Condition based oil change is a type of predictive or proactive oil change that is performed for the right reason and at the right time. The other types of oil changes are reactive oil changes and preventive oil changes. In the old days, when oil analysis was carried out in most large facilities, guidelines were set by the original equipment manufacturer (OEM) and the OEMs usually erred on the safe side while recommending oil change frequencies. As much as 50% of the lubricant’s useful life was wasted due to this error. The lubricant was changed even sooner in some cases when a warranty was involved. Maintaining the warranty, required the lubricant to be changed at specific time intervals, but today most OEMs recognize a good oil analysis program and allow the warranty to continue with extended oil drain intervals. Obviously, this has to be discussed and agreed upon by the OEM before establishing the new schedule. Condition based oil changes are risky. They can help you avoid a lot of costs but they can also result in catastrophic failures if not done correctly. You need an expert for your oil analysis program for executing condition based oil changes. Extended drain intervals are not suitable for all kinds of equipment. A deep understanding of - the equipment, its operating parameters and its material makeup is very important. Make sure to incorporate proper oil sampling techniques and get all the valuable information by performing relevant tests before making any decisions. If you have a large reservoir, your potential savings will be greater as compared to a smaller reservoir because of the volume of oil involved. But you can still take advantage of information gathered from the analysis of a smaller reservoir as they are more critical. Apart from the size of the tank and volume of the oil, other factors to consider are - operating temperatures, quality of filtration, the amount of makeup oil and breather systems. Additionally, you need to have a deep understanding of the strengths and weaknesses of different oil analysis tests and how they are performed. Discuss all your concerns with your oil analysis laboratory to know about additional special tests that can be performed to obtain all the information that can help you make better oil change decisions.
Limitations of tests for Oil Analysis
Oil Analysis tests can sometimes be unreliable. Let’s take an example of a spectroscopic analysis to understand it better. Depending on the analysis method and particle composition, it can only detect particles smaller than 7 microns. This means that your analysis report will show you a concentration of 100 parts per million even when there are visible metal particles in the sample. There are alternate methods to obtain information about your lubricant’s condition like microwave digestion. This method breaks down larger particles to obtain a complete spectral burn and identifies the particles in the oil. Another great method to identify and characterize large metal particles is through Analytical ferrography. It can also identify sizes, shapes and morphology of the particles apart from their quantities. This can help you determine and understand the type of wear occurring. It is also important to beware of false positives in your oil analysis report. For example, if you have a high copper concentration in your oil, then it may not be actual wear; it might be because of Zinc dialkyldithiophosphate (ZDDP) - an additive that can cause copper leaching from the cooler. Another common false positive is Silicon. If you see a sudden and drastic increase of silicon in your oil, it can be from a recent repair job. Some repair jobs in your machinery use silicone sealer or room-temperature vulcanizing (RTV) silicone. If your analysis shows the presence of water in your sample, it may be misleading too. Crackle tests or Fourier transform infrared spectroscopy are performed by most labs to detect water. Both these tests are approximate; if you want to know the exact amount of water in your sample, perform a Karl Fischer titration. Note that you will need to specify the drying method or the evaporator to get a proper reading. Particle Counts
There are certain special tests which should be performed to gain additional information even after having extensive oil analysis tests for extending oil drains. Oxidation test - A rotating pressure vessel oxidation test (RPVOT) compares oxidation stability of the new lubricant and the in-service lubricant. Ruler test – The remaining useful life of the in-service lubricant as compared to the new oil can be estimated using this test. Demulsibility test – This test shows a lubricant’s ability to shed water. Copper strip corrosion tests – These tests help identify the remaining anti-corrosive additives present inside a lubricant. Other tests like the varnish potential rating, quantitative spectro analysis and membrane patch colorimetry (MPC) can help identify depleted additives and amount of oil degradation byproducts. These were just a few of the special tests that can help you in making better decisions about your oil drain intervals. Always remember to communicate with your lab to ensure that you have all the information you need for making this decision that can avoid costs and prevent from catastrophic failures.
This information is provided for guidance and informational purposes only. This website and information are not intended to provide investment, laboratory or manufacturing process advice. The information contained herein has been compiled from sources deemed reliable and it is accurate to the best of our knowledge and belief. However, Castrol cannot guarantee its accuracy, completeness, and validity and cannot be held liable for any errors or omissions, as the results change depending on the working condition/environment. Changes are periodically made to this information and may be made at any time. All information contained herein should be independently verified and confirmed.