What engine fluid is indicated by an orange stain?

An orange stain is indicative of anti-freeze, which is also known as coolant. Anti-freeze is used in the engine cooling system to prevent the engine from overheating and to protect it from corrosion. The orange color often comes from the specific additives used in the coolant, which can be a mixture of ethylene glycol or propylene glycol.

When diagnosing engine fluid leaks, it's essential to identify the color and consistency of the fluid to determine what type it is. While other fluids may resemble anti-freeze in viscosity, their colors are typically different—transmission fluid is usually reddish or pink, power steering fluid can be clear or slightly amber, and brake fluid is often yellowish or clear. Recognizing the distinct characteristics of anti-freeze is crucial for addressing issues in the vehicle's cooling system effectively.