Do water pumps generally fail all of a sudden, or can they slowly stop working effectively?
My 99 Subaru Legacy recently started overheating on long-ish trips (> 25 min or so). I already replaced the thermostat, so I doubt that's (still) the problem. I also tried just taking out the thermostat and running water through it to see if the pump was working (and if the radiator was clogged). I put a hose in the top to keep it full, took off the top hose so I could see if water was pumping through, and started it up. To my surprise, the radiator filled up, and water started coming out of the top hose (from the engine)! Do I still need to replace the water pump, or should I check something else?