* Overfilled Reservoir: This is the simplest explanation. If the reservoir was overfilled, the heat from operation expands the fluid, causing it to overflow when the system cools down after shutdown.
* Internal Leak in the Power Steering Pump: A leak *inside* the pump can cause pressure to build up when the engine is running, but not be immediately noticeable as an external leak. When the engine stops, the pressure is released back into the reservoir, forcing fluid out.
* Faulty Pressure Relief Valve: This valve is designed to release excess pressure. If it's malfunctioning or stuck closed, pressure will continue to build even after the engine is off, eventually forcing fluid out.
* Restricted Return Line: If the return line from the power steering rack or gear is restricted (due to blockage, kinks, or damage), the fluid can't return to the reservoir quickly enough. This causes pressure to build up and overflow when the engine stops.
* Problem with the Power Steering Rack and Pinion: A severely worn or damaged rack and pinion can create excessive internal friction, leading to higher pressure. This extra pressure could overflow the reservoir after shutdown.
What to do:
1. Check the fluid level: Make sure it's within the "cold" fill line on the reservoir. If it's overfilled, simply remove some fluid.
2. Inspect for leaks: Carefully examine all power steering hoses, connections, the pump itself, and the rack and pinion for any signs of leaks (wet spots, fluid dripping).
3. Check the power steering belt: Ensure the belt is properly tensioned and in good condition; a slipping belt could cause the pump to struggle and build up pressure.
4. If no external leaks are found: It's likely an internal problem within the power steering pump, pressure relief valve, or rack and pinion. This requires professional diagnosis and likely repair or replacement.
Caution: Power steering fluid is under pressure even after the engine is off. Always take precautions to avoid burns or injuries when inspecting the system. If you're not comfortable working on your car's power steering system yourself, take it to a qualified mechanic for diagnosis and repair.
