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Engine Oil Contaminated With Diesel Fuel Or Water


On occasions there can be an unexplained increase in the tractor engine oil level. The question is why has this happened.

There can be one of two contaminants in the oil; either coolant water or diesel fuel can escape from their systems.

The first observation to make is to assess the colour and consistency of the fluid. White creamy coloured oil is indicative of water contamination, where as diesel contamination tends to dilute the oil making it less viscous. Contamination of the oil must be remedied immediately as it will cause damage to the engine.

Fuel Contamination

There are three possible routes for fuel to enter the lubrication system

  1. Fuel lift pump – The diaphragm can split providing a route for diesel to enter the engine crank case.
  2. Injector pump – Injector pump shaft seals have been known to fail.
  3. Damaged Injectors – Leaking injector nozzles during periods of inactivity can drip their contents into the cylinder which then runs down between the piston and bore into the sump.

Water Contamination

Water can enter the oil system by:-

  1. Leaking head gasket – This allows contamination between the sections of the engine. The most likely cause of a leaking head gasket is from over heating.
  2. Cracks in the cylinder head or block – From overheating or frost damage.
  3. Failure of seal around bottom of wet liner – Incorrect coolant mixture. For example, John Deere coolant systems should be filled with CoolGuard.
  4. Corrosion of wet liner / porous block – Coolant without corrosion inhibitors added increases sludge formation, which is not only corrosive but also abrasive. This can eventually pierce the cylinder wall.
  5. Heat exchanger failure – Many engines are fitted with water to oil heat exchangers which can leak fluids between the systems. This can also cause oil to enter the coolant system.
  6. Exhaust pipe – Uncovered vertical exhaust pipes on tractors that have been left outside in the rain will eventually fill up with water (a scenario all too common with old tractors left to decay in farm yards). As the water level increases over a period of time it will find a path into the cylinders (through the exhaust valves) and the engine. On 4 cylinder (and more) engines, there is always at least one exhaust valve open at any one time.
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2 Responses to “Engine Oil Contaminated With Diesel Fuel Or Water”

  1. Hi Great Site, lots of info. I have a different problem with our 4 cyl 35, the water flows out from the drain at the top of the radiator.

    Any ideas.


  2. I have a problem with diesel oil contaminating the engine oil in my Dexta. This happens via the intake manifold. After the primer is used to coat the heater coil with diesel the diesel continues to flow very slowly into the manifold and eventually makes its way to the engine lubricant. This is a very expensive fault which would eventually damage the engine if the oil is not replaced. I would appreciate hearing from anyone else who has encountered this problem. I have fitted an on/off tap to the heater coil feed but a moment of forgetfulness ( to which I am very prone) and the engine oil has to be replaced.

    • Vincent Braniff
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