The Heater in my 2007 Pontiac Grand Prix GT wasn't heating the car. After checking with my mechanic, he told me to save alot of money and fix the heater myself by flushing out the heater with water, which worked. Unfortunately, when I went to re-install the two hoses, one of the bolts that attaches the hose to the engine itself snapped. My question is: Is the liquid that runs through the cabin heater under pressure? I have to have the bolt replaced, but is it safe to drive the car?