Originally Posted by Mustard3
I change both thermostats and now once warmed up does not drop below 86 deg. Could you have a faulty main thermostat, even though it's new?
I dunno really.
Noticed mpg dropped down from a consistent 40mpg to around 34......looked into possible causes - low operating temperature, which tied in with me having to set the climate control to 23 deg to get the cabin warm in the morning.
Looked at hidden menu and sure enough was rising slowly to 50 degrees on an 18 mile journey which is mostly motorway at a steady 60mph. Reverse journey achieved 60 degrees ( probably due to ambient air being warmer at 4pm as opposed to 6am).
Replaced EGR thermostat - immediately the cabin felt warmer, and temp shot up to 75, staying around that on return journey too - sometime getting to 77. Read the DIY for the main thermostat and the symptoms described exactly what I had which resulted in main thermostat being changed on the 330d.
So I changed it - and sure enough after a few runs around locally it eventually got up to about 89 degrees - once. I was on holiday over xmas so didnt do much motorway driving. When i eventually got on motorway it seems to cool down - suggesting main thermostat is open at about 55 degrees (temperature flies up to 50 in 5 minutes, but then fluctuates up and down around 60). As i said previously it can sometimes get up to 70 but does struggle, then one day recently it climbed to 96(regen?), but not since.
Doing my head in
will look at the top hose mod