Troubleshooting an overheating engine

Hugh Morrison works his way through a comprehensive checklist to trace the source of an overheating problem in a Mercedes OM636 engine

The venerable old Mercedes OM636 engine in Astonel, our 10.9m (36ft) bilge-keel Westerly Solway, has put up with a great deal in the four years we have owned the boat. What happened to us on a return passage across the Channel could happen to anyone. After leaving Cherbourg, the high-pitched but rather distant sound of an alarm penetrated my consciousness, and although the gauge showed some increase in temperature it was within limits. But the locker under the cockpit seat, where the header tank is mounted, had become a sauna as a joint in the feed from the Bowman heat exchanger to the header tank had come apart. We had been motor-sailing and were a couple of miles out of the harbour. We turned back, and with the engine turning…

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Practical Boat Owner (Digital) - 1 Issue, June 2015

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