If your mechanic only changed out your radiator & sensor and did not bleed it thoroughly, it can lead to overheating later. Or, if you're still on your original waterpump... it's probably failing.
Or, if you may have another leak occurring else where that can allow air to be drawn into the system.. which would lead to your "random" overheating also.
You try and bleed your cooling system properly, usually takes 30 minutes or more (if it's your frist time) - search : DIY cooling system bleed
And, never over fill your expansion tank. Fill only to between the two bubble mark on the measure stick.
Last edited by BimmersGarage; 11-29-2012 at 12:34 PM.