Keeping Those Engines Cool

Ed on Esprit de Mer reminded me as we departed Annapolis that we should be checking the engine mixing elbows where the engine cooling water is mixed with the exhaust gas to keep the exhaust cool. The combination of salt water with hot, corrosive exhaust gas creates an environment that eventually corrodes and clogs the exhaust mixing elbow.

I thought about the possibility and decided that there was a simple experiment that could be done to test whether there was a problem with the water flow through an engine. We took a bucket and held it under the exhaust to collect all the water that came out in a 15 second interval and measured the volume. The stbd engine volume was 1 gallon in 15 seconds, or 4 GPM. The port engine was 1/2 gallon in 15 seconds, or 2 GPM. Quite a difference!

At the next stop, we tore into the cooling system. The raw water impeller was in good shape. We found a couple of old impeller blades in the heat exchanger. The heat exchanger core looked good. The core is easy to remove on the Volvo Penta MD2040D engines, making it easy to check it.

We had not found enough to cause the difference in water flow. What about the water supply? I removed the hose from the sea cock and opened the sea cock. I expected to see a solid flow of water about 2 inches high. But there was a weak flow only about 1/2 inch high. I took a piece of solid house wire and probed through the sea cock. Out popped several large pieces of barnacle shell and the flow increased significantly - to the volume I expected. The photo shows the volume we had after the probing. The volume before was about a half inch high.

[Note: Lengths of house wire is great stuff to use for probing various areas of a boat or to retrieve items from narrow passages - I keep a couple of lengths on board in the tool bag.]

We reassembled everything and the engine now pumps 4 GPM, the same as the stbd engine. So now we have a baseline measurement on the performance of the raw water pumps and mixer elbows on both engines.

  -Terry

Update July 29, 2015: While talking with Alain, I realized that I had not recorded the engine RPM when we measured the water volume. It was while we were under way at cruising speed in the ICW, which is normally 2500-2800RPM.