Replaced my thermostat today based on the very useful 'How to' on this forum. I did not remove the header tank, I syphoned it dry.
Problems encountered and solutions (posting just in case what I type may be of some help to someone else): -
1) had to prize the EGR cooler bracket off with a tyre lever. the bracket bent a little but was easily straightened with mole grips.
2) I dropped one of the M8 * 25mm length bolts when installing the new thermostat. Curses as it is now lying somewhere on the undertray. Cannot see where. Luckily, I live a 5 minute walk from Halfords, so I got the last two which they had in stock. Curses over as this allowed me to complete the job.
3) So as not to lose any more bolts, I then used blue tack on the bolt heads to hold it into the hex socket. This gave enough hold to reduce the risk of the bolt falling out before it engaged into the engine thread. This worked a treat.
3) When installing the new thermostat, you are effectively working blind to line up the holes of the thermostat to the holes in the engine. I therefore got a piece of thin piano wire out of the shed and proded this through the thermostat hole. My theory was that if you did not have the two holes aligned, the piano wire would not be able to be pushed any deeper but if they were aligned, the piona wire would be able to be pushed in (up to 25 mm) further. I did this and when the piona wire went fully home, I simply held the thermostat carefully in that position with one hand, with the other hand, I removed the piano wire and replaced this with the pucka bolt. This worked a treat and in no time, I had the two bolts installed.
Results: - Normal temp now sitting constant at 85 C and heater giving heat that I have missed for the last 2 years.