e46 330 petrol sport engine temp

[gazsharp]

The temp gauge falls to just above a quarter when driving and then returns to half whilst stationary. Any ideas why this would happen.

BMW dealer said not to worry, but think something not right

[t-bagger]

Probably the thermostat, they are 'MAP' controlled on the M54 engine by the DME so can do some slightly odd things when they fail.
Not a massive headache to change, just make sure you fill and bleed the cooling system properly.

[blackspider]

As T-bagger said its likely to be the therostat-they used to be as common as muck.
What will have happened is the plastic lugs that hold the stat together will have snaped off causing the stst to fail in an open position-the later stats have metal supports in the plastic lugs.
Easy enough to replace