4 Diesel Oil Pollutants Lethal to Your Engine

September 20, 2016 - 9:00 AM by Samantha Pudney


Lethal Oil Pollutants

Have you ever suffered from a sudden engine failure? Chances are it didn’t just happen out of nowhere. Oil pollutants can cause serious engine damage or instant engine failure if not monitored and treated early. Oil degradation is one of the leading causes for that inconvenient, unexpected stop in your marine engine.

While some contaminants can be treated with a simple oil change, others are a clear sign of an actively failed condition that requires a more complex solution. Fuel dilution and glycol contamination, for example, can’t be fixed by changing the oil or even trading up to a better quality lubricant.

Each year, hundreds of marine engines falter due to the presence of glycol, fuel, soot and water in the engine oil. To avoid joining the lethal oil pollutants statistic, be proactive in the detection of contamination in your own vessel.


A defective seal or cracked cylinder head offers an easy passage for glycol to enter your engine oil. The risks associated with contamination in this instance are heightened and can result in a wear rate up to ten times greater than water contamination alone. Other problems you could face include:

  • Sludge, deposits and oil flow restrictions due to filter blockage, it doesn’t take much for glycol to transform your marine engine oil consistency.
  • Precipitation as a result of reactive oil additives, leading to the additional loss of antiwear and antioxidant performance.
  • A fast and significant drop in the oil alkalinity (the base number) to incur an unprotected corrosive environment in your engine.
  • Impaired lubrication and oil cooling due to increases in oil velocity.

Fuel Dilution

If you frequently start your engine in a cold operating environment this can create fuel dilution problems down the track. Severe dilution is a direct association with leakage, fuel injector issues and weakened combustion efficiency, none of which are easily rectified with an oil change. Here are some of the most complex risks associated:

  • Waxing, comprising of low oil pressure and starvation, is created because of cold conditions.
  • Damaging deposits due to thickening motor oil and a premature loss of base numbers, including engine protection.
  • Collapsing oil film thickness and premature combustion will wear down the piston, liner and rings, due to low viscosity.
  • Accelerated wear around the combustion chamber as a result of fuel dilution causing a wash-down on the cylinder liners.



As a normally-occurring byproduct of combustion, soot exists in most (if not all) in-serviced diesel marine engines. It can reach the engine by any number of methods, most commonly during engine operation. The presence of soot is relatively normal for boats that have seen a lot of time out on the water, so don’t panic just yet. However, if the intensity and condition of the soot appear to be abnormal, then here are some of the associated risks:

  • A high soot load can be incurred as a result of poor ignition timing and a restricted air filter, which can’t be reversed by an oil change.
  • Increased sensitivity to abrasive wear such as soot is an associated problem with many new diesel engines, which are designed to produce lower emissions and higher injection pressures. This can also lead to a rocker arm seizure.
  • Interference with combustion efficiency and poor fuel economy.


First-time boaters can often believe that water is the lesser evil in engine contamination, but in actual fact, the element is one of the most destructive of all pollutants. Water attacks additives aggressively, introducing base oil oxidation and interfering with oil film production. While lower levels are perfectly normal, a high level of water should ring alarm bells:

  • Attacks on the surface and oxidation of the oil as a direct result of water condensation in the crankcase.
  • Build-ups of sludge due to water soaking up additives, soot, oxidation products will knock out filters and restrict flow to essential components of your engine.
  • The potential for the severe corrosion of common acids is starkly increased by water.

In order to avoid these risks in your own boat engine, practice proactive maintenance and oil analysis to stop the problem at the root. Counteract the associated risks by taking the extra time to understand each component of your boat’s engine and the care required for smooth sailing.

Best practice is to assess the state of your engine regularly to protect against the accumulation of oil pollutants, especially if it is being placed into storage. This routine will keep you and your passengers safe and add months, if not years, to the lifespan of your boat.

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