Why is my Mercury outboard not peeing water?
My Mercury outboard starts normally, but there's no water coming from the little outlet under the cowling. How do I check whether it's just blocked or the water pump has failed, and is it safe to keep running?
Answer
Your Mercury outboard may have a blocked tell-tale outlet, an inadequate water supply or a faulty water-pump impeller. Stop the engine, check the intake and water supply first, then inspect the tell-tale before running it again.
Check the pump's water supply
The tell-tale is the small cooling-water outlet, usually beneath the rear or side of the cowling. It shows water flowing through part of the cooling circuit. A missing stream does not prove the pump has failed; a strong stream does not guarantee the whole engine is cooling properly.
Switch off, remove the kill cord and keep hands clear of the propeller before clearing intakes or removing covers.
- Afloat: lower the engine into its normal operating position. Check the gearcase intake grilles for weed, mud, sand or a plastic bag.
- In a barrel: water must reach above the water-pump housing, not just cover the intake grilles. The pump sits above the gearcase. A shallow bucket can leave it unable to prime.
- On flushing muffs: check that they suit your gearcase, seal over the required intakes and receive enough water from the hose. Some Mercury gearcases have additional intake openings that need a specific flushing arrangement.
Never start the engine dry, even briefly. The rubber impeller needs water for lubrication. Follow the flushing instructions for your exact model; a threaded hose-flushing connection does not automatically permit running the engine.
Clear the tell-tale and hose
If the water supply is adequate, check the small outlet for salt crystals, grit or an insect nest. Its narrow opening can block while cooling water still circulates elsewhere.
- With the engine stopped and cool, gently probe the outlet with thin nylon strimmer line that fits freely.
- Remove the cowling and trace the small tell-tale hose. Look for kinks, splits, a loose connection or debris.
- If accessible, disconnect the hose at the outlet fitting and clean the fitting separately. Refit the hose securely before testing.
Avoid drill bits, stiff wire and high-pressure compressed air. They can damage fittings or drive debris further into the circuit. Water leaking inside the cowling can indicate a detached or split hose.
After clearing a definite blockage, test briefly at idle with the correct water supply. If flow does not start promptly, shut down. Do not keep restarting or revving the engine to encourage a stream.