Specific Gravity Test

Measure the specific gravity of the coolant with a hydrometer.
Measure the coolant temperature and calculate the concentration from the relation between the specific gravity and temperature, using the following table for reference.

Fig 1: Checking Coolant With Hydrometer

Courtesy of HYUNDAI MOTOR CO.

Fig 2: Coolant Concentration Table

Courtesy of HYUNDAI MOTOR CO.

Example

The safe operating temperature is -15°C (5°F) when the measured specific gravity is 1.058 at coolant temperature of 20°C (68°F)

CAUTION:

If the concentration of the coolant is below 30%, its anti-corrosion properties will be adversely affected.
If the concentration is above 60%, both the anti-freeze and engine cooling property will decrease, affecting the engine adversely. For these reasons, be sure to maintain the concentration level within the specified range.
Do not mix types of anti-freeze.

Fig 3: Recommended Coolant

Courtesy of HYUNDAI MOTOR CO.