High Seas, Low Power: Diagnosing And Repairing An Underpowered Marine Diesel Engine
Posted on: 8 June 2017
If you own a boat any bigger than a simple rowing boat or coracle, it probably has a diesel engine fitted to it, from the small auxiliary engines used by yachts and sailing boats to the enormous, roaring outboard engines used by powerful, ocean-going motorboats. As you can imagine, keeping your engine in good working order at all times is vital for safe navigation of even the most placid waterways, and there are few mechanical problems a boat can suffer that are more unnerving (and potentially hazardous) as an unexplained loss of engine power.
If your boat's diesel engine does become underpowered, you will naturally want to repair it as soon as possible, but actually diagnosing the problem that is causing the power loss can be challenging; a wide range of factors can strip a diesel marine engine of power and functionality. Having the problem professionally diagnosed by marine diesel engine experts is always recommended. However, there are a few key problems that commonly cause mysterious power loss:
Overheating
A common cause of engine power loss, an overheating diesel boat engine is most likely caused by a damaged or malfunctioning radiator. Without the constant supply of cooling water that runs through your engine's radiator, heat build-up can quickly cause your engine to lose power, and may cause lasting engine damage if the engine is allowed to run for too long.
If your engine is running too hot, your first port of call should be your engine's water cooling lines. Check for any damage and/or leaks that may prevent water from cycling around your engine efficiently, and ensure that water levels are adequate for the size of your engine. If water levels are low, the filter that sifts contaminants from freshwater and seawater before it is used to cool the engine may be clogged, so you should have it cleaned or replaced as soon as possible.
Contaminated fuel
Keeping any and all contaminants out of your engine's supply of diesel fuel is vital to proper functioning, and a sudden loss of engine power is often caused by unwanted substances entering the fuel supply.
Air bubbles can be one of these contaminants; they can be drawn into your fuel supply via cracks and pinholes in your fuel lines, but a certain amount of air can still infiltrate the most tightly secured fuel supply during rough seas and high-speed runs. Most marine diesel engines feature air bleeders, which can be unscrewed to allow this unwanted air to escape — these can be operated using nothing more than a simple wrench, but you should have your engine bled professionally if you don't feel confident enough to bleed your engine yourself.
Another potential fuel contaminant is water, but this is a far more dangerous prospect than simple air bubbles. Water in your fuel supply can cause serious internal damage and cause your engine to overheat very rapidly. You will need to have the engine professionally inspected for any lasting damage that may occur.
Oil supply problems
This is one of the most dangerous causes of unexplained (and often sudden) power loss and is often accompanied by distinctive plumes of dark smoke from your engine. You may also notice some unusual 'grinding' noises, and your boat's oil pressure light (if it has one) will flash.
If you notice these symptoms, you should cut engine power immediately, as running a marine diesel engine that isn't properly supplied with oil can cause catastrophic internal damage remarkably quickly. Once the engine is powered down, check your engine's oil levels, and top up the oil reservoir if it is running low.
If your engine has an adequate supply of oil but is still showing symptoms of diminished oil supply, something is preventing the oil from lubricating your engine properly. This may be caused by a clogged oil filter, which can generally be replaced fairly quickly, or the oil itself may have gone bad due to age or contamination.
If switching out your oil and oil filters still does not fix the problem, you may be dealing with blocked or leaking oil injection lines — these can be difficult to repair and replace, so taking the engine for diagnosis by a professional marine engine service is generally the safest bet. Even if the problem is solved, having your engine inspected by one of these services is recommended to ensure no lasting damage was inflicted on your engine while it was running without oil.
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