Insides of a 55 fuel tank

[Jeff Rosansky CLC #28373]

Hello all,
We are doing some diagnostic work on the fuel system in our 55. I have about half a tank, give or take, and I have removed thr fuel line from the outlet on the driver's side. I was expecting fuel to come out, but we only got a dribble. As you know, that outlet is not at the lowest point of the tank. I assume there must be a pickup tube in there that goes to the bottom, correct??
I only got a small dribble out of the outlet. I thought it mite be plugged so blew some air back thru it (low pressure, about 5ish psi and the cap was off).  I did hear the fuel bubbling in there. When I blew back thru it, the dribble stopped completely for about a minute and then it resumed the same amount.
So, how much output should I expect with half a tank and the line off? I'm concerned there may be a hole in the pickup tube or some other reason I'm not getting much fuel out.
We did have the tank cleaned when we woke the car up about 5 years ago.
Thanks
Jeff R

[Lexi]

Hi Jeff. Just something to consider, but I wonder if your gas tank brass ferrule fitting is stuck in the outlet side of the tank-perhaps even twisted sideways and thus partially blocking the line? Almost positive the '55 Cadillacs came equipped with them. Clay/Lexi

[Jeff Rosansky CLC #28373]

Hi Jeff. Just something to consider, but I wonder if your gas tank brass ferrule fitting is stuck in the outlet side of the tank-Clay/Lexi

Very good thought. However I don't have that anymore. I have an electric fuel pump back there with a line from the tank to the pump. I was able to find a different fitting when we did that setup.
But excellent suggestion, thanks.
Jeff R

[V63]

Maybe try this?

This takes some degree of mechanical artistry do not to over pressurize the system, also cognitive that the medium is gasoline.

With a damp towel, seal the fuel filler (gas cap off) with the towel around an air nozzle from a Shop compressor....carefully pressurize the whole tank such that a Very healthy stream of fuel Should exit the outlet.

That's a test to verify the internal pickup tube is at least clear.

Further,  clamp To the fuel line outlet,  a section of hose, such to creat a siphon situation where the fuel is streaming into a gas can. This 'should' effectively  empty the tank ...however if the internal tube is compromised the fuel will STOP flowing once the flaw is allowed to compromise the siphon. This is the point too where the fuel pump can no longer draw fuel.

[Jeff Rosansky CLC #28373]

Good idea. I was going to try siphoning it today but I hadn't thought of pressurized it from the top end. Thanks for the idea.
Jeff R

[fishnjim]

With a 67 year old tank in unknown condition, applying pressure is a recipe for disaster.   Better to take the tank down after you drain as much as you can and open the top where the level sender is and inspect with a light or camera.   (I use a grounded pump and container for this, sending the tubing down the inlet.)
One larger piece of rust or other debris will dam around the outlet and restrict flow as it gets carried along.  Blowing it back only delays the next "dam"*.   
It only has to flow 3-4 gallons/hour, so it's normally a slow go.  The ID of the bulkhead is restricting also.  Some tanks come with a drain plug, but not many.  Usually they're froze too.

* - I was traveling in my RV once towing to a state tournament and had fuel line pluggage that stop me cold on the interstate.  The wrecker guy came and blew the line back to the tank.  It started, he left, we went about 10 miles and were stranded again, so don't bother blowing back into the tanks, folks, it's not going to accomplish a miracle.  I had to drop the boat at the repair station and ride with a fellow competitor, then once we arrived, drove that vehicle back to pick up my boat.  I didn't get much sleep and didn't do well.  One of the other club members, now deceased, offered his tow and towed me back home after.

[J. Gomez]

Jeff,

I'm remote so sorry for the typos. 

I believe the '55 has the same set-up as the '56, the pickup tube inside the tank is roughly 12" and it is flatten at the end, so it could well be plugged up.

 You can try to fish a small rod inside the tube and see if you can clear the line. Just be careful in doing this with a tank with fuel.

Good luck...!

[walt chomosh #23510]

Jeff,
  The PO of my 1955CDV sent the tank out for flushing and "sealing". THAT almost cost my wife and myself lives...not to mention an approaching car coming at a high rate of speed in the dark along rt66! When I got the car home I found out that couldn't even shove a coat hanger into the tank's outlet. I had a shop open up the tank (don't do this at home!)and I proceeded to clean it and then tig weld the top back. In my case, the "sealing" of the tank had all come loose plugging the outlet. A guy should be able to remove the tank sender unit and peek inside. Good luck and work safely!....walt...tulsa,ok 

[Jeff Rosansky CLC #28373]

Thanks guys. I brought a long piece of safety wire that I will run thru the pickup. I only blew back to see if there was a change which would have told me I needed to drop the tank. I will try to siphon some fuel today out if the outlet. I have a piece of clear tubing that I will attach and siphon gas up. Then I will do the old straw at McDonald's thing by putting my thumb over the end. I figure if it holds the level then the pickup tube is submerged and doesn't have any holes.
I had this tank boiled out 5 years ago.
I just want to see if I am on thr right track.
I'll report back.
Jeff R

[The Tassie Devil(le)]

* - I was traveling in my RV once towing to a state tournament and had fuel line pluggage that stop me cold on the interstate.  The wrecker guy came and blew the line back to the tank.  It started, he left, we went about 10 miles and were stranded again, so don't bother blowing back into the tanks, folks, it's not going to accomplish a miracle.  I had to drop the boat at the repair station and ride with a fellow competitor, then once we arrived, drove that vehicle back to pick up my boat.  I didn't get much sleep and didn't do well.  One of the other club members, now deceased, offered his tow and towed me back home after.

Years ago, I had a similar problem.   Would drive a distance, and the car would stop for no reason.   Called the RACT (Your AAA) and eventually it was traced to a fuel line blockage, so the mechanic used compressed air to blow the line clear, and all was good.   Off I went, and drove back home.

Next day, did the same drive as previously, and yes, had to call out the RACT, who blew the line backwards, clearing the obstruction.   Well, happened twice more and each time, after driving a shorter distance.

Finally bit the bullet and dropped the tank, and inside found lumps of congealed rubber and the remains of a rubber hose.   

Verdict was that someone prior to my ownership of the car must have tried to syphon petrol out of the tank, and accidentally dropped the hose inside the tank.   And yes, Rubber does decomposer in petrol, but it takes a long time.   A very long time, and as the decomposing created smaller and smaller pieces, they got that small that they started to fit inside the fuel line.

If it had been a neoprene hose, then it wouldn't have been a problem.

Bruce.

[Jeff Rosansky CLC #28373]

Well, I put a rubber hose on the tank outlet and sucked up gas. Brought it above the level of the tank and it held. I'm taking that as the pickup tube is intact-at least at the level of the fuel anyway.
Our problem happened a couple times after driving it for a bit. The cap is vented but maybe thr vent is plugged.
Thanks all for your help.
Jeff R

[CadillacFanBob]

Jeff,

I had a friend that the metal pickup tube for the sending unit had corroded apart and would not suck up fuel because the corroded area was up higher in the tank, so he still had a lot of fuel in tank, but would die out from lack of fuel being picked up through the metal pickup tube.

Just my thoughts

Bob

[Jeff Rosansky CLC #28373]

Jeff,

I had a friend that the metal pickup tube for the sending unit had corroded apart and would not suck up fuel because the corroded area was up higher in the tank, so he still had a lot of fuel in tank, but would die out from lack of fuel being picked up through the metal pickup tube.

Just my thoughts

Bob

That was my thinking too which is why I did the soda straw test. There still may be an issue eith mine.
Thanks for the thought.
Jeff R