One afternoon, I hooked up my Mercury to flush it after fishing and… nothing. No water coming out of the telltale. My heart sank, because that little stream is your motor’s lifeline. Here’s what I’ve learned about troubleshooting when your Mercury won’t flush water.
- Check the Hose and Muffs
More than once I’ve had the muffs not seated properly, or the water pressure was too low. Before assuming it’s serious, I reseat the muffs, crank up the hose pressure, and try again. - Inspect the Tell-Tale
Sometimes the outlet gets clogged with mud daubers, salt, or debris. I carry a piece of weed-eater line and gently poke it into the hole. That’s cleared the issue for me several times. - Look at the Water Pump Impeller
If neither of the above works, the impeller might be worn or damaged. I had one fail after just two seasons in brackish water. Replacing it is a bit of work, but it’s cheaper than cooking a motor. - Check the Thermostat
On one occasion, my thermostat was stuck closed, preventing proper circulation. I pulled it, dropped it in boiling water to test it, and sure enough — it wasn’t opening. - Don’t Keep Running It
The biggest mistake is letting the engine run without water flow. I shut mine down immediately if there’s no steady stream.
Most of the time, it’s something simple like clogged muffs or a blocked telltale. But if you’ve tried the basics and still no water, it’s time to service the water pump.