Boat Engines Operating in Oil-Contaminated Water

Jun 18, 2010

Boat Engines Operating in Oil-Contaminated Water

In light of the current oil spill in the Gulf of Mexico, Mercury Marine has prepared the following observations and recommendations regarding the operation of marine propulsion engines when oil-contamination is present.

Additionally, to assist Mercury dealers who are servicing boats in affected areas, Mercury is taking orders for relevant service parts that will receive 180-day terms and can be returned within that period with no restocking fees. The order must be approved by the dealer’s Regional Business Director.  Dealers should contact their Mercury representative for more details.



Marine propulsion products operating in oil-contaminated water face a number of variables difficult to predict. Operating conditions could range from a light oil slick on the water surface in offshore use to a crude oil layer several inches thick mixed with oil dispersants and water in near shore areas. The water may consist of any combination of saltwater, brackish or fresh water. Although the potential chemistry is largely undefined, there are a number of considerations when operating outboard, sterndrive or inboard products in such conditions. 

1) Cooling system:

  • Small cooling passages can become blocked by oil sludge.
  • Thermostats and poppet valves can become plugged by oil sludge.
  • Water strainers and outboard telltale ports can become clogged.
  • Water pump efficiencies can be reduced by the fluid mix.
  • Coated cooling systems can become inefficient, resulting in higher engine block     temperatures.
    • Because sensors monitor the cooling-water temperature rather than the engine block temperature, alert systems for some products may not effectively protect the engine block from high temperatures.

2) Degradation of rubber-based components:

  • Water pump impellers may absorb oil and swell.
  • Debonding of rubber from solid backing materials can occur.
  • Hoses, engine mounts and other rubber-based components may suffer from swelling, loss of rigidity, decrease in strength and possible failure.
  • Bellows used on sterndrive products (U-joint, exhaust and shift shaft) are of special concern due to their function in sealing the boat transom.

Corrective Actions:

If possible, avoid operating marine propulsion products in oil-contaminated waters for extended periods of time. If a vessel is used in oil-contaminated waters, monitor engine operating temperatures.  Immediately after use the cooling system should be flushed with hot water, not to exceed 65° C (150° F) for 10 to 15 minutes. 

  • Outboard, sterndrive and inboard products equipped with a fresh-water flushing system are to be flushed with the engine NOT running.
  • Sterndrive and inboard products NOT equipped with a fresh-water flushing system must be running to flush the cooling system. Observe the engine operating temperature and do not allow the engine to overheat when flushing.

Extended exposure to oil contaminants may not have an immediate effect on engine components, but exposed units should be scheduled for frequent inspection of all rubber-based components. Those components should be replaced at any sign of degradation.

Exterior surfaces should be cleaned as needed to control buildup of contaminants and to keep water inlets unobstructed. A power washer set to an appropriate pressure and spray pattern may be used on painted surfaces and anodes. Anodes may also be removed and grit blasted, if necessary. However, do not use a power washer to clean soft surfaces such as bellows, hoses and seals due to possible damage. Instead, use a water hose at normal pressures.

Consider environmental impact when choosing cleaning chemicals. Disposal of parts, cleaning materials and chemicals must comply with local regulations and guidelines.

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