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Old 10-03-2021, 11:52 AM
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andrewwynn andrewwynn is offline
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Quote:
Originally Posted by X5chemist View Post
I don't let it go under 1/2 tank either. I didn't have time to fill it last week. It went 325+ miles on 3/4 of a tank so I'm happy.
There is no good reason to avoid going below half tank and you risk getting stranded if you don't occasionally make sure the tank can go below 1/4 to make sure the siphon jet is functional.

Explain your rationale behind 1/2 tank.

I wrote "the book" on e53 fuel delivery, so I know the fact based answers.

The way the X5 fuel tank works, once there is less than 27L of fuel, it relies on the siphon pump to draw fuel from the left side of the tank.

The right side has a sump where the pump is, that holds approximately 5L of fuel so effectively the truck only sees 5L fuel tank no more once 3/8 of a tank or so.

This is not a "problem to be avoided". It's a normal operation that needs to be occasionally tested.

When the siphon jet fails (and it almost certainly will) it's an easy repair with an o-ring and zip tie. (the failure can be prevented with a zip tie if done preemptively).

All BMW should go through the test of the siphon jet at least 1-2x per year until the repair is done.

I learned the hard way since my wife never went below 3/8 tank so I got stranded on a freeway 50 mi. from home on 6 F=-14 c day where all the tow trucks were busy helping people with dead batteries.

The only benefit of keeping half tank minimum is having more immediate range without stopping for gas.

I drive until my low fuel light comes on virtually always. On 3.0 engine that's with 8=11.6L of fuel, with 4.4, 10=13.6L of fuel.

11.6L, just over 3gal means over 40 miles range on a bad day, and I'm never farther than that from a gas station.

So, once you confirm you can drive down to single digits distance to empty, feel free to waste half your range filling up twice as often if you feel you need to for some reason, but do the test occasionally or you will certainly get stranded "that one time" you need more range.

Also, as I started, explain the reason for half tank, so if there is a good reason I can update my "book on fuel supply".
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