Coolant

[nakadian]

Hey guys!! It's been a while posting here and Im even a little nervous! haha
Anyway, to the point! I sold my TI (i know ;(( ), it had been hit from underneath on the rear passenger wheel and it had been "fixed" but just not fixable as a whole... I had bought a BMW Z3 now with the same 1.9L engine! 2 days into it, guess what happens! The plastic part described in the 1st post in the Maintenance section of the forum breaks and coolant on the ground. Smoke also took part in the experience. However, it didnt go in the red section and we were able to drive the car home, still not sure what the problem is, and just drove slowly, shutting the car off and on and putting water. The ride was about 5 miles or so... The car never went to the red section !! Changed the plastic part and put water mixed with coolant. Driving 2 days, the car was fine. Then it overheated again a little with the A/C on max. The 1st time the A/c was also on... The guy that sold me the car swears he didnt have problems and he seems like a cool guy and that im just so unlucky... He recommends to use only coolant, no water, check all hoses, and double check if theres airbubbles in the cooling system... It really doesnt seem like a headgasket because there is no water coming out of the exhaust and it doesnt overheat right away. My dad thinks the level of the water went down a little but not completely sure.
What is the right cooling system for the M44 ?? Anything would help!
Thank you guys!!!