Question: I’m finally in the process of winterizing my boat and I just noticed something that is a little troubling to me. My Yanmar diesel is equipped with a waterlift type muffler in the exhaust system but it has no drain in the base of it. I’ve been told by ABYC Certified techs that a drain is required under the ABYC Standards, but my boat doesn’t have one. Do I need to worry about this?
Answer: The ABYC Standard that addresses exhaust systems does require a drain for this type of muffler. That said, I’ve seen plenty that don’t come equipped with one. You have several options here. One is to remove the muffler and drill and tap a drain fitting into the lowest section of the cylinder that you get to conveniently. If you opt for this approach, be advised that the wall thickness on the muffler may not be adequate to support tapping threads into effectively. I can see from the photo you sent in that the muffler is made of spun fiberglass and not high temperature plastic like others I’ve seen. Those units do not have adequate wall thickness to tap threads into I can assure you. Yours may. If not, since it is fiberglass, you could drill a hole, and add some thickness by epoxy gluing a small 1/2″ thick piece of delran or similar plastic sheet to the outside of the canister and then drilling and tapping it to accommodate an appropriately sized pipe plug to facilitate draining each year.
If all that seems like more than you want to tackle, you can winterize the exhaust system by warming up the engine and then removing the raw water intake hose and running the engine while pouring a potable anti-freeze solution through the raw water cooling system. Once you see anti-freeze tainted cooling water being pumped out the exhaust pipe, you will be all set as far as a potential freeze-up in the exhaust is concerned.