What engine fluid is indicated by a green stain?

A green stain on the ground under a vehicle typically indicates a coolant leak. Coolant, which is essential for regulating engine temperature, often contains dyes to help in identifying leaks. In many vehicles, a green dye is used specifically for this purpose, making it easy to recognize when coolant is leaking from the system.

Understanding the role of coolant is important because it helps prevent the engine from overheating. If this fluid is leaking, it can lead to serious engine damage if not addressed promptly. Recognizing the signs of a coolant leak early is crucial for maintaining vehicle health and ensuring safe operation. While the other fluids listed (washer fluid, transmission fluid, and oil) may also exhibit color traits, they do not typically show as a green stain, which is why coolant is the best answer in this scenario.