Wait until the engine is totally cold. Look under the car at the radiator, there should be a drain petcock that you can open easily to drain some of the coolant from the radiator. You will only have to drain about two to three quarts of coolant to get it where you need to. Then remove the thermostat housing. Clean the gasket surface and replace the gasket. (If the thermostat hasn't been replaced recently, change it too.) Put the housing back in place tighten, not too tight because overtightening will cause it to break. Refill the radiator and start the car. Allow the car to reach operating temperature and refill the radiator completely. If the leak stops problem solved, if not then the intake gasket will probably be the next place to look. You may also want to use a torque wrench to check the intake manifold bolts to insure they are properly tightened before you change the intake manifold gasket. Sometimes these bolts work loose and just need to be retightened.