Engine Exhaust Cooling

When we first purchased our Nauticat late in 2006 I noticed that whenever the engine was running there was a constant stream of water “pissing” out of a small hole on the starboard side of the boat (just below the steps leading up to the outside steering station). The stream extended about 6″ when the engine was at idle and well over 12″ when the engine was running at 1200 RPM or higher. It looked like the stream you often see coming out of the side of an outboard motor – and strong enough for any man to envy ;).
I realized that this was a portion of the stream of water from the Jabsco water injector pump that passed through the transmission heat exchanger and then on to the engine exhaust and water muffler. There was lots of water coming out of the exhaust pipe at the back of the boat and there were no signs of the exhaust overheating so I figured everything was OK. I used the boat through the season in 2007 with no overheating incidents.
In the spring of 2008 I decided to check the impeller on the Jabso pump and found that several of the impeller vanes were very badly cracked so I replaced it with a spare that I had on board. The following spring (2009) I checked the impeller and it was very badly cracked – so once again I replaced it – but now I knew something was wrong because I had only put about 15 or 20 hours on the engine during the 2008 season and there is no way that the impeller should be that badly damaged in such a short time.
In the spring of 2010 I was preparing to take Ananda on an extended cruise and I did not want to run into trouble with the engine and related systems. I hired Ed Breen (Breen Marine), a marine mechanic in the Goderich area to go over the engine and all mechanical systems with me. I described the problem I was having with the Jabsco pump impellers and he suggested that the water injector in the exhaust elbow might be partially plugged.
First we checked the impeller for the Jabsco pump and it was once again very badly cracked – so we replaced it. When we removed the exhaust elbow – this is what we found! I made some quick inquiries on the internet to order a replacement elbow but found that it could take up to a month before I had a new one – and I was planning to leave on my cruise in two weeks!  Ed suggested that a local machine shop might be able to clean up the injector by sandblasting it. Unfortunately this did not work because the cast iron fitting was so “rotten” in spots that the sandblasting actually cut away a portion of the side of the fitting. The local machine shop wanted more money to fabricate a replacement fitting than a new one cost – and they could not guarantee that I would have it before I was scheduled to leave on my cruise. As a result, we decided to try to drill out the plugged portion of the injector.
Drilling out the injector collar was a tedious process but it was working. After about an hour (and several drill bits later) we had accomplished as much as we could hope for.
Here is a top view of the elbow and injector – after drilling was completed. The injector was looking pretty good (compared to what we started with) but you can see that parts of it were weakened by the years of corrosion.
Here is a side view of the elbow showing the water injector fitting on the side.
Here is a view of the other side of the elbow. Note the repair made where the cracks in the bottom of the elbow were. We used plastic metal for this repair and it worked really well.
We reinstalled the elbow and started the engine to check for leaks, etc. Everything worked as well as we could have hoped for. The first thing I noticed was that the pisser stream that used to come out of the side of the boat was reduced to a dribble when the engine was at idle and increased only slightly when the engine was running at higher RPMs.
I was able to start my cruise with the repaired elbow. My intention was to order a replacement and install it along the way. However, that never happened until a year after I arrived at my destination in Saint Andrews, New Brunswick – over 4,000 kilometers later. When I removed the old elbow it was in as good a shape as the day that Ed Breen and I refurbished it. I continued to check the Jabsco impeller each spring since 2010 and the one that I had installed in 2010 was still as good as new in the spring of 2014!
I have since learned that the “pisser” on the side of the boat is actually a vacuum break point to help prevent the exhaust from siphoning water back into the engine – but that it is not uncommon to see some water coming out of this vent when the engine is running.
I have also concluded that the Jabsco pump impellers were being damaged because of the exceptionally high back pressure on the pump – caused by the plugged water injector.

IMPORTANT NOTE: It’s critical that a small portion of the engine exhaust cooling water flows freely out of this “pisser” vent pipe when the engine is running. If it is plugged there is a very strong chance that when the engine is shut down, the residual heat from the engine will create a vacuum and suck water into the crankcase through the raw water intake. Keep a close watch on this fitting. Especially for spiders and mud wasps because they love to get into small spaces like this!