One day a v6 engine came into the component shop for a rebuild after water was found in the oil and due to the age of the engine, it was decided that the best course of action was to perform a full rebuild.
The source of the coolant leak became evident as soon as we lifted the induction manifold, coolant had been leaking from both head gaskets into the vee of the block. The camshaft on this engine ran in the vee and would have been exposed to the incoming coolant water.
When the camshaft was removed/cleaned; pitting was evident on all the cam lobes in a triangle pattern with the severest pitting on the high load area of the cam! This was my introduction to the damaging effect water ‘flashing’ on a loaded surface and was stark evidence of how damaging this can be.
Water has multiple damaging effects on lubricating oil:
- Corrosion (rust)
- Biological activity
- Flash (explosive steam formation)
- Additive loss
Corrosion is the most familiar effect water has on ferrous surfaces. Iron + Water + Oxygen = rust. Rust damages the corroding surfaces and rust particles are hard enough to damage other surfaces and thereby spread the damaging effects system wide.
Free water present in the oil can allow biological activity. Bacterial corrosion is seriously damaging to surfaces and can be difficult to stop once it gets going. Sulphur reducing bacteria are particularly damaging to metal.
Flashing, or explosive steam formation under loaded conditions is a frequent cause of bearing damage. In its simplest form water droplets are heated to the point they boil into steam and ‘flash’ oil off the bearing surface. The process is similar to how steam cleaners remove oil from surfaces. The loss of oil film results in adhesive wear until the oil film reestablishes itself. Under high load conditions, water droplets flash into steam explosively damaging the surface under the droplet. This is what had been responsible for my pitted camshaft.
Water creates issues with oil additives in two ways. One, some additives are soluble in water. When water is present, additives are ‘dissolved’ into the water and may no longer function in the same way they did when in the oil. Also, if the water is removed from the oil, the additive will be lost to the system. Two, oil additives are normally ‘active’ in chemical sense waiting for an opportunity to do their work. When these additives encounter water, they can react with the water rendering them inactive and will therefore be unavailable to perform their normal function.
How much is too much water?
There is no simple answer to this question, a lightly loaded system that uses an oil with little to no additives may tolerate up to 0.5% water with no ill affects. While another system that has higher loads/temperatures/oil-additives will be adversely affected with as little as 0.1% water or lower.
As dry as possible is the best approach to dealing with lubricating oil water contamination, if we can keep water at or below 50ppm by mass, then we are unlikely to see any adverse effects on the equipment.
If due to environmental or other factors we cannot keep the oil this dry, then a decision will need to be made as to what will be an acceptable amount of water before action is required. Always ask the equipment manufacturer as the first step in answering this question. If they cannot provide an answer, then trials may need to be run to establish water limits.
As a general rule avoid free water if at all possible, if free water is detected in the oil steps should be taken to remove it from the system.
If due to the nature of the work been done, or due to the environment the equipment is working in, water ingress cannot be avoided, then methods will have to be deployed to remove the water from the system.
There are five main ways this is done
- Water Drain off.
- Absorption filters.
- Centrifugal ’Spinner’ purifiers.
- Coalescing Systems.
- Evaporation water separators.
If the system uses a low additized oil and there is opportunity for water to settle out of the oil in a holding tank, then draining off the water at regular intervals is one approach to remove free water.
Absorption filters are made of water absorbing cellulose media and is effective at removing relatively small amounts of water from the system. In many cases this may be all that is required to keep light water contamination in control.
Centrifugal (spinner) purifiers are recommended for higher water loads. They come in a wide range of sizes and can be scaled to the amount of water that needs to be removed from the system. However, they can struggle to remove emulsified and dissolved water from the oil.
Coalescing Systems use mechanical or electrostatic means to coalesce water from the lubricating oil. Like centrifugal purifiers, coalescing system can remove large amounts of water provided the water is not bonded/emulsified to the oil.
Evaporation Water Separators are used if the oil needs to be kept very dry and these can remove emulsified and dissolved water from the system. There is a range of evaporation water separators available and work best on systems with limited water contamination. One potential issue with evaporation water separators is that the combination of heat and air exposure can result in the oil becoming oxidized in the process and thereby shortening oil life.
For further information or to establish a proactive testing program for your oil, coolant, or fuel in critical operating equipment feel free to contact ALS Tribology laboratory or any of our regional testing labs.
David Doyle, CLS, OMA I, OMA II
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