The heat exchanger keeps engine coolant and raw water separated while transferring heat between them. Scale, salt, corrosion products, zinc fragments and old impeller pieces can restrict raw-water tubes. Coolant-side deposits or depleted inhibitors can attack internal metals.
Inspection clues
- Rising temperature at a familiar rpm
- Reduced or steaming exhaust-water discharge
- Coolant pushed into or out of the expansion bottle
- Salt crystals around end caps or hose joints
- Oil in coolant or coolant in oil
- Corroded end caps, cores or internal anodes
Cleaning method depends on construction and deposits. Aggressive chemicals can damage copper alloys, aluminium, seals and solder. Follow the engine or exchanger maker’s process, neutralise and dispose of chemicals correctly, and pressure-test if leakage is suspected.
Use approved coolant mixed with suitable water and at the specified concentration. Mixing incompatible coolants can create sludge or reduce protection. Renew caps, O-rings and gaskets as required, then bleed trapped air using the model procedure, especially when a calorifier sits above the engine.
An overheating problem that remains after raw-water service may be caused by a thermostat, circulating pump, head-gasket leak, blocked exhaust, incorrect sender, overloaded propeller or air trapped in the closed circuit.