Originally Posted by bvander66
Dont recommend marelon vented loops in the exhaust water, should be metal. Exception is Vetus makes an exhaust quality plastic/grp one.
Vented loops/siphon breaks/vacuum breakers are inserted into the raw water intake side of the system not generally into the "exhaust" system.. The water is still cool before it enters the RW exhaust injection elbow. There are literally thousands upon thousands of vessels out there with Marelon siphon breaks to protect the RW circuit from a siphoning event. While I am not a huge fan of the "duck bill", and generally prefer the Scot break, they work fine for an engine siphon break and are specifically sold for that as one of the intended uses...
Beyond that Marelon is the only plastic I know of to pass the stringent USCG fuel valve burn test. A Marelon valve sustained temps to 1275 degrees with the majority of the burn test time being between 850f & 980F. The valve did not leak any gasoline and passed the tests. If you hit anywhere close to these temps in a wet exhaust system, especially on the RW injection side, you have much bigger problems to worry about..