In terms of the guage, my concern, beyond admittedly obsessive
> curiosity about engine performance parameters, is that I don't want a
> sudden extreme overheating situation which I, presumably, could have
> detected earlier on with a linear guage reading.
I'm not sure you could. Each car has an upper and lower limit it may run at under normal conditions. So if you were used to observing those how would you tell it was suddenly overheating - anymore than the BMW gauge rising as it will?