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Marine Exhaust & Cooling Systems
The cooling and exhaust system is what keeps a marine diesel alive. Failures are usually preventable but consistently inconvenient — overheating in a tight anchorage, exhaust leak filling the engine room with carbon monoxide. Understanding the system and maintaining it on schedule prevents most problems.
The system components
- Raw water intake: Through-hull, strainer, hose to pump.
- Raw water pump: Impeller-driven, drives sea water through the system.
- Heat exchanger: Where the closed-loop engine coolant gives up heat to the raw water.
- Engine block coolant: Antifreeze in a closed loop, circulated by belt-driven pump.
- Exhaust mixing elbow: Where raw water joins exhaust gas to cool it.
- Wet exhaust hose: Carries the cooled exhaust + water aft.
- Muffler: Water-lift or separator.
- Exhaust outlet: Through-hull, typically transom-mounted.
Maintenance schedule
| Item | Interval | Notes |
|---|---|---|
| Impeller replacement | Annually | Preventive; always carry spare |
| Heat exchanger zinc | Annually | Critical anode |
| Heat exchanger chemical clean | 3–5 years | Bundle pull + clean |
| Coolant change | 2 years | Per engine manual |
| Exhaust elbow inspection | 2–3 years | Pull and inspect |
| Exhaust elbow replacement | 5–10 years | Saltwater corrosion |
| Raw water hose inspection | Annually | Check for cracking |
Common costs
| Service | Common range (USD) | Notes |
|---|---|---|
| Impeller + service | $50–150 | DIY parts; pro labour add $100 |
| Heat exchanger zinc | $20–40 | Annual |
| Heat exchanger full service | $300–800 | Pull + clean + parts |
| Exhaust elbow replacement | $400–1,500 | Engine-dependent |
| Coolant change | $80–200 | Parts + labour |
| Full cooling system overhaul | $1,200–3,000 | Major work |
Frequently asked questions
Why does cooling fail?
Blocked intake, failed impeller, clogged heat exchanger, corroded exhaust elbow.
Exhaust elbow life?
5–10 years typical. $400–1,500 replacement.
Heat exchanger service?
Every 3–5 years; zinc annually. $300–800 full service.
Impeller?
Annual replacement. Always carry spare.
Where to service?
Any competent diesel mechanic. Often DIY.