How water back flow into the engine cylinder?

[jp]

I know for some reason(s) the raw cooling water can back flow into engine clinders during fail starting. Can anyone tell me how this happened? Is this aplly to both gas and deisel engine? How do you prevent this from happenning?Thanks for your attention!

 

[Dave Emery]

Bad Thing

Your engine has a pump that moves raw water through the heat exchanger to cool the fresh water circulating in your engine. The raw water is then discharged into a water lift muffler. The raw water is then expelled from the water lift muffler when exhaust from your engine enters the water lift muffler. Together they exit above the water through a through hull, typically on the transom. If you continue to crank your engine over with out starting, raw water is pushed into the water lift muffler, but insufficient exhaust pressure exist to push it through the the waster lift muffler and out of the boat. The water will continue to fill the muffler and will eventually rise up the exhaust system, entering the engine cylinders. In order to prevent this, there is a peacock value at the base of the water lift muffler. If your engine doesn’t start in a reasonable time, you should bleed the excess water from the water lift muffler.

 

[Peter J. Brennan]

Following seas

can also enter the exhaust pipe and get to the engine in the same manner, through the water lift muffler. If you will be sailing downwibnd for a long time, a plug in the port or a flap over it can help. Manual on my engine (Universal 4 cylinder) specifically warns against cranking the engine for too long because of the danger of water entering the engine. Not good for the starter either.

 

[RonD]

Raw Water Accumulation

Regarding the two prvious posts:1. Don't crank the engine for more than 15-20 seconds. If it doesn't start, FIND OUT WHY AND FIX THE PROBLEM! Drain the water lift muffler before trying again. Most likely problems: lack of fuel (clogged filters, air in fuel system, bad fuel pump, injector, etc.) or a bad glow plug (or its wiring).[Incidently, excessive cranking can really ruin the starter, too. It can overheat to the point of melting solder and wiring insulation.]2. A following sea shouldn't cause any water accumulation in the muffler if the boat is equipped with an anti-siphon loop in the exhaust.The water lift muffler is generally mounted below the engine, and the seawater/freshwater heat exchanger high on the engine for a good reason -- to keep seawater from backing into the engine (generally the oil sump).--Ron