Fluid temperature regulator includes a unitarily-formed housing having an inlet, outlet, bypass outlet, and plurality of valve chamber openings, in line with respective valve chambers. Valve holders are removably disposed within valve chamber openings to position thermostatic valves within the valve chambers. Each valve holder includes at least one wall having at least one holder outlet opening and holder bypass outlet opening. First and second regulator flowpaths through the regulator are defined through the regulator inlet to either the regulator bypass outlet or regulator outlet depending upon whether the thermostatic valves are disposed in a first or second configuration, respectively.