Its actually water that cools your engine. Always fill in coolant diluted atleast 1:1
I once made the mistake of filling in fully concentrated coolant, oh boy! I ended up two days later wondering why my ac stopped working on an open road. Ten minutes later i saw the temp. needle and i was astonished man! The needle was at 75%. MY thermostat valve was stuck. Well, i got it replaced and then filled in caltex coolant diluted 1:1.
Anyways, i learnt it the hard way. I'd never reccomend this to anyone,