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The tried-and-true swap to a lower temperature thermostat is nothing new. If  you've made upgrades to your engine, and are looking for better performance, a  drop in temperature will always be a benefit - especially if you are a racer. I  felt a 160° thermostat was a bit on the low side, but 170° is perfect, especially  if you are replacing an original thermostat rated at 180°. It’s also feasible to  simply use a 180° version in place of one that is rated higher, especially if you  feel that 170° is even too low.    While there are some options out there to buy current "alternative  temperature" thermostats, I made went to Stant right from the start (Stant, by  the way, is the OEM supplier to Ford). Thus, these are all OEM-quality  thermostats using actual 170° "heat motors", not just generic versions using  lighter springs. They are also a perfect fit, so you’ll have no worries about  improper coolant flow. Since there is no middle-man to go through, the savings  are passed on to you! Even better, a portion of the proceeds go to St. Jude  Children's Hospital. Here is a look at a 170° thermostat in  action, compared to a factory Mustang  180° version. Mine (on the left side in  each) begins opening just as it passes  170°, and is fully open by 190° - while the  factory thermostat is catching up. If you want to drop your engine  temperatures 10-20°+, you aren't going to go wrong here!   Once you install a new thermostat, there are two considerations that come in  to play in order to take advantage of it. First, a proper coolant mixture is  important. See the Motorcraft Coolant chart for mixtures based on your  climate, which is also available any time through the tab at the left.  Additionally, your fan settings need to be changed through a tune or with a  hand-held tuner. Otherwise, you will only benefit when the vehicle is moving  and air is flowing through the radiator.  This is a good starting point, using an SCT tuner and my own 2003  Cobra as an example (the Cobra has unusually high factory fan  settings already). The low-speed fan turns on at 186° now, and the  high-speed at 190° if necessary. The low-speed fan here will shut  off around 176°, with the temperature drop shown on the  Aeroforce Interceptor mounted on my steering column. All have  been used in a wide range of vehicles, and they absolutely work!  As always, performance modifications to your vehicle are undertaken at your  own risk! Although a thermostat swap is straight-forward and non-complicated,  you are ultimately responsible for the work as well as the outcome. Please use  factory service manuals and follow their procedures accordingly. 
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