Leaky fuel line at sender... how best to fix?

[okartguy]

The '76 I picked up yesterday has a pretty good leak coming from the top of the sender in the trunk... I'd prefer not to turn my pretty new car into a fireball.

There's currently cloth-wrapped fuel line clamped to the brass(?) sender fitting, but it appears that the line is too thickly-walled and flexible, so fuel is seeping out from beneath the clamp. There's also some hard plastic fuel tubing back there.

So, what type of line should be attached to the top of the sender? What material/diameter? Is there a particular brand to look for a vendor to purchase from? There are a bunch of small things I need to do to this car, so I want to make sure they're all done right. TIA-

JJ

[BigDog]

If you are then you got plenty of different diameter fuel line. You will need some to make the outlet on the fuel tank fat enough to seal well with that hose.

Further, there are lots of things you can do regarding fuel plumbing, the #1 is to replace all those rotten old lines with new ones!

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BigDog

'76 2002 All braided stainless fuel supply

[okartguy]

Nope, not a kart racer... that would be "Oklahoma Art Guy," but I see how you might think otherwise! Anyway, I just want to do a clean install of the right-grade stuff, front-to-back.

[Zenon]

That cloth-covered stuff is probably original and if you have much in the way of fuel smells in or around the car, just replace all the rubber lines - it is not that hard to do and best done all at once anyway. Fuel hoses can become porous and sweat fuel vapours rather than outright leak, and hidden under that cloth covering is probably a lot of dried and cracked rubber.

Pretty much all of the fuel hose in a '76 '02 is 8mm ID (5/16" at ~7.9mm is an almost exact match). There is one small section between the fuel pump and the carb (and the return valve if you still have one) that is 6mm (1/4") ID.

The supply fitting on the sender is 6mm and there is a hard plastic 6mm ID-to-8mm OD bushing there. Not sure why that is other than BMW saw a need for a larger supply line at some point but never wanted to re-tool the sender production. If that bushing is toast I don't know what else you could use there - the BMW part number for it (listed as a "sleeve") is 62 16 1 350 285. Just clamping 8mm line down tightly is not good, though you could maybe use 6mm hose and then stretch it over the hard plastic supply tubing that run through the cabin to the engine compartment (that is special stuff, BTW, it melts itself shut in the presence of fire and it never seems to be affected only by age - I sure wish they'd made our dashes out of the same plastic!). Stretching fresh hose 2mm oversize is not bad - just use a bit of oil to help if needed.

Since the system pressures are not much more than 5psi on a carbed car, any decent-quality SAE-rated fuel line will do - using the correct inner diameter size is what really matters. You can buy inch-sized line at any auto supply store - I think you will need about 8 feet of the 8mm(5/16")ID and 1-2feet of 6mm (1/4") to do the whole car, including the return line if it is still in use (and it is not a bad thing to keep in use since the return system prevents vapour lock). You will need to get under the car to replace the rear section of hose in the return line - it is about 4' long and runs over from the driver's rocker over the diff and through that tube in the trunk floor in front of the tank.

BMW dealers sell some excellent BMW-branded hose (probably made by Continental in Germany) that is rated for EFI working pressures somewhere araound 50-100psi, but it is very expensive and overkill for a carb'd car, though definitely top quality if you don't mind paying around 5x more per foot.

regards,

Zenon

[okartguy]

Well, now it looks like the sender itself is leaking, at the base joint where the supply tube comes out. It seeps after the line pressurizes. Anyone dealt with this? Is there any way to repair this short of replacing the sender unit?

[Zenon]

Well, now it looks like the sender itself is leaking, at the base joint where the supply tube comes out. It seeps after the line pressurizes. Anyone dealt with this? Is there any way to repair this short of replacing the sender unit?

The fuel line is not pressurized at that point (unless the tank vent is blocked) - it is under suction. That does not mean it won't leak there, of course. Be sure the leak is not at the hose connection since fuel is great at creeping along surfaces. Also, the sender o-ring could be leaking.

But if you do indeed have a leak at the base of the fitting where it is welded into the sender top, don't dispair. Get some epoxy putty meant for repairing fuel tanks - it will stick to gasoline wet metal no problem. Put a fillet of that stuff around the leaking seam and you will be good indefinitely. I used some on my fuel tank (the seam area had a few rust-induced pinholes) and it has lasted almost four years so far and no hint of a leak yet.

regards,

Zenon