Remove the radiator cap.

The engine must be cool before removing the radiator cap, or severe scalding may result.
Test the coolant mixture with a hydrometer (see below for "Coolant specific gravity chart").
For maximum corrosion protection, a 1:1 solution of ethylene glycol and distilled water is recommended (page 6-4).
Look for contamination and replace the coolant if necessary.

Coolant specific gravity chart
Coolant temperature°C (°F) | |||||||||||
Coolant ratio % | 0 (32) | 5 (41) | 10 (50) | 15 (59) | 20 (68) | 25 (77) | 30 (86) | 35 (95) | 40 (104) | 45 (113) | 50 (122) |
5 | 1.009 | 1.009 | 1.008 | 1.008 | 1.007 | 1.006 | 1.005 | 1.003 | 1.001 | 0.999 | 0.997 |
10 | 1.018 | 1.017 | 1.017 | 1.016 | 1.015 | 1.014 | 1.013 | 1.011 | 1.009 | 1.007 | 1.005 |
15 | 1.028 | 1.027 | 1.026 | 1.025 | 1.024 | 1.022 | 1.020 | 1.018 | 1.016 | 1.014 | 1.012 |
20 | 1.036 | 1.035 | 1.034 | 1.033 | 1.031 | 1.029 | 1.027 | 1.025 | 1.023 | 1.021 | 1.019 |
25 | 1.045 | 1.044 | 1.043 | 1.042 | 1.040 | 1.038 | 1.036 | 1.034 | 1.031 | 1.028 | 1.025 |
30 | 1.053 | 1.052 | 1.051 | 1.047 | 1.046 | 1.045 | 1.043 | 1.041 | 1.038 | 1.035 | 1.032 |
35 | 1.063 | 1.062 | 1.060 | 1.058 | 1.056 | 1.054 | 1.052 | 1.049 | 1.046 | 1.043 | 1.040 |
40 | 1.072 | 1.070 | 1.068 | 1.066 | 1.064 | 1.062 | 1.059 | 1.056 | 1.053 | 1.050 | 1.047 |
45 | 1.080 | 1.078 | 1.076 | 1.074 | 1.072 | 1.069 | 1.066 | 1.063 | 1.060 | 1.057 | 1.054 |
50 | 1.086 | 1.084 | 1.082 | 1.080 | 1.077 | 1.074 | 1.071 | 1.068 | 1.065 | 1.062 | 1.059 |
55 | 1.095 | 1.093 | 1.091 | 1.088 | 1.085 | 1.082 | 1.079 | 1.076 | 1.073 | 1.070 | 1.067 |
60 | 1.100 | 1.098 | 1.095 | 1.092 | 1.089 | 1.086 | 1.083 | 1.080 | 1.077 | 1.074 | 1.071 |