When any material has a high specific heat capacity/ heat capacity, it doesn't heat or cool very fast. So water can absorb more heat from the engine and can keep the engine cool or at low temperature for a longer period of time.
Using Gay-Lussac's Law, pressure is proportional to (absolute) temperature in Kelvin. We first convert the temperature values to Kelvin: 110 C = 383.15 K, while 65 C = 338.15 K. P1/T1 = P2/T2 22.5/383.15 = P2/338.15 P2 = 19.9 psi
