I think my radiator has very slowly over 3 months leaked out all of the coolant - I just took a pic of the little plastic resovoir thing under the hood (left) and she's empty.

She's been running warm lately, however not overheating (I guess she's tough?) but I think I need to put in coolant.

Do I dilute the coolant? I know I need the green stuff, should I also mix it half half with distilled water or all coolant? Can I buy $20 stuff at bunnings or do I need $80 stuff?

I'll only do this once, if it keeps occurring I'll take her to the fixer.
(He only just looked at it 2 months back and I even mentioned occassional odd heating, he checked pressure on radiator and said she's golden - so I'm lost. I trust the fella too, he does a lot of old fords)