Avoid These 9 Common Diesel Engine Disasters

February 14, 2017 - 9:00 AM by Samantha Pudney

All skippers should establish a pattern of routine diesel engine checks to protect the quality, safety and longevity of their engine. The first checklist applies when the engine is stopped, while other tips apply once the engine is running.

These checks will only take a few minutes each and should be undertaken once every two to three days if you intend to use your engine regularly. For infrequent boating, check weekly in order to avoid these common diesel engine disasters.


1. Cooling Water Leaks

Water leaking from a hose or fitting over the engine will cause long-term damage and can affect the operation of any electrical equipment within range. Very little electrical equipment fitted to the engine is fully waterproofed. Terminals are especially vulnerable to corrosion and failure.

To make matters worse, drive belts tend to pick up the water from any leaks and throw it over the engine compartment. If you see a sign of a leak, try tightening the fittings immediately. If you discover the hose has failed, replace it as soon as possible.

Be considerate of any fittings sealed with low friction PTFE tape, which can be overtightened or cracked very easily when not handled with special care. Use a jointing compound or face seal as an alternative.

2. Stern Gland Leaks

A leaky propeller shaft seal or stern gland is fairly normal. A few drops per hour are no real threat, but the flow always tends to increase. It is better to stop any leaks in the early stages while you still have the chance.

Either, tighten the gland or force more grease in, but do not overtighten or put too much pressure on the greaser. This will cause wear of the propeller shaft.

3. Fuel Leaks

At best fuel leaks are messy, at worst they can stop your diesel engine. If the tank is below the engine then any fuel leak will result in air being drawn into the system while the engine is stopped. This will make it very difficult to start your engine!

Leaks can stem from the low pressure side of the system, the drain lines or the high-pressure side. Fittings used are normally sealed metal-to-metal or with sealing washers made from aluminium or copper.

Note: do not use a jointing compound or PTFE tape to seal fittings in the fuel system. It is virtually impossible to stop tiny particles entering the system and blocking the small, vital holes and valves in the pumps and injectors.

4. Oil Contamination

Diesel engines normally use a little more oil than petrol engines and the colour of new oil quickly becomes black. The dipstick indicates the level and condition of the oil.

If the level goes up and the oil is discoloured, this is a sign that it is contaminated with water. This could be due to a failure of a gasket or seal in the engine and will often involve a major repair.

Note: oil changes should always be made in line with the diesel engine manufacturer’s recommendations.


5. Drive Belt Slippages

Check with your finger to ensure that the belt movement is within the manufacturer’s recommendations. Drive belt slippages can cause a slow water pump and alternator speed. On the other hand, overtightening will reduce the life of their bearings.

6. Loose Engine Mountings

Check visually and then feel the mountings for yourself. Tighten any loose nuts, normally from the bottom, to keep the engine in alignment. Retighten the lock nut on top. If they are found to be loose, the engine may need to be realigned.

7. Exhaust Fume Leaks

Check the exhaust visually to see if there are any indicators of blowing, then tighten up the fitting or repair (or replace) the hose. If you do not, leaking exhaust fumes will quickly fill the boat, covering the engine and its compartment with a sticky, black soot.


8. Loose Electricals

Diesel engines do not need electrical power to run, but most need it to start and others, to stop. Many have an alternator or generator to charge the battery. Electrical and battery terminals can sometimes vibrate loose, so check they are secured well.

9. Water Leaks

Water leaks are often easier to trace when the diesel engine is running at operating temperature. On engines with indirect cooling, a leak between the coolant in the sealed system and the raw water from outside will generally cause water to overflow from the filler cap.

Normally, the leak will be in the heat exchanger. It will need to be cured when the engine is stopped. Best practice for system maintenance is to flush and refill the freshwater system of your diesel engine with the recommended water/antifreeze mix.