If you have problems with your Vectra C 1.9 CDTi running cold in the winter and other times then you may have a thermostat issue.
There are two orginal thermostats fitted which both look the same, 55487784 and 55187784.
Both these part numbers have been superseeded with 55203388
The new part will allow your engine to warm up and stay roughly at 80-85 degrees and finally you will get really hot air from your heater which I never had from when I first got the car.
Finally do not follow the Haynes guide. There is no need to drain your system unless you want to reuse the coolant (it will take approx 2.5 litres to refill done my way) or remove the battery cover and battery. Make sure you do this when the engine is cold!
The Thermostat is supplied as a complete unit with its housing and Temperture Sender (it should cost around £40 plus antifreeze and a small Jubilee Clip from the dealer).
You can find the housing on the right hand side of the Engine block nearly opposite the glow plug relay which is at the side of the battery compartment (looking at the engine bay from the front of the car).
You will need to move the Glow plug relay to one side to make things a bit easier. Then remove the intercooler pipe and all the pipes connected to the Thermostat housing including the wiring to the Temperature sender. It is held in by 2 x 13mm bolts.
There is also a nut which is holding a couple of pipes to the housing which also needs to be removed and the pipes pushed out of the way so you can get the thermostat housing out. Under no circumstances drop any of the bolts or nut otherwise you will have to get under the car and drop the flap on the plastic undertray/sump guard which is not easy when you are working on the drive .
Clean the area around the engine block with a scouring pad before refitting the new housing. The rubber gasket is built into the new housing so there is no need to use any sealant. I think you need to torque the bolts done to 20Nm but I need to check.
The above info has been put together will information gained from other members on the forum plus I had the same issue and this what I did to resolve it.
Please beware that many Vauxhall Dealers will claim that there is no issue whatsoever and are totally unaware of the new part.
Before this was done my car on a really cold day would not warm up unless I was stuck in traffic. The Temperature Gauge would hardly move for most of my journey now it gets to 80-85 degrees and stays put.
Mods can this be made a sticky as the question regarding 1.9CDTi's running cold is always being asked on the forum.