It looks as if the assembly is being compressed (and bent) when you screw it down, rather than the sprung section taking up the height difference...?

I am assuming that the bottom of the tank is getting sucked up(and top down) further than the sprung travel ??

That's a reasonable theory but the tank walls are very thick - I'd be surprised if it can deform that much under vacuum alone.

Maybe it's had massive hit from underneath at some point and is permanently deformed. :dunno:

Or the sprung section is binding and not allowing enough travel. :dunno:

The compression under vaccum is my theory because putting the assembly in is not difficult and it slips right in without the gasket, when I add the gasket, it doesn't slip as easily but that's normal.


I don't think its been hit, the car has only been on road for the last 6 months (went light off roading prior to that) and the first broken assembly was 10 months old when it broke suddenly. and the second one was 10 days old.



I'm guessing if the tank was permanently deformed, it would have broken sooner.



The only two options I see would be high preassure not being vented and the tank expanding a little more than the full course of the assembly, allowing it to move and get out of its locating hole or the tank being vaccumed into submission to the point where it breaks the assembly.



I'll need to take it out again and take some measurements to see how much course there actually is. As for the strengh of the tank, it is strong but I can make the top move a little without too much force so I'm guessing the V8 vaccum pump would be able to do better.

It looks like when you dry run (no seal) you are hitting the bullseye with the post and socket but when you redowith the seal the post is missing the target and causing the stress.

You have to put the seal on the sender unit first not on the tank. Wet the seal to help it going in smoothly

Save extremely harsh external damage (drive over a rock) virtually no chance the problem had anything to do with change of size of the tank

I'm going to change it again as soon as I reach a bmw dealer to sell it to me and hope you're right... For my peace of mind, I'm going to check the vent valve since I don't understand why it broke the first time after such a long time without issues...


I'll see if from the pump side I can check its correctly seated when I mount it.

Engine vacuum (atmospheric pressure) could easily crush tank. Also fuel pump could easily crush tank the same way if tank is not venting.

e53 Fuel Supply Detailed (fuel pump / siphon pump diagnostic help)
 

That's true 15psi is substantial force.

You can try to take off the gas cap while the engine is running you’ll know right away.

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The pictures are of the jet pump or left side sender. Same as Port side. Driver side in the USA (LHD). I thought I read right side above.

Hi again,


I changed my fuel sender (driver side, left side of the car, LHD car) and made really sure it was correctly in place. I used the moving it method, i lowered it vers slowly an once it sat, I raised it by a centimeter and tried moving the bottom to make sure it was in the recess (blocked on all sides) and not free in some direction.


I also took some measurements :

From the bottom point to the metal ring surface on the tank,

the tank has 33.5cm depth.
The fuel sender is 36.5cm just sitting on the bench
the spring part is 6cm.


That would mean that when sitting in the fuel tank, its compressed by 3cm.



Once fitted, I was low on fuel so I went to fill up and had a little drive ahead of me. The fuel sender gave values for 70km before it went back to 0.0L....
I was on the highway, driving between 110km/h an 130km/h (3000rpm), light driving on a warm day with no urgency.



I'm fed up, BMW dealers were on holiday so its still in the tank. Its been 10 days since it broke. My plan is to take out the fuel pump side and use my phone to take a picture (or 20) of how the fuel sender is sitting in the tank. I have to understand and I would enjoy not to spend another 100€ on a sender for half an hour of use...


It might take a while, my timing guides died yesterday morning so I'll have to fix those before I throw more money at the fuel level...