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fuel in bilge

I appear to be getting some fuel in my bilge water. What might be wrong?

Asked by: Celeste  | 7.23pm, Wednesday 16 October

WW says:

The following assumes an inboard diesel engine. The most likely reasons are leaks from joints in the fuel pipe work or from a fuel filter. If the engine is running normally, then the leak is more likely downstream of the injectors... Such as the fuel spill-off pipes, or the return to the fuel tank. If there is a leak before the fuel pump, this will often allow air into the system, which causes erratic running.
If you trace the fuel lines from the fuel tank to the engine filter, then to the lift pump, and on to the injectors, and back to the return lines, you should be able to trace any leaks. Wiping clean (and ensuring the lines are dry) with kitchen paper should allow you to spot any leaks when the engine is running.
Be aware that if there is a leak on the high pressure side of the fuel system, the diesel come out with such force that it can penetrate the skin, so take care.
You should also check the fuel filters for leaks as well, and pay particular attention to any shut off valves and flexible hoses in the system.
It may not be fuel in the bilge water, but other oils. Some engines, particularly older ones, do have a tendency to leak lubricating oil from the dipstick, breather pipes, sump drain plugs/pumps. fillers and filters, as well as the rocker box cover sometimes. Although some are easy to spot, others can be more difficult. Giving the engine a very good clean with a suitable engine degreaser (and not allowing the residues from cleaning to be pumped overboard) then allows you to spot any leaks.
The engine sump should sit above an oil tight tray, which the bilge put should not empty from. Then if any oil or fuel leaks out, it can be captured and moved safely, without causing a pollution incident. Ensuring that any bilge water levels are below the oil-tight tray are very important. If the tray is kept dry, an oil-absorbent pad can be placed under the engine, which as well as reducing contamination, can help trace any oil leaks (or fuel leaks)
Fuel oil may also leak from tanks, either from the train point or damage/corrosion to the tank itself- again, good cleaning of the compartment can help trace any leaks.
Some stern glands that use grease in a conventional stuffing box can also lead to apparent oil in the bilge water, but usually only if they are packed with the wrong type of grease.
If you have an inboard petrol engine and have fuel in the bilge, I would strongly suggest you have a marine engineer take a look very quickly, as spillages of petrol into a boats bilge will form explosive mixtures, with potentially disastrous consequences.
If you are having problems with oil in bilge water, draining the Lille and cleaning it can be very helpful. Using oil absorbent pads, which float on the bilge water and only absorb hydrocarbons (fuel, lubricating oil, etc.) can be useful to mop up any unforeseen spillages. You can also fit a filter into the bilge pump hose which scrubs any contamination out before discharge overboard.

Mark Langley  | 10.39AM, Thursday 17 October

For Lille, I meant bilge! Sorry, autocorrect on a iPad...!

Mark Langley  | 11.54AM, Thursday 17 October

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