Join Date: Sep 2012
Location: Bremerton, Washington
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Exhaust Manifold Flooding with Cooling Water
I've read several cautions about excessive pre-start cranking potentially causing the exhaust manifold to flood with water, and I'm hoping someone can confirm my understanding of the physics behind this.
My engine is a raw water cooled Yanmar 2QM15, with the cooling water discharging into a mixing elbow, which connects to an exhaust hose, which runs through a water-lift muffler, through a loop under the deck, and then out the transom. The mixing elbow is about 18 inches above the waterline, but below the top of the loop.
My assumption is that prior to cranking, the level of water in the exhaust hose matches the water line. But during cranking (before the engine starts and pushes the water out the exhaust system), the cooling water collects in the hose until the water level eventually reaches the manifold, when it can run into the block.
Do I have the physics right here? How much cranking would it likely take to fill the hose? 30 seconds? 1 minute? (My engine takes about 15 seconds to start when it's cold). And if excessive water accumulates in the hose, is there a simple way to drain it out? (I guess I could temporarily drop the loop to allow gravity drain).