Geoff Stevenson, a former C320 owner who now owns a C350, called me after reading the May Mainsheet to point out another possible reason for a hot-running engine. He reminded me of the “recall” on certain Yanmar 3YM engines to correct an inadequately engineered cooling tube array. His experience (on both boats) was an inability to reach max power settings and chronic overheating.
These early (2004/2005) engines have a 38-tube heat exchanger, and some very early engines were reportedly also fitted with a smaller capacity raw water pump than is now used. The fix is to replace the original 38-tube heat exchanger core with a new 63-tube one, and change the water pump if necessary.
If you have a 3YM engine exhibiting similar problems, you may want to check with Yanmar to see if your engine is covered under their (silent) recall, especially if you have an engine serial number under 6,000.
– Karl Mielenhausen, Silver Lining, #690