Roller cone drill bits may be provided with pressure relief mechanisms operable to control lubricant pressure within respective lubricant systems. Each lubricant system may be enclosed and isolated from downhole well fluids. Portions of each pressure relief mechanism may be completely surrounded by lubricant to increase downhole life of associated operating mechanisms and to produced more repeatable and more reliable opening and closing of the pressure relief mechanism. The downhole drilling life of bearing surfaces, fluid seals and other supporting structures associated with roller cones mounted on support arms of such roller cone drill bits may be substantially increased. Each pressure relief mechanism may be locked in a closed position to assist with filling the respective lubricant system with lubricant.