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Providing they are regularly serviced and maintained, modern marine diesel engines tend to be very reliable. However, they are by no means infallible and a large percentage of lifeboat rescues are to leisure vessels with engine failure. Fortunately, a handful of easily rectified problems are responsible for a high percentage of engine failures. These can normally be fixed in a few minutes with a relatively small amount of knowledge, a few simple tools and by carrying a small number of inexpensive spares.

Many engine failures are caused by lack of maintenance, resulting in fuel filter blockages, water pump failures, overheating and other breakdowns. Indeed, one of the most common reasons for marine rescue service call outs is for one of the most basic reasons possible – boats that have run out of fuel. One of the golden rules is to always check the fuel tank levels before setting out and to carry reserve fuel in case it is needed.

engine failure at sea

Another common situation is one in which sediment that would otherwise sit (apparently harmlessly) on the bottom of the fuel tank is shaken around in a rough sea and then sucked into the fuel system, blocking the filters. It’s also possible for bacteria that will eventually clog fuel filters to form in diesel tanks, although again effective maintenance will minimise the risk of this.

Engine failure – when the alarms buzz

To prevent the risk of serious damage, immediate action must be taken if an engine alarm sounds, even if the motor continues to operate. Take the engine out of gear and check which warning light is lit up, with the motor idling in neutral.

The engine should then be shut down while you attempt to fix the problem. Note that, although there are warning lights for low oil pressure, overheating and lack of battery charging, on most engines an alarm will not sound for the latter fault.

boat primary filter

The rationale behind this is that it’s not a problem that must be immediately dealt with to avoid damage to the engine, although of course it could result in the batteries running flat within a relatively short length of time.

boat fuel filter

If your engine fails or is overheating there are a number of things to check immediately:

  • Air filter blocked – check, clean or replace.
  • Cooling water low – fill when engine is cold. Check for leaking hoses.
  • Exhaust pipe blocked or partially blocked.
  • Fuel filter – a blockage reduces power and can stop the engine. Check, clean or change the filter.
  • Lack of lubrication – check engine and gearbox oil levels.
  • Oil filter blocked – replace.
  • Raw water inlet filter – a blockage causes overheating and can lead to engine failure. Close seacock, check and clear filter. Re-open seacock. Check object (eg. plastic bag) is not obstructing seacock.
  • Water pump impeller failure – cooling system fails and engine overheats. Check the rubber impeller is slightly flexible, not hard, and that all the vanes are intact. Replace if necessary.
  • Worn alternator or water pump drive belts – replace if they are frayed or shiny.

boat impellor

Tips to avoid engine failure:

  • Keep the engine regularly maintained.
  • Always do engine checks before setting out.
  • Check fuel and oil levels regularly (don’t rely on gauges!).
  • Check drive belts for wear and tightness.
  • Look out for oil and coolant leaks.
  • Check fuel filter for water or dirt. Drain off any contaminants until the fuel in the clear glass bowl by the filter is clear.
  • Learn how to bleed the fuel system if air gets into it.

Happy boating and stay safe on the water!

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