on 15/02/2019, Dave Plowman (News) supposed :
Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.

Mine does that, it is absolutely useless.. It shoots to dead centre as
it warms up and just stays there giving no clues until it has over
heated - entirely pointless.

A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

Mine can be accesses via OBD, or via dash diagnostics - a sequence of
button presses on the odometer reset button.