Bigger Rex fuel tank

[pdurham]

Another excellent comment, jadnashuanh: "The US BMW service training sessions say 1.9g. The US website says 1.9g. Until just before actual US release, it said 2.4g, then they changed it. My guess is that if you could get someone to order a larger tank for you, it would probably fit, but who knows what other things may also be involved (could be nothing, could be a different gas line either to the tank or from it to the motor, or a different bracket, or a different filler door, nozzle, or maybe multiple things)."

First, it's news to me that the U.S. website said 2.4 gallons until just before actual U.S. release, when they changed it to 1.9. I had been seeing 2.4 all along as I researched this (part of the reason for all the confusion on the issue) and never caught the change to 1.9. But that would make sense.

Second, you've hit the nail on the head with your comment that while there's likely to be sufficient space for the Euro tank, other things could be different thus preventing us from simply plugging it in. But for that risk, we'd probably be driving our i3 already! We're hoping for more information on whether we can easily install the 9-liter tank in place of the 7-liter tank.

[TomMoloughney]

I think Tom is going to update us on how many litres he is topping up. That should settle it once and fit all.

I let the tank go down to only 5 miles remaining and it accepted 1.75 gallons, so I do believe he 1.9 gallons is the true capacity. I also think there is a good possibility they are using the same gas tank as the European model, with the volume limited by an added internal bladder or some other way (software?).

[MikeS]

May be worth taking the car to a good mechanic and getting him to look inside the tank with the scope they use to inspect engine cylinders.

[pdurham]

Now that's a good question: exactly how do they reduce the capacity from 9 liters to 7 liters for the U.S. models? If we could somehow get an accurate answer to that question, we'd be much closer to figuring out whether we could "repair" a U.S. model. Tom (and thanks for your excellent blog by the way), what's your basis for saying "I also think there is a good possibility they are using the same gas tank as the European model, with the volume limited by an added internal bladder or some other way (software?)"? I agree that it would be easier for BMW to do it without actually producing another tank, but was wondering if you had some specific reason for your suspicion (other than common sense).

[ultraturtle]

... I also think there is a good possibility they are using the same gas tank as the European model, with the volume limited by an added internal bladder or some other way (software?).

The first component I would check would be what appears to be a circular bulkhead plug here:



If I were BMW (knowing that meeting CARB criteria would almost certainly require some adjustments to the tank volume), I would have engineered the tank in such a fashion that it would be as easy to do as replacing a flat bulkhead plug with one that intrudes into the tank to reduce volume.

[mindmachine]

... I also think there is a good possibility they are using the same gas tank as the European model, with the volume limited by an added internal bladder or some other way (software?).

The first component I would check would be what appears to be a circular bulkhead plug here:



If I were BMW (knowing that meeting CARB criteria would almost certainly require some adjustments to the tank volume), I would have engineered the tank in such a fashion that it would be as easy to do as replacing a flat bulkhead plug with one that intrudes into the tank to reduce volume.

The computer system would however also need to know that the tank is smaller in order to project the range of the Rex and display it on the instrument panel.

[pdurham]

Excellent information Tom; I'm impressed. Where did you get that excellent picture? Perhaps I could find some more information on the bulkhead plug and whether it's a separate part there?

Is there a way to find out if what you refer to as the "circular bulkhead plug" is a separate part and whether it can be removed and replaced by the Euro version? Perhaps my friend, who is planning on visiting a Belgian BMW dealer today to check on the availability of the Euro tank as a purchasable part, should be checking on the bulkhead plug as well. Perhaps I should have my friend buy the bulkhead plug, if possible (and it looks like it would be much smaller and cheaper than the whole tank), to bring home and compare to the U.S. version of that part. (I just realized that given the time difference, he should have already gone to the dealer. But no word from him yet, so maybe that errand has been postponed.)

As to the computer needing to know the capacity of the tank in order to accurately project the range, that's a valid point as well. But, though I don't know the first thing about all this of course, I doubt that would stop the car from moving. In other words, if the computer incorrectly indicated the range but you knew you had about 1/2 gallon more fuel than the computer thought you did, you'd know that you had an extra 20 miles or so of range beyond what it was projecting. Also, I would imagine the computer has some way of measuring how much fuel remains in the tank (with the result that although it may underestimate the range of a full but "modified" tank, it would provide an increasingly accurate remaining range figure as the tank emptied). All just guesswork on my part.

[BrianStanier]

I would suppose its the fuel gauge?

[ultraturtle]

Perhaps I could find some more information on the bulkhead plug and whether it's a separate part there?

First off, the existence of such a plug is pure conjecture on my part. Just a guess.

Parts can be found at http://www.etk.cc/bmw/EN/search/selectC ... 3+Rex/USA/.

Specifically, the fuel tank can be found at http://www.etk.cc/bmw/EN/search/selectC ... 6/16_0921/.

[Gonville]

Also here....previously both models had same part number. Not rechecked that but as Tom says some other modification perhaps.

http://www.realoem.com/bmw/partgrp.do?m ... spid=56091