satisfied with it being like that. It did help some but not much. It's possible the angle of the fill neck on Old Yeller is at just enough of a different angle than a Blazer to cause my problem. It doesn't look like it should be but I can't rule it out.

Reckon I'm going to have to live with it or is there hope for me?

Here's what it looked like before the resto and adding the second vent line.

[Old Yeller 1970]

I realized after posting that the previous photos don't show the setup as currently installed, mainly because of the obvious arch in the fill line as it goes over the frame. Thinking that might be the problem I came up with two 1 1/2" 45 degree fittings that let it turn and make more of straight shot without kinking the hose. I just took the two photos below.

[TrkEnvy]

I was gonna say where the filler hose moves over that hump.. I would think that the direction change up is gonna slow the incoming fuel down and if its moving slower than whats coming out of the fuel nozzle its gonna back fill and your gonna have to pump slow. Did your fix help at all?? It still looks like the fuel has to travel uphill..

[chevy72pu]

I have the same problem with mine. It has a '90 sportside bed and the po had moved the filler neck from the front of the fender to the back and down to the blazer tank between the frame rails. It had the "hump" in it to. I tried new vent lines, new filler hose and even notched the frame rail to no avail. Finally cut a hole in the bed and fed the filler hose straight down to the tank using a "cool cap" opening. Still have trouble pumping it slow enough to keep the nozzle from shutting off. IMHO the intake tube on the blazer tank is too small to take the fuel any faster. I know this doesn't fix your problem, but at least I feel your pain. LOL

[Old Yeller 1970]

Originally Posted by chevy72pu

Finally cut a hole in the bed and fed the filler hose straight down to the tank using a "cool cap" opening. Still have trouble pumping it slow enough to keep the nozzle from shutting off.

I've wondered if that would resolve it at least now I know that's not a solution. I wonder if the Blazer guys have trouble with this.

[Old Yeller 1970]

Originally Posted by TrkEnvy

Did your fix help at all?? It still looks like the fuel has to travel uphill..

It's level with the truck now but it didn't really help. Making such a sharp turn may be the problem although there had to be a turn for it to get into the tank when it was on the Blazer.

[chevy72pu]

I wondered if they have trouble with it too. Maybe you could post this over on the Blazer forum and see what they say.

[Palf70Step]

Have you tried an extra vent on the opposite side of the tank to help the air escape during filling? I seem to remember most folks doing that and having a marine type or motorcycle vent stuck up in the passenger side fender wheel.

[bigguy69]

i have the same problem with mine.the filler it is in the bed also. i would like to find a solution also.

[Old Yeller 1970]

Originally Posted by Palf70Step

Have you tried an extra vent on the opposite side of the tank to help the air escape during filling? I seem to remember most folks doing that and having a marine type or motorcycle vent stuck up in the passenger side fender wheel.

No, but that is a possibility. There is another place for a fitting on the passenger side of the tank. And I hadn't thought about a marine or motorcycle vent. I'll look into it.

[The one]

I just did this swap on my 1971 chevy 4x4 and have had no problems filling the tank. My tank came from Brothers Trucks (http://www.brotherstrucks.com/prodin...number=GTPDS72) and has two additional vents on the sides of the tank. I connected both of them with aluminum fuel line and ran a gas tube vent (http://www.motorcycle-superstore.com...With-Tube.aspx) inside the passenger side wheel well. Just make sure the vent is higher than your fuel filler and you should have no problems.I also connectd the vent line that runs up to the fuel filler neck.

[kevmic28]

It looks like you have a vent line capped off in the pics. This may be your problem. Also from what I can tell the vent that is capped close to the filler tube is the one that should go back to the filler tube. try reversing your connections.

I have 2 vent lines on my blazer tank. One goes back to the filler tube and another is just to a filter for venting.

[trz1000]

FWIW, I have a 72 Jimmy and do not have the problem. The Jimmy fills better than my (now gone) 71 c-10 with the tank in the cab.

In Oregon you can't pump your own gas, apparently it's a way to create jobs but it really just slows down the fuel sale process. Anyway, the petroleum injection technicians always struggled filling the truck but have no trouble with the Jimmy.

[kevmic28]

Only time I have issues with filling my truck is when I pull into one of the stations that has those damn rubber tips on the hoses, mostly in the bigger cities. They are so big that the nozzle will barely fit into the filler tube.

[Lemield]

I have a factory aux tank on my C20 and it fills REALLY REALLY slow too. Interested to know if you find a solution.

[71meangreenc10]

I have a plastic tank and its vented out the wazzuu, still fills slow, I am going to try a metal tank and see if it makes any difference....


Smitty

[Old Yeller 1970]

Originally Posted by The one

I just did this swap on my 1971 chevy 4x4 and have had no problems filling the tank. My tank came from Brothers Trucks (http://www.brotherstrucks.com/prodin...number=GTPDS72) and has two additional vents on the sides of the tank. I connected both of them with aluminum fuel line and ran a gas tube vent (http://www.motorcycle-superstore.com...With-Tube.aspx) inside the passenger side wheel well. Just make sure the vent is higher than your fuel filler and you should have no problems.I also connectd the vent line that runs up to the fuel filler neck.

Thanks for the link on the vent. I'll buy some and give them a try.
Where did you get the aluminum fuel line?
My poly tank looks exactly like that metal one. I wonder if it's possible that otherwise identical tanks but of different manufacture can affect the fill rate?

Originally Posted by kevmic28

It looks like you have a vent line capped off in the pics. This may be your problem. Also from what I can tell the vent that is capped close to the filler tube is the one that should go back to the filler tube. try reversing your connections.

I have 2 vent lines on my blazer tank. One goes back to the filler tube and another is just to a filter for venting.

In the first set of photos it was capped but it's not now. The one that is closest to the filler is the one I have run up inside the fender with a bug screen tied over it. You can barely see it in the second set of photos.

Originally Posted by 71meangreenc10

I have a plastic tank and its vented out the wazzuu, still fills slow, I am going to try a metal tank and see if it makes any difference....


Smitty

Good luck let us know how it turns out. FWIW, my original metal tank filled just as slow as my poly tank. If you buy the same tank from Brother's as The One did, it would be interesting to know if it cures your problem.

[kevmic28]

The one next to the filler should be the one going back to the filler.

[DaBigKahuna]

Originally Posted by The one

I just did this swap on my 1971 chevy 4x4 and have had no problems filling the tank. My tank came from Brothers Trucks (http://www.brotherstrucks.com/prodin...number=GTPDS72) and has two additional vents on the sides of the tank. I connected both of them with aluminum fuel line and ran a gas tube vent (http://www.motorcycle-superstore.com...With-Tube.aspx) inside the passenger side wheel well. Just make sure the vent is higher than your fuel filler and you should have no problems.I also connectd the vent line that runs up to the fuel filler neck.

How much does that tank hold?

[71meangreenc10]

I have two of the vents on the plastic tank going up to the filler neck and the other side is vented to the charcoal canister. Do you think I need to take on of the vents off the filler and run it higher than the filler neck?

Thoughts.......

Smitty

[OldSkool71]

I have a metal tank and it is a pain to fill. Fills from inside the bed. Haven't had a chance to get under there and really check it out. Keep us posted. When I get under mine I will post some pics. And see where we are at.
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[RRR18]

Mine is hella slow filling too. It gives me a chance to talk to a lotta people about how much they like the '67 to '72s at the gas stations though. Ha. This is only pic I have of the filler. Mine goes from the filler to a 90 and then straight to the tank. I have to check my vents.

[Old Yeller 1970]

I just realized something. I don't know if this is causing all our trouble but if gas is able to get in the vent line and then sit there (which it could potentially do on mine) it will block the ability of the air trying to escape during fill up and make the tank slow to fill. I'm out of town on business but as soon as I get back, I'm going to take the vent lines loose at the tank and see if there's any gas sitting in there.

[The one]

I bought the fuel line from Speedway motors (http://www.speedwaymotors.com/Alumin...Line,1633.html) they have 1/4", 3/8" and 1/2" line I used the 3/8 inch fuel line and it worked out fine. The brothers tanks holds 21 gallons of gas.

[Old Yeller 1970]

Update: I pulled the two vent lines loose on my rig and neither had gas in them. I checked them out real well and air flows freely through either one. I'm going to say that ventilation is not my problem at this point.

After considering TrkEnvy's observation I rechecked the angle of the fill line and it was going uphill slightly. I took the filler line off and notched the side of the bed right above the fill line to allow it a better angle and reassembled it. I haven't been to the gas station yet. I may also lower the gas tank too. Right now it's tight up against the bottom of the frame but with some kind of shim it could be lowered 3/4" before the fill line contacts the top of the frame allowing an even better angle.

While I had the Blazer fuel inlet out, in the interests of science and making sure all my bases are covered, I took it to town and filled a gas can through the inlet. My thought was to make sure I didn't have any problems with it. I started with the fuel nozzle at the highest setting and gas immediately blew back out the inlet. I put it on the lowest setting and set the nozzle in the inlet like you normally would and it did fine. If I can get it to work like this on the truck I'll be tickled pink. Usually I have to hold the nozzle open so it barely trickles out the least amount of gas and I have to hold it side ways or gas spills out.