High cooling-water temperature approaching Baja lock
You are master of an 85 m motor cargo vessel with a 1,100 kW diesel main engine, proceeding downstream to Baja lock at 75% load. The engine has a closed freshwater cooling circuit and a raw-water heat exchanger. Outside air is 34 °C; river temperature 26 °C. Five kilometres before the lock, the high-temperature alarm sounds at 98 °C, the expansion tank level is below the minimum mark, and the exhaust shows light white vapour. The raw-water strainer was cleaned two days ago. The engine room is hot; the auxiliary generator is running. There is a safe anchorage 1.2 km ahead on the right bank, but the current sets toward a gravel bank. The lock queue is 40 minutes. You have one engineer on board; the other crew are deckhands. The engine manufacturer's limit is 95 °C continuous, and the alarm resets only after cooling. You smell no fuel or exhaust gas in the coolant.
1. What are the likely causes, and which checks do you make before deciding to stop?
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Likely causes are loss of raw-water flow, loss of coolant, or a heat-transfer problem. I would check the raw-water inlet and strainer first, even though it was cleaned two days ago, because a plastic bag or a broken impeller vane can block flow quickly. I would check the raw-water pump and belt, look for leaks around the heat exchanger and hoses, check the coolant level and for air locks, and feel the heat exchanger for a large temperature difference. The white vapour may be steam from a coolant leak or from raw water boiling, not necessarily unburnt fuel. I would not open the expansion-tank cap while the engine is at 98 °C. I would use an infrared thermometer or the gauges to compare the block and outlet temperatures, and I would reduce engine load immediately to lower heat input while I diagnose.
2. Do you continue to the lock or anchor? Explain the risk trade-off.
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I would not continue to Baja lock at 75% load. The manufacturer's continuous limit is 95 °C and the alarm is already at 98 °C, so the engine is outside its limit and a seizure or head-gasket failure could leave me without power near the lock approach. The anchorage 1.2 km ahead is the better option, but the current sets toward a gravel bank, so I would reduce load to the minimum needed for steerage, head for the anchorage at a safe angle, prepare the anchor, and keep the engine running only while it can be monitored. I would inform the lock and the port authority of the problem and ask for priority or assistance if needed. If the temperature continues to rise, or coolant level falls again, I would stop the engine and anchor rather than risk a breakdown in the lock approach. Continuing to the lock queue would mean waiting 40 minutes with a hot engine and no safe repair space.
3. The engineer reports the raw-water pump impeller has lost three vanes. You have a spare. What do you do, and what operational limits until repair?
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With a safe anchorage or berth secured and the engine stopped, I would close the raw-water seacock, isolate the pump, replace the impeller, and account for all broken vanes. Missing vanes may have travelled downstream, so I would open the heat-exchanger end cover and the strainer and remove any debris. I would check the pump cam and wear plate, refill the coolant circuit with the correct mixture, vent the circuit, and run the engine at low load while watching temperature, raw-water flow, and exhaust. I would not enter the lock until the engine has held normal temperature at working load and the engineer confirms the repair. If the spare does not restore flow, or if the coolant is contaminated with oil or exhaust gas, I would keep the vessel at the berth and arrange assistance.