it is in the same place as a corsa c

If its anything like on the corsa C, the drain plug is at the bottom of the rad on the drivers side pointing into the engine bay. You'll need a flat head screwdriver to undo it.

And the warming the car up with new coolant is best done with the cap off the expansion tank so any air trapped in the system can escape 'cus it can't pressurise.

[Edited on 01-10-2010 by neil h]

On my Mk4 Astra.

Apparently there is a drain plug on the drivers side of the radiator, havent looked for it yet. Obviously car cold, undo coolant tank, undo plug, catch the stuff that comes out (dispose of it where??? :o) put the plug back in. Ive read then to fill the radiator back up and idle the car till it warms up (will probably take a day at this temperature for my diesel to warm up on idle :boggle: ), put the heater on full and the repeat the above once its cooled down again? Is this really required? Surely gravity will pull all coolant into the radiator as it drains, job done, refill?

If anyone knows the type of drain plug on the mk4 Astra that would be most helpful :)