Just put coolant in it a day and a half ago to the Max line and today I drove around alot and now all my coolant in the resavor is gone, and it's making a hissing noise, any idea why it's doing this?
Several things. The hissing is the pressure that's built up in the cooling system being pushed out when it reaches the caps limit and go's to the reservoir. You have a leak some where, could be hoses could be headgasket, heatercore, radiator. Few different places.
#1. Check for leaks (Radiator, hoses, Intake Manifold coolant lines, etc...)
#2. Check your radiator to see if there was sufficient coolant in there. (it might have pulled it in)
#3. Blown head gasket
DONT DRIVE IT UNTIL YOU FIGURE IT OUT! OR IT WILL BE MORE EXPENSIVE TO FIX.
