There is a check valve inside the o-ring connection or the extra unlisted and no seal connection but it's not to hold pressure (no seal) it's just to keep some fuel in the siphon jet lines so they don't have to prime each time the car is used.

There are two connections at the top of the siphon jet intake (where the return line from the FPR is attached). I forget which is above and which is below but I think the check valve is inside the one designed to come apart (with o-ring and design defect)

The defect in the o-ring design is that it's only held together from one side and not from both sides. With 15psi and over an inch of area means 20 pounds of force approximately an inch offset or 20 inch pounds of torque for thousands of hours. It will twist enough eventually that the o-ring will squeeze out of its groove and has will spray out like a garden hose.

I would premptive strike on ANY BMW with this design defect at about 100,000 miles to beat it to self destruct.

It only takes a couple zip ties or a single screw to permanently fix the problem rather than wait until it strands you with 75 miles distance to empty (TWICE in one week for me thanks to the hundreds of erroneous web pages completely void of accurate info on how the BMW X5 fuel system works)

First time was at 6°F on my way to cat sit for a client and the second time was 25° at 11pm with my 74 yr old dad with me. Very uncool (figuratively) both times. Was enough to piss me off enough to actually solve exactly the why to educate myself to avoid repitittion and actually solve the actual problem at hand.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)