Troubleshooting a Diesel Engine

By Capt. Grant Rafter

Troubleshooting a dead diesel engine requires a little bit of knowledge on what keeps a diesel engine alive. Clean fuel and air are necessary elements to a running an engine. Always start your troubleshooting by checking for the basic, simple causes for engine failure.

Engine has failed to Start

1. Check the ignition. The problem can be as simple as the key switch or breaker not being in the right place.

2. Check the starting system. Gauges do not have 100-percent accuracy, so it is important to check your starter battery’s charge. Use a voltmeter if available. Otherwise, use a portable multimeter to check each individual battery.

Note: When batteries are parallel or in a series make sure to remove batteries from their connecting battery cables so that an individual battery reading is produced rather than a single reading of the entire battery bank.

Starter battery is low:

1. Check for a battery-parallel switch and flip it to bring house batteries online.

2. If no battery-parallel switch is available, use automotive jumper cables to jump starting battery from a different battery.

3. Use an available genset to charge the battery with an onboard battery charger. The battery will not charge, however, if the issue is a shorted battery. A shorted battery can affect the other batteries so make sure to disconnect its cables immediately.

If the starter battery is not low:

1. Use your multimeter to check the battery/starter terminals for loose connections to the starter.

2. If both terminals prove to be tight, then the issue may be a bad starter motor or a bad solenoid and you will need a licensed mechanic.

Engine turns over but won't start

1. Check the fuel level. This is done at the sightglass or dipstick and at the gauge.

2. Check level of fuel in the clear bowls located in the fuel-water separators. If they are empty, this means your engine is empty as well.

If there is fuel to the separators and engine is still dead:

1. The issue could be a fuel system leak. For this you will need to refer to your manual on how to bleed air from the diesel engine.

2. Dirty fuel may be the issue. While you are at the fuel-water separators, make sure the fuel color is amber or clear red. If the fuel has a dark color, be sure to drain the separator and refill with clear fuel. Then, immediately replace the filter element.

3. Finally, check the filter. Black exhaust and a dirty filter can affect the air supply.


Three components keep the engine from overheating: oil, coolant, and sea water. Should the engine-temperature alarm go off; it is time to back off the throttle.

1. Check the exhaust. If the stream of water coming out is not a smooth stream than there may be clog in the sea strainer.

2. Check the seacock to make sure it is completely open.

3. Check the sea strainer. The strainer should contain water. If not, you will need to jump out of the boat and check what may be blocking the through-hull located on the boat’s exterior.

If the strainer has plenty of water, than the issue may be a fried raw-water pump:

1. Check coolant level and disassemble the pump if the impeller is fried.

If the raw-water looks okay, there could be a lack of coolant:

1. Make sure to wait until the engine has cooled to check.

2. Refill coolant. If there isn’t extra coolant available, add fresh water until you are able to replenish with coolant.

3. Be sure to check hoses thoroughly for any holes that could be disrupting the coolant flow. Water in the bilge would be an indication that the hose has a hole.

If all elements above pass their check, the problem could be Overloading.

1. You will see that Overloading is the problem if the rpm drops along with a high reading from the thermostat. This will require a full inspection of the boat’s exterior.

Any problems beyond the possibilities listed above:

1. Call a Mechanic; and maybe TowBoatUS

Originally Published by Power & Motoryacht - January 2014

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