Mark,
Normally you have to take off cambelt to change thermostat on the Astra 1.6 8v models. I did with my 2000 Astra 1.6 8v 2 years ago, now A OK.
It's your lucky day, this is a cheap thermo bypass change. Now available on Ebay, see item number :- 160330800689. You could change this yourself, follow instructions. Make sure your engine is cold first before attempting change.
If I had realised this 2 years ago, I would have just used this replacement thermo instead. Would have saved on time & cash.
The prob with your old one is that it will be stuck in the open position, taking ages for you temp gauge to get up to normal running temp.
Once new thermo replaced, your temp gauge will be up to normal running temp (half way on gauge), within 2/3 miles of driving.
A useful Vauxhall forum for you:- http://www.vauxhallownersnetwork.co.uk/forumdisplay.php?f=83
George (Astra owner)., May 2009
