Isn't that anti-siphon on the exhaust?
I can't figure how you could have an anti-siphon valve (commonly called a vented loop) between the thru-hull and the cooling water pump on the intake side. Basically, you can PUSH water over a vented loop, but you can't PULL it from the far side, where the pump would be. The flow of raw cooling water is from the thru-hull to the strainer to the pump to the heat exchanger and then to the mixing elbow, where it is used to cool/quiet the engine exhaust. For proper, safe operation, you MUST have a vented loop in the line between the heat exchanger and the mixing elbow. This will prevent water being siphoned from the intake thru-hull into the exhaust (yes, water CAN be siphoned through the raw water pump impeller) when the engine isn't running and the potential exists for it to get into the engine. In addition, you should have a loop (no vent required) in the exhaust hose between the mixing elbow and the exhaust port in the hull of the boat. Cleaning a vented loop depends on its specific design. They all have a moving part, either rubber, plastic or metal, which seals when water is being pushed through the loop and opens when it is trying to 'pull' or siphon. Cleaning it is a matter of making sure the moving part is free to move when it needs to. On the vented loop in my head, I can actually hear air being sucked through the valve after I pump water up over it and it is falling down into the holding tank. That probably won't work for the engine loop. Finally, older Hunter 27s usually had 10hp diesels in them, often a Yanmar. However, any 20 year old or older boat may well have been re-powered at some time, so you'd have to identify your engine by its data plate. New 27s have a larger Yanmar in them. Cheers, Bob s/v X SAIL R 8
