I just changed the thermostat and thermostat housing in my Cooper (2004, non-S). That all when fairly smooth (I am not a mechanic by any means); however, this is only the second time I've had to replace the coolant and, for me, it takes a long time (read as "days") to do. Mostly, it's because the damn Bentley manual (which I own) confuses the crap out of me when it comes to this procedure. The book tells you to do step A, B, C, and so-on without any mention of turning the car on during the process. Then, there is a "Tip" at the end where they tell you to turn the car on (heater on HI, fan on low) and fill slowly. I have done exactly what the manual says, but it always takes days to get to the point where the coolant level in the expansion tank stays between Min and Max without being fully drained each morning. There are no leaks, either.

How long does it take you guys to refill your coolant after a change and how do you do it? Also, is it safe to replace that PITA spring clamp on the radiator hose (the one used to drain the coolant) with a worm gear type? I hate that thing...

 

I don't have the Bentley - does it mention opening the bleed valves? A non-S has 2 I believe.

Anytime I encounter one of those PIA clamps I replace it with a screw type if pressure exisits and even have used 'zip-ties' in other cases like the air box (aka cable ties)

 

Yeah. The manual says to loosen it and then pour coolant into the filler neck and close the valve once coolant starts to leak out of it.