Whistling from fuel tank

[scboolitcaster]

As I was doing my walkaround this morning, I heard a whistling sound coming from the area of the fuel tank.

So I started wiggling lines around at the top of the tank, and discovered one was disconnected.

This one:


I grabbed a wrench and threded it back in and tightened it, but I don't think that's where the whistling was coming from. (What does that line go to, anyway?)

I was headed to work and didn't have time to mess with it further. I guess I need to get under there with a squirt bottle of soapy water and figure out where that whistling is coming from. I'm no mechanic, but I'm reckon I shouldn't be hearing that.

 

[Wildchild467]

Does it make the sound with the truck off? It could be our electric fuel pump located inside the tank. Your squirt bottle will not help because one line is fuel pressure and the other is return. If they were leaking, you would see fuel leaking.

Check your drain valves on your air tanks to make sure they are closed. sounds can echo and appear somewhere that they are not.

 

[scboolitcaster]

When I remove the fuel cap, should there be a vacuum?

I think the line that was off might be the return. Is the return a small copper line?

I had to run an errand during lunch and undid the cap to check fuel level. A lot of air sucked in and the truck seemed to run better. I wonder if the return is restricted?



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[scboolitcaster]

This just keeps getting stranger and stranger. Looking at the parts manual for LDS 465, the return line should be rubber. So the one that wasn't tightened down was the supply I guess.
I wiggled it and it literally came loose in my hand.

Doesn't make sense. As far as I can see there's only two lines.

 

[daytonatrbo]

I thought the return was the one towards the front of the tank, and the little one was the vent.

It sounds like your vent is plugged.

 

[Ferroequinologist]

Sounds like the small line is the tank breather, should run up to the firewall near the air cleaner if I remember. If you tightened it up and now have a vacuum problem, my guess is the line is plugged up. I never touched anything on the tank so it must have been that way for awhile. I would take an air hose and blow through the line from the tank up to make sure it is clear. The return line ties into the tank at a different location than the pump flange, near the back corner of the cab I seem to recall.

The fuel pump might be making the whistling. Try it by turning on the pump an not starting the truck.

 

[74M35A2]

Smurfs

 

[scboolitcaster]

Thanks for the help guys,

I need to get under this afternoon anyway to tighten up the fittings by the IP (have a slow drip now). I will trace the lines and figure out what's what.

 

[Floridianson]

The vent line ran to the road draft tube if I remember correct.

 

[bonedoc]

That is the tank vent line. Mine was actually routed under the truck where it tied together with the airpack vent line, then up to the firewall.

 

[scboolitcaster]

It rained. My work area is now mud.

I hear the whistling sound with the pump on and engine off.

I'm gonna try blowing out that line.

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[Floridianson]

If I remember the fuel tank and the master cylinder were connected then to draft tube. The MWO was to disconnect the master and run it up the firewall. Never know who,what ,when or where someone did something that can not be correct on these trucks. I have seen more fuel filters with the inside hardware incorrect and the filter not filtering. Got to check everything when you get them.

 

[scboolitcaster]

I traced the line to the slobber tube. At first I thought it was totally plugged. But it's not. I can hear and feel air at the end of the slobber tube when I force air through.

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