http://clubjazz.org/forum/index.php?topic=6965.msg31098#msg31098system holds just less than 5 litres, buy a 5 litre 50% premixed OAT or HOAT silicate free coolant from Halfords or wherever at about £20 (I have used Halfords in my cars and motorbikes no problem) .
when you use the premixed you know it is 50% and is mixed using distilled water - both important points. When the % of antifreeze (ethylene glycol) goes below or ABOVE 50% the freezing point of mixture is raised, so 50% gives best protection. The ethylene glycol antifreeze does not wear out, it is the anti-corrosion chemicals (OAT - organic acid technology) that get used up as the coolant ages so although the radiator wont freeze, the coolant system will corrode,
As far as changing coolant goes I learned my lesson years ago when I went to town and drained the system dry, flushed it and poured new coolant in, it took weeks and a few red liners on temperature gauge to get system and heater working properly again, now I do a shortcut method which is a lot less hassle - see below
when I did my last Jazz I just undid the radiator cap and the drain screw on bottom of radiator, drained what wanted to come out into a plastic bowl and when it had stopped flowing measured what came out with my wifes kitchen measuring jug, made sure same went back in that came out (about 2 to 2.5 litres from memory). Drove the car as normal for a week and did the same again with remaining coolant, reckoned I had changed about 70% of coolant this way but didn't have any problems with airlocks and stuff.
