I'm in the process of cleaning my HX and mixing elbow on my perkins 4-154. I am also re-routing some exhaust lines as a result of moving my muffler. While doing this work I noticed that, on my boat, there is a vented loop in the waterline between the HX and the mixing elbow. There is also a large vented loop in the exhaust line immediately after the muffler. Is the vented loop and extra hose needed between the HX and the mixing elbow? Wouldn't the loop in the exhaust line keep water from back siphoning through the HX? Perhaps it is needed to keep dirty exhaust water from being back-siphoned from the waterlift muffler. Is that possible with a vented loop in the exhaust?
YES! You have two different paths. If the intake does not break a siphon it keeps filling the exhaust elbow until it backs up into the engine regardless of the fact that you may have a siphon break on the exhaust.
This has happened to many a sailor. Depending upon how your wet exhaust is routed & where it terminates you may or may not need one but they are never a bad idea. A rough following sea can often start a siphon in the exhaust hose and you get the same result as from the intake side..
There are some builders who cheaped out and did not use them on the RW intake and many owners have paid for these builder short cuts. The most important one IMHO is on the RW intake before the exhaust elbow.
Installing an engine in a sailboat without a siphon break on the intake is like going to Vegas. You might win for a while but you eventually lose.
Oh and RW pumps are NOT shut off valves and they often leak by which is why engine manufacturers recommend siphon breaks on the intake.
