Ninety percent of marine diesel failures trace to two systems: fuel and cooling. These guides cover both in depth — the impeller that keeps your engine from overheating, the bleed procedure that restarts a fuel-starved engine, the seven causes of overheating ranked by how often they actually occur, and the winterizing steps that prevent a cracked heat exchanger. Each article is written for the sailor who needs to handle the problem at sea or in the yard, without a diesel technician standing by.
Raw Water Impeller: Replace It Before It Fails
How the raw water cooling loop works, why impellers fail, the replacement procedure step by step, and the downstream damage a blown impeller causes if you ignore it.
- Replace every 1–2 years or 300 hours
- $15–40 part, 15-minute job
- Carry two spares and a cover gasket
Bleeding Air from a Marine Diesel
Why air stops a diesel cold, the fuel system path from tank to injectors, the bleed sequence for Yanmar and Volvo engines, and what to do when bleeding alone does not fix it.
- Bleed after running out of fuel
- Bleed after any filter change
- Practice before you need it offshore
Marine Diesel Overheating: Causes and At-Sea Fixes
The seven causes of overheating ranked by frequency, how to diagnose the problem at sea, the plastic-bag-over-seacock fix, thermostat bypass, and why you wait 30 minutes before opening the coolant cap.
- Stop engine immediately on alarm
- Check exhaust water flow first
- Plastic bag is the #1 cause
Winterizing Your Marine Diesel
The raw water circuit is the priority — it will crack if water freezes. The correct antifreeze flush method, fogging oil procedure, pre-storage oil change, and fuel treatment before layup.
- Pink RV antifreeze for raw water side
- Full tank prevents condensation
- Change oil before storage, not after
Related: Diesel Engine Fundamentals
New to your diesel? Start with the overview article covering why sailboat diesels fail, exhaust smoke diagnosis, zincs, and the five-minute pre-departure check that prevents most problems: What Every Sailor Should Know About Their Diesel →
About These Guides
These articles are practical references, not manufacturer service manuals. Procedures vary by engine model — always cross-reference with your engine's workshop manual, particularly for torque specifications and bleed point locations. Jabsco, Sherwood, Yanmar, Volvo Penta, and Beta Marine all have model-specific details that matter.