There are occasions where the BMW cooling system fails rather suddenly (V-8
E39's seem more prone than most), typically a crack in the plastic hose
connection on the radiator. The buffered system is fine and you're correct
that it indicates "nominal" temperature across an acceptable operating range
of temps by indicating a 12 o'clock needle position.
An old style temp gauge will rise and fall slightly between the thermostat
setting and its max load temp (think steep hill, high rpm, hot day). It
will also show a steady rise if coolant is rapidly leaving the system
through a leak, an early indicator that you might want to prepare for a
rapid exit and shutdown.
The buffered gauge will do neither. After a sufficient amount of coolant
has left you'll be confronted by a rapidly rising gauge and precious little
time to perform neccessary action.
While there appears to be no way to modify the gauge, aftermarket systems
work well and can also report oil temp (a luxury afforded M-drivers vice the
worthless MPG gauge), oil pressure, volts, or whatever. These are minor
mods, the kits are typically well-engineered and will not harm the vehicle.
R / John
Now, this may not be relevant to modern gauges and cars, but a trick I
learned years ago on race cars that you can drive to the track (ahem)
is to use the same electrical temperature gauge for both coolant and
engine oil temperatures. Obviously, you need to have both sensors
present. The trick is just a simple toggle switch to change between
them. The temperature ranges are similar.
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