2006 Ford F-350 Freeze protection

You can use either one of them below

There are two devices used to check antifreeze strength"”the antifreeze hydrometer and the refractometer. The antifreeze hydrometer is used to measure the freezing point of the cooling system. A squeeze and release bulb draws coolant into the tester, and a needle floats to show the freeze protection point. With the refractometer, you draw coolant into the tester. Then place a few drops of coolant on the measuring window (surface). Aim the tester at a light and view through the tester sight. The scale in the refractometer indicates the freeze protection point. Minimum antifreeze strength should be several degrees lower than the lowest possible temperature for the climate of the area. For example, if the lowest normal temperature for the area is 10oF, the antifreeze should test to -20 °F. A 50/50 mixture of antifreeze and water is commonly used to provide protection for most weather conditions.