Oh don't do it often, but once or twice a year run down to single digits with a fuel can in the trunk. The only way to know if the siphon is working. That said less than an hour your can pull the left side sending unit to verify the seals are good if they are still in good shape you could drill a couple small holes an put some stainless screws to prevent the o-ring from popping out. I will show that the next time I have the siphon side out.
I can't speak for diesel but with gas in most of America, one of the few few few benefits of polluted gas (E10) for non corn farmers is that the alcohol absorbs the water and removes it.

The x5 fuel system circulates the fuel so fast that no fuel it all gets left behind it's totally mixed homogeneous. If there are any impurities they will get sucked away and into the filter. Due to the rapid mixing I'm sure that any water will also get hold in slowly a little bit at a time


Sent from my iPhone using Tapatalk Pro

Yeah, water and petrol (and esp. E10 etc.) will "mix" but not so with diesel - there's no way to get them to mix and if water gets into the mechanical high pressure (HP) fuel pump, it will destroy the HP pump pretty quickly, galling the HP pump faces due to the low lubricity of water vs diesel. :wow:

The E53 3.0D has at two fuel filters and two electric fuel pumps before the HP pump so water getting into the system can render a vehicle useless (not cost-effective to repair).

For some reason, I feel like I need to qualify this statement. :dunno:

The bit that is important here is not that the right side stops are 1.4L, it's that the left side continues to drop AFTER the right side stops at 1.4L. And that's the key, as andrewwynn has been saying. And has also been stated, you can be doubly sure the siphon is working well by letting the left side run down until virtually empty, as verified by the BC readings.

Andrewwynn - thanks for your work on this. My son's car has approximately 150K miles, and it seems as if it would be worth a bit of preventative maintenance to both 1) replace the pump in the fuel sender and 2) replace the o-ring/washer in the siphon unit. If I understand things properly, you also placed a zip tie so as to prevent the plastic connections from getting skewed? I think I understand about the teflon tape to make a slip connection tighter, but my understanding is that teflon tape will be dissolved in gasoline. My understanding is that it may be OK when used in pipe threads where there will be essentially no contact with gasoline, but not OK when exposed to gasoline. A quote from another site: "inside the seal, it should never touch gas, in which case teflon is your best bet becuase it is clean and seals well. but gasoline is made up of 2 perticularly teflon breaking down components, benzene and cycloalkenes. benzene will dissolve the coherent bond of teflon and aluminum, and the alkenes will break down the chemical bond,y ou will be left with a white goo."

So if the teflon tape is going to dissolve, it seems as if a gas resistant o-ring is a better solution. However, I'm not sure I want to try to carve out a groove for an o-ring. What about a stainless clamp to give a bit of a squeeze to the joint?

- My 2006 X5 M54 6spmT with 128K runs fine, zero issues.

- Should I do this "siphon pump" fix on a preventive basis?

I recommend preventative repair of the siphon pump "seals" at about 100,000 miles or more accurately 3000-4000 hours. Or: when the electric pump fails or any excuse to remove the back seat.

Teflon is INERT. I'm not aware of a common chemical that dissolves Teflon.

From the oatey website:

I have to remove my jet pump sender soon and will disassemble the joint I fixed with Teflon tape specifically "FASTape" brand by Oatey. I will report back of course if that was a really bad idea or as predicted perfectly fine idea.

I will also get a sense of the nylon zip tie trick worked to keep the o-ring joint square and functioning.

I actually recommend FIRST check your jet pump "seals" (quotes on purpose as shade on the piss poor design) because I probably replaced a perfectly ok pump with 20,000 miles of life because the jet pump was spraying like a garden hose

Update: I dug into my fuel pump and gauge readings today; the knock off sender unit has a rectangular vs square float and was hitting the back of the tank.

https://uploads.tapatalk-cdn.com/201...88d79b7c96.jpg

I promised I would look at the Teflon seal when I dug into this problem and so I did.

As expected the Teflon which is INERT did not react with the gas at all. I actually un-wound and rewound the same piece I put in five months ago. It looked and felt exactly as it did the day I installed it.

https://uploads.tapatalk-cdn.com/201...e53c18aad6.jpg

The o-ring fix also worked great https://uploads.tapatalk-cdn.com/201...6adf331734.jpg

I will post update for the right side pump and sender unit since I've had to re-enginneer the float that was hitting the back of the tank.

Apparently the OE sender unit has a lower limit of 1.4 L at the flood stage of the surge tank. The knock off was technically more accurate as it will drop down to 0L much closer to the bottom of the tank but was not accurate at the flood stage but was coincidentally closer than the OE BMW part. I tweaked the float arm to get an accurate reading at the flood stage so I will get a hyper accurate DTE (and as a bonus the gauge actually displays the actual fuel level vs "off by a gallon" the factory builds into the design

Thanks for the update on the teflon withstanding gasoline. I guess you can't believe everything you read on the internet! Great to hear the repair is standing up to the test of time.

Like mentioned before, it is likely that the low quality thread seal tape may be plastic and not Teflon.

Do you have the dimension of O-ring and where to get it?