FORD-G5 thermostats only for Shelby GT500 5.4 or 5.8 engines. They are custom made with the same size diaphragm and bypass control as the OEM units. Each of our thermostats is modified by hand using only U.S. made parts and then quality inspected to ensure consistent opening temps. These t-stats are the only ones specifically designed to fit these applications making them the best performing low temp units on the market! Whether you are using an aftermarket radiator or not, our thermostats will provide the best possible heat dissipation from your setup along with a faster warm up time than a 160° unit or a thermostat with holes drilled in the diaphragm. We believe the 170° opening temp is the ideal balance for high performance engines, providing high flow to your radiator by mid-180 temps while still providing good all season performance. With proper fan settings your coolant temps in cool weather will be in the 170s and in hot weather the 180s, giving those running high levels of timing and/or boost added protection against engine-damaging detonation as well as maximum power output.