It is. I always thought it would be easier if the relief was in the manifold. I always put a few small dabs of gasket sealer in the relief of the housing and then put the thermostat in the housing and give the sealant a few minutes to set up. Then install the gasket and place the housing on the manifold. The few dabs of sealant keep the thermostat from slipping and getting stuck in between the manifold and housing outside of the relief which could go unnoticed.