Final answer:
The mixing of water with a lubricant typically decreases the lubricant's viscosity, potentially leading to inadequate protection for engine parts at higher operating temperatures. Water's lower viscosity relative to oil's long-chain molecules results in a thinner and less effective lubricant when combined.
Step-by-step explanation:
When water is mixed with lubricating oil, the viscosity of the lubricant is likely to decrease. This is because the molecular interactions that give oil its high viscosity are disrupted by the addition of water, which has much lower viscosity than oil. The lower viscosity results because water molecules are smaller and less able to become entangled with the longer-chain oil molecules that contribute to higher lubricant viscosity.
It's important to note that for applications like motor oils, having a controlled viscosity is crucial for the oil to function effectively as a lubricant. The oil should be fluid enough to cover engine parts at low temperatures, yet thick enough to provide sufficient lubrication at high temperatures. The presence of water can lead to a viscosity that is too low to protect the engine effectively, especially at higher operating temperatures.
Furthermore, water contamination can also lead to other issues such as rust and corrosion within an engine, further highlighting why it is undesirable for water to mix with lubricants like motor oil.