Water in Oil – How to Prevent & how to fix it.

Water In Oil – An Introduction

Water is a poor lubricant and does not mix readily with oil, leading to inefficient lubrication between mating surfaces. Water also promotes corrosion (rust) within the system. In addition, high temperature environments will boil off at the component contact points, leading to a temporary loss of all lubrication, whilst the impact of these explosions, as the water boils, may lead to pinhole corrosion. Water has the additional property of damaging the oil additives designed to protect the machinery; this is often termed hydrolysis. Water also has the ability to wash out the additives, leaving insufficient to protect the machinery. Finally, water contamination in hydraulic systems or in brakes can boil under these conditions to cause loss of power, uncontrolled hydraulic movement or brakes failure.

Testing for water contamination starts at the point of taking the oil sample. If there is visible water present in the sample, evident by a cloudy or milky appearance or settled to the bottom of the sample bottle, then there is a strong chance of water contamination is present, which will show in the lab report.

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Water In Oil – Prevention

Prevention of water ingress, as all contamination, is usually better than removal.

If the system is free breathing, consider using a desiccant breather to remove water vapour (wet air) before it enters the system. Additionally, when using a desiccant breather the desiccant should be replaced on condition rather than simply time based. So send regular desiccant samples to a laboratory capable of monitoring desiccants to confirm condition.

Any visible fumes or vapours emanating from the machinery may condense onto a cold metal surface. These fumes could potentially indicate the system has water ingress, which should be confirmed by submitting an oil sample.

If the main tank has a drain tap then it is advised to regularly drain small volumes of oil from the system until it runs clear to remove any sludge, sediment and water collecting at the bottom of the tank. Likewise when inspecting the top tank hatch of a system that normally runs hot, and shows signs of water droplets or rust on the top surface, then this suggests water is boiling off from the system and condensing on the cold tank top surface, eventually dripping down into the system again. Note: when inspecting sight glasses any increase in volume may be linked to water ingress.

If the system is using a synthetic polyglycol (PAG) oil, then these products have a natural affinity for water and able to absorb water vapour from the air; such fluids are termed hygroscopic. Consequently, it is important to never half fill an oil sample bottle to send to the lab, but fill to within 10 millimetres of the top. Large air volumes above sensitive samples may give a high erroneous result. However, while water contamination remains undesirable and difficult to remove, polyglycol products can cope with water much better than mineral oil based products.

When examining cellulose based oil filters, a wavy appearance suggests water contamination; in which case it is advised to consult the filter supplier for additional actions how to remove the water.

If using IBCs, drain off any sediment and water from the bottom before drawing from this container and follow the same procedures as above to reduce the likelihood of water ingress. Note: Always store barrels on their side and under a shelter; this keeps an oil surface next to the bung, reducing the likelihood of air circulation and water ingress through natural breathing of the barrels.

Wherever possible, attempt to get equipment up to full operating temperatures as often as possible to help drive off any water. This is a particularly true for large, slow or medium speed marine engines, with cooling systems designed to cope with the engine running at high load. Such systems at low speed tend to over-cool the engine liners. This means water vapour from the combustion processes, condense on the cylinder walls rather than being expelled together with the combustion gases – leading to corrosion of the system (termed cold corrosion).

When submitting samples from systems with additional cooling fluids, such as cooling waters or anti-freeze engine coolants, it is advised to submit a sample of these fluids for analysis. This practice is also useful to (1) rule these out as the source of any contamination and (2) confirm they are in good condition to effectively cool and prevent corrosion in the system

Water In Oil – Removal

The first point to establish when water has been found in the oil – is the ability of the oil to separate from the water. If the oil shows poor water shedding ability then it is unlikely to be easily removed.

Similar to actions to remove dirt ingress the options are to:

a) Change the oil,

b) Filter the oil or

c) Leave the oil.

Changing the lubricant contaminated with water is recommended for small systems, especially if grossly contaminated with water, even if the water easily separates from the oil. This is because the water may have damaged the oil additives and further, most engine formulations emulsify the water, making filtration a difficult and expensive option.

The table below shows the different types of water contamination and their prevention/removal:

Water Contamination Management strategy
Gravity & Drain Coalescing Centrifuge Absorbent Vacuum Dry Breather Active Venting Hot oil filtration / hot oil purifier
Use / Application Remove Removal Removal Removal Removal Prevention Prevent & Remove Remove
Water Type
Gross Free (visible) Yes Yes Yes Yes Yes Yes Yes Yes
Moderate Free (visible) Yes Yes Yes Yes Yes Yes Yes Yes
Emulsion Some Some Some Yes Yes Yes Yes Yes
Dissolved No No No No Yes Yes Yes Yes

Simple methods to remove water such as the “gravity and drain” system, which amounts to regularly allowing the oil to stand for a period, then simply draining off the water – come under prevention. It catches the problem early and prevents subsequent wear.

Systems using hot oil filtration or oil purifiers, then increasing the temperature of the purifier to ~95OC (or maximum your manufacture of the filter and equipment recommends if 95 is too high) to remove the water. Active venting has been classed as both prevention and a removal method as it is used as a removal method to remove water, but once fitted it then turns to a preventative solution for keeping water content low.

If you are using hot oil filtration or oil purifiers, then increasing the temperature of the purifier to ~95OC (or maximum your manufacture of the filter and equipment recommends if 95 is too high) will help remove the water. Active venting has been classed as both prevention and a removal method as it is used as a removal method to remove water, but once fitted it then turns to a preventative solution for keeping water content low.

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