Mark Turner:Hi! My name is Mark Turner; I am the Fleet Service Director with Offshore Sailing School. We are here in Southwest Florida of the beautiful South Seas Island Resort. What I would like to talk you about today is one of the most common problems we have with diesel engines on the sailboats and that is overheating, reason being we are dealing in power with water from outside the boat which we have little control as to have been contaminant free. These contaminants come in a number of forms, some even quite lively, most in the shape of seagrass or seaweed.
At the outset, check the composite parts of the raw water system able to perform that duty. Is the raw water intake valve open? Is the raw water filter clear? Do we have a healthy flow of water out of the exhaust when we start the engine? If the answers for these three checks are all yes, then we have no initial cause for concern.
When monitoring the vitals of a diesel engine while it's running one of the most important things to consider is temperature. If you have a gauge keep an eye on it from time to time to make sure it's with in normal working parameters. Some helm stations don't have a temperature gauge but do have warning lights and buzzers. If you notice the engine temperature is starting to rise, the first consideration should be is that still good water flow out of the exhaust. If yes, then may be a problem with the fresh water portion of the system. This may be a little harder to diagnose but is often very evident when you inspect the engine. If no, or you feel the exhaust is a little more throaty sounding then it's probably time to check the raw water system. Check the filter first, although a quick look to make sure the intake hasn't being clogged won't hurt. If the filter looks clear don't be lured into a sense of false security; you need to make sure there is good flow from the intake to the filter. Blockages are common in that hose particularly if there is an elbow in the line. One simple check is to close the intake valve, open the filter and quickly open the intake valve and check for good water flow at the filter. If you don't see good water flow, work back through the system to find the blockage this will involve disconnecting hoses to makes sure there is flow, start the intake, then move forward. Common culprits will be the intake itself and some larger weeds can be cleared with the creative use of an air-horn. If everything seems clear that could also be a blockage at the point of entry at the filter. If everything seems clear to the filter, its time to look upstream, check the impeller, watch out as a broken impeller is often a symptom not a cause.
If you have to replace the impeller then check everything is clear downstream before re-starting the engine. If you can't piece together the impeller then you need to find the bits, this starts to get more complicated, but a short fact will help to suck out any missing pieces. If after all those checks you are still having problems with the water flow it's probably time to call someone like myself that has a little bit more expertise. 1