My main involvement with the car scene has been with the '03-'04 Cobra "Terminator" crowd that has gone back many years, including my own web site dedicated to the vehicle and its history: www.terminator-cobra.com. One of my side projects, that is on hold now due to the insanity of 2020, has been custom Stant 170° thermostats (Stant is the OE supplier, by the way). You can buy them on-line for something like $70, but since I decided to take a break - and may not ever get back to it - I decided to share the "secret" of them for anyone that has just basic mechanical skills and wants to save some coin.
For about $20, this is a total DIY project for the ST that takes about 5 minutes and is laughably simple. Since the factory RT1225 thermostat is a 180° version, many might want a lower-temp 170° after getting tuned and modified. All you need to do is buy a Stant 14138 (180°) and 14147 (170°), make a quick part swap, then add a gasket to its flange and you are done. The gasket is also easy to acquire as a Stant 25282 (the same as NAPA 1093 or FelPro 35710), which is needed here so the flange is the correct diameter for the housing.
Here is the 14138 (both MUST be from Stant, easily identified by the blue & yellow box!):
With this in hand, you just need to pull out the brass 'foot' and its internal spring. The spring sits inside with a larger coil on the bottom, and then will be transferred to the other thermostat. You can then toss the main thermostat body. Here's what you have once the 'foot' is removed:
The Stant 14147 looks like this, which is the 170° base that has a 56mm OD flange compared to the 54mm flange of the 180°:
You simply then snap the brass foot and spring back in the bottom of the 14147, then add the gasket to the flange which brings the diameter up to 61mm for a proper fit in the housing (this thermostat also fits the Ford Coyote 5.0 V-8):
In the above image, which is then the final product, note the orientation of the gasket since it has a flat side that faces down. The internal groove will fit right over the flange of the 56mm 14147 housing and you are good to go. As an FYI, here is the OE Motorcraft (also made by Stant) RT1225 180° thermostat. It looks a bit different, but the dimensions are the same as above:
For about $20, this is a total DIY project for the ST that takes about 5 minutes and is laughably simple. Since the factory RT1225 thermostat is a 180° version, many might want a lower-temp 170° after getting tuned and modified. All you need to do is buy a Stant 14138 (180°) and 14147 (170°), make a quick part swap, then add a gasket to its flange and you are done. The gasket is also easy to acquire as a Stant 25282 (the same as NAPA 1093 or FelPro 35710), which is needed here so the flange is the correct diameter for the housing.
Here is the 14138 (both MUST be from Stant, easily identified by the blue & yellow box!):
With this in hand, you just need to pull out the brass 'foot' and its internal spring. The spring sits inside with a larger coil on the bottom, and then will be transferred to the other thermostat. You can then toss the main thermostat body. Here's what you have once the 'foot' is removed:
The Stant 14147 looks like this, which is the 170° base that has a 56mm OD flange compared to the 54mm flange of the 180°:
You simply then snap the brass foot and spring back in the bottom of the 14147, then add the gasket to the flange which brings the diameter up to 61mm for a proper fit in the housing (this thermostat also fits the Ford Coyote 5.0 V-8):
In the above image, which is then the final product, note the orientation of the gasket since it has a flat side that faces down. The internal groove will fit right over the flange of the 56mm 14147 housing and you are good to go. As an FYI, here is the OE Motorcraft (also made by Stant) RT1225 180° thermostat. It looks a bit different, but the dimensions are the same as above:
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