Not likely. The engines that were used in the 98 Malibu (the 3.1 L v6 and 2.2L 4cyl) were both known to have head gasket issues. Usually on these engis, the head gaskets break down between the coolant and oil channels. That means that the engine could easily still have full compression on all cylinders, which would cause no difference in power. Have it checked by a professional before you damage the rest of the engine.