RE><E36> Another Person with Fuel Gauge Problem

["Chao, Harvey" <harvey.chao@xxxxxxxx>]

On the assumption that the design of the sending unit  used by BMW is
essentially standard across years, and models, the problem you are having
could be a small amount of grit in the sending unit.

The design of the sending unit in E28 cars is a vertical, hollow, oval cross
sectioned, thin wall aluminum tube.  Inside the tube, matching it's cross
section, is a float that travels vertically with the level of gasoline that
is allowed into the tube via small hole(s) near the bottom.  The clearance
between the float outside dimensions and the inside dimensions of the tube
is very small, perhaps a millimeter max.

I had the same problem with my car and eventually replaced the sending unit
with one from a salvage yard.  I then took the original unit apart.  What I
found was some fine grit that was inside the unit and was causing the float
to bind against the tube walls.  The grit probably got into the tank with
some bad gas at some time or other.

Should you desire to attempt to disassemble your sending unit, I would
caution you that the way it is constructed it is highly unlikely that you
will succeed to disassemble it without destroying the very fine resistance
wires that run up and down the interior of the tube and which are riveted to
the top and bottom.  Since the top or bottom has to come off to gain access
to the float  . . . . .  Trying to flush out the assembly without taking it
apart would be difficult for the following reasons:  1) close tolerances
between the float and tube walls, 2) small holes allowing gas to get into
(or out of) the tube, and 3) you are messing around with a bunch of gasoline
that could make life extremely "exciting" in a real hurry if it ignited!

Harvey

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