How does a pickup tube work?

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animal

Well-known member
Joined
Nov 24, 2011
Messages
1,160
Location
Downtown Hooper, CO
I've been having fuel delivery problems. I've changed pumps, filters, etc. Today I took the fuel line off the front of the tank (where the fuel pickup ube comes out of the tank. Fuel just dribbled out. WTH? Shouldn't fuel run out in a stream? The tank is new, is shiny inside, no gunk anywhere. The pickup tube filter looks brand new, but when I tried blowing air through the tube backwards, very little actually came out the other end. Is this normal? Do I need a "puller-type" pump to draw the fuel out of the pickup tube? It's about 1 1/2" above the bottom of the tank, and with 5 gallons of fuel on the tank, no fuel comes out at all, not even a drip? I'm lost.
 
Hey Animal, if you can put a clear hose on the tube with the end in a gas can, then lightly pressurize the tank with a rag and a blowgun to see if your getting a fuel stream.
 
I've been having fuel delivery problems. I've changed pumps, filters, etc. Today I took the fuel line off the front of the tank (where the fuel pickup ube comes out of the tank. Fuel just dribbled out. WTH? Shouldn't fuel run out in a stream? The tank is new, is shiny inside, no gunk anywhere. The pickup tube filter looks brand new, but when I tried blowing air through the tube backwards, very little actually came out the other end. Is this normal? Do I need a "puller-type" pump to draw the fuel out of the pickup tube? It's about 1 1/2" above the bottom of the tank, and with 5 gallons of fuel on the tank, no fuel comes out at all, not even a drip? I'm lost.


Ok, Animal, let's look at what you have. I read that you have a "pickup tube", which leads me to believe your pickup is ON TOP of the tank, is that right ? If so, it is a very common way of doing it, I encounter it in the marine business I am in all the time.

If you have that top mounted tube, can you remove it ? They generally unscrew some way. I have seen them plugged up, pinched, and the screen on the end gets plugged and fuel will not flow. Also, NO, fuel should NOT simply flow out of that tube when disconnected, it needs to be sucked out.

What did your tank come from ? I am running an aluminum marine tank in my 27, and it sounds like you might have something like that. Did it ever work OK , is this a new problem or has it never flowed ? Do you have a free flowing vent hose plumbed into the tank ?


Please answer the questions I have asked, and maybe post a picture of your set up. This is a simple one to fix.
 
it's weird...it's obviously flowing fuel, as the car will run 60_65 all day, but runs out of fuel if pushed beyond that or under hard acceleration. I'm wondering if a rotary pump will pull more head and supply more volume under load.
 
it's weird...it's obviously flowing fuel, as the car will run 60_65 all day, but runs out of fuel if pushed beyond that or under hard acceleration. I'm wondering if a rotary pump will pull more head and supply more volume under load.


You haven't answered the questions I asked, Animal. A fuel tank could not be a more simple mechanical device.....it stores fuel, you withdraw it with a pump, and a vent lets air back in to replace the fuel. Very basic.


You will not know if you need a better pump, etc, until you SOLVE THE MOST BASIC questions. Give me what I asked and I will give you your answer. I do exactly this at work 5 days a week, it is a no brainer.
 
From Animal's build thread...

The tank is vented, the cap is vented, the pump is an inline electric. Under much acceleration, it rarely gets to 60 mph without running out of fuel.

I still believe the pump cannot "pull" enough fuel. I understand the pickup is top mounted and I also believe the gravity/siphon effect is weak and/or non-existent.

I'm curious to hear your opinion, Don...

.
 
Don, I just posted earlier, didn't see your post first. The pickup tube, or supply tube, is mounted to a fitting in the front of the tank, about 2" from the bottom. The tube runs from there to approximately the center of the tank, then bends down with a filter on the end nearly touching the bottom of the tank. The tank is a brand new stock replacement 1956 Ford Fairlane tank. The tube is not removable. It is welded to the tank.

The reason I thought fuel should run out is that when submerged, the outlet is below fuel level.

I wonder of the filter is resticting flow somehow. I tried blowing air through it backwards and very little came out. I thought maybe whoever glued it on the tube got some epoxy or whatever over the opening.

I appreciate any help, just didn't see your posts until right now.
 
And there is a free-flowing vent on top of the tube, hooked to a free-flowing vent hose. Fuel won't run out, even with the fuel cap removed.
 
If you can't blow much air through it backwards, it's partially stopped up somewhere. You should get as much air coming out in the tank as you air hose puts out. Either it's kinked at the bend, or the filter could be clogged. I have blown a stopped up filter right off by reverse blowing like that.
 
Ok, Animal, thanks for that info, helps a lot. I have never seen a pickup location like that, but you are right, look at the picture on this ebay ad:

https://www.ebay.com/itm/Fuel-Tank-...m=192509375199&_trksid=p2045573.c100505.m3226


Bamamav is right, if you can not shoot compressed air into the tank (take the cap off first) then there is some blockage in that tube. What is the fitting that goes into that tube, it is hard to tell from the pictures? Is it threads or what ?
 
Don, it's threaded, an inverted flare fitting (same as brake line). A 5/16" brake line threads right into it. I still think there is a restriction at the filter, and as Bamamav says, I may have to blow it off (I tried) or run a gas welding rod through the tube and knock it off.
 
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Any pump should pull fuel out of that tank. There must be a restriction in the pickup tube or the filter. I'd guess it was screwed up by the manufacturer.
 
It's got to be a pretty bad obstruction. My factory Lincoln tank has a 1/4" pickup, and it ran fine at any speed. Can you take out the sending unit and get to the filter end? Might be able to pry it off if you can get to it. Running some rod through the tube is a good idea, too.
 
I can't reach the filter. The sender hole is only about 2 1/2" in diameter, and is at the rear of the tank, on top. It appears the only way to remove the filter is to run a rod through the tube. I'm also going to replace the pump just to make sure.... O'Reilly said they'll swap it out because of the low pressure readings.
 
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I think you and the guys have hit it, there is some obstruction in the pickup tube. Try taking off your gas cap (put a rag over it to keep fuel from blowing out over everything) and then put some compressed air into that hole and see how it flows. At the end, you should be able to turn down the air pressure and air should flow freely.


They put a "mesh sock" over the end of those pickup tubes to keep out debris. They get plugged and crushed, and if you put compressed air to it they will blow off, or at least blow a hole in it. If it goes into the tank it will not cause any problems in there, it just floats around.

I think you are on the right track. Oh, and check your tank vent to make sure it is clear. If it is plugged, the best pump in the world can't pull fuel out as it is airlocked.
 
Animal, I have been doing a little internet snooping, and it looks like the sending unit hole is just about over the top of the area where the tube enters the tank. If all else fails, maybe pull the tank, remove the sender, and look down into that hole to see what is what.


One possibility that entered my mind is, maybe the tube broke loose from the inlet fitting and all you have is an inlet. Remote possibility, but I have seen it happen. That way, your pickup would not be submerged under acceleration, and sucking air.

But try the easy stuff first, you have some good ideas people have provided.
 
Animal, I have been doing a little internet snooping, and it looks like the sending unit hole is just about over the top of the area where the tube enters the tank. If all else fails, maybe pull the tank, remove the sender, and look down into that hole to see what is what.


One possibility that entered my mind is, maybe the tube broke loose from the inlet fitting and all you have is an inlet. Remote possibility, but I have seen it happen. That way, your pickup would not be submerged under acceleration, and sucking air.

But try the easy stuff first, you have some good ideas people have provided.

I had the tank out and looked through the sender hole
before I started the thread. Everything looks shiny and new with no apparent damage. I ended up taking a length of 1/8" gas welding rod and running it through the tube and smacking the filter, trying to knock it loose. I discovered that there is a small tab welded to the bottom of the tank to keep the filter from coming off. I used enough force to bend that tab a little, allowing the filter to move probably 3/16" or so. Either the solid end of the filter was against the end of the tube, or something else was in the way, because my moving the filter resulted in air flowing freely though the tube afterwards. I re-installed the sender, put the tank back in the car, and hooked up the vent hose. I re-did some fuel line routing while I was at it, installed a new pump (O'Reilly replaced the old one because of the low pressure) and filter, took the car off the stands and went for a drive. As I left town, I figured I'd see right away if there was a problem before I got too far from home. I ran it up to about 90, backed off to about 30, jumped back in it and ran it back up to nearly a buck, then drove to the next little town while varying speed and rpm's drastically. Everything worked great, and was still working great a couple hours later when I came home. Now, if the filter doesn't move back and block the tube... :cool:
 

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