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How do I determine what temperature thermostat would be best for my 69 Mach 1 351 w with A/C?
Thanks!
 

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just get the most popular one. I have a 69 with a 351 and use what i think is a 180 degree mr gasket thermostat. I have a good radiator, good fan but it still runs a little hot so i'll get an oil cooler as well. Problem with the bigger fan is now there's no space for a shroud. The old V8s are notorious for a reason. No matter what you get at some point you'll find yourself chilling on the side of the road while shes cooling down but its all part of the fun! right?...
 

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195 degree. Just make sure it's a good one like a super stant or if you prefer one of the high flow Robert Shaw ones. Even at that, I'd still drop it in a pan of water on the stove with a thermometer to make sure that it opens when it should.
 

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The engineers at Ford Motor Company claim we should be using 192-195 degree thermostats. And so does every single other person I've judged reasonably qualified to offer an opinion, so that's what I use.
My personal experience with thermostats from the parts stores has been bad enough that now I will make a special trip (if necessary) to the Ford dealership to get a Motorcraft branded one. Not that they are perfect but odds are very good that I won't have to be replacing it a couple of months later. Other folks don't seem to have issues using just whatever random ones but I'm not the only forum member to experience the opposite.
I see Mr.Gasket mentioned. Could be just me, but I have sworn I will never again buy anything with their name on it. I've had some very bad luck with their products over the years and I really hate doing repair jobs over again.
 

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I tried the MrGasket thermostat.
Failed, stuck closed after 10 days of use.

Most will say to use a 195 thermostat. I prefer the 180.
160 would be too low.
 

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I recently switched from a 195 degree to a 180 degree. Seems to be running much cooler than before. But if I'm stuck in traffic amd barely moving along, then my needle starts to creep up and that's when I start getting a little nervous. But for the most part she running right where I like it to with the 180.
 

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I recently switched from a 195 degree to a 180 degree. Seems to be running much cooler than before. But if I'm stuck in traffic amd barely moving along, then my needle starts to creep up and that's when I start getting a little nervous. But for the most part she running right where I like it to with the 180.
How do you know it's running cooler? Do you have a quality temp gauge that has a graduated scale?
 

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Another vote for getting the "most popular" one. It's popular for a reason ;)
 

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I recently switched from a 195 degree to a 180 degree. Seems to be running much cooler than before. But if I'm stuck in traffic amd barely moving along, then my needle starts to creep up and that's when I start getting a little nervous. But for the most part she running right where I like it to with the 180.

Well, it will run cooler during normal operating/driving conditions, since the thermostat opens at 180 instead of 195. But it will not help you with overheating in traffic. Above let's say 205+ both are fully open and temperature depends on your cooling system.

Keeping the temperature constantly (too) low is not a good thing for your engine. Engines are designed for a certain operation temperature, this is why they have a thermostat.
 

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Lots of people seem to get scared out of their wits that their motors are going to blow up if coolant temperature goes over 200*F. Well, unless somebody messed up the installation, it won't. A temperature of 200-212*F is "Normal Operating Temperature" for the SBF. Below that coolant temperature the oil will not get hot enough to properly lubricate and purge itself of contaminants. Even temps of 220-230*F for extended periods, like climbing a long, long grade are okay... it's when coolant temps exceed 240*F that you can start experiencing localized steam pockets as the coolant around the top of the cylinder and combustion chamber starts to boil... from there things start to go downhill so it's time to pull over to the side of the road and run the engine at fast idle until the temps start to go down. This is, of course, not the procedure if something is wrong, like a broken fan belt, bad water pump, coolant loss or issue other than an extended heavy load has caused the heating.
 

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Another vote for getting the "most popular" one. It's popular for a reason ;)
The reason that particular part is popular is because people don't fully understand the concepts behind a pressurized automotive cooling system. An example would be the previous poster saying he had a 180* and thought it ran cool but had an issue when idling. The posts by @Woodchuck, @Mustang4SF and @GypsyR explain the engineering without using the math.
 

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180 fail-safe. If it fails, it’ll fail open Figure out how to make a shroud work; they work very well.
 

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To answer your question, there is a table in the Specs section at the end of one of the chapters (either the Engine or the Cooling chapters) of the original factory manual. That table will tell you exactly what thermostat Ford called for for your car with the engine you have.

But if you want to skip looking for the table, it's probably a Ford (Motorcraft) 192-195*F thermostat :)

I currently have a Motorcraft 192*F thermostat in my car that has been with me for many, many miles. I have had three Stant thermostats fail on me in a few years flat prior to swapping to the Motorcraft. So if you were looking for a brand recommendation, I'd put in a Motorcraft.
 

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Another way to go is to simply Google "the optimum operating temperature of a gasoline engine" and look at the first result. If you have a basic understanding of what a thermostat does then you don't have to be a mathematician to figure out you are probably not going to achieve that with an incorrect 180F thermostat. Personally, I LIKE optimum performance.
 
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