Changing Oil Types – Mixing Wrong Oils – Intro
At some point all lubricated systems require an oil change either because the oil has come to the end of its useful life or has become contaminated. When performing oil changes – suppliers and product types may change – as business decisions are made as to which lubricants to use, based on performance testing and cost of the lubricant.
Therefore, throughout the life of the machine it is possible that several different brands of products have been used. Equally, in large oil filled systems performing an oil change may cost thousands of pounds, hence the decision is often made to use the new lubricant supply as top-up until the previous oil has effectively been removed. This means mixing of two products – often the source of many problems. The oil thereafter is never actually the new or old product and room for reasons the problem lies with the “other” oil. This approach is ok to have, as long as the individuals making the decision to mix the oils have fully researched the compatibility of the two oils and not only with the latest product
Changing Oils – Is an oil change really needed?
The first thing to establish when changing oil is the reason for the change.
If it is just time based then this may be wasteful exercise, as oil should only be changed based on condition, unless the oil change is part of the warranty of the machine manufacturer.
If the volume of the oil makes the oil change an expensive exercise or indeed if downtime is not currently convenient, it is best to ensure any oil report recommendation to change the oil, has been confirmed by a second sample report. Please note an oil report is based on the sample received and problems such as incorrect submission information, sampling when the machine was not at operating temperature, drawing from the bottom of a storage tank or dirt entering the sample bottle when sampling etc. – a second sample is much cheaper than an unnecessary oil change. It is also worth establishing if, contamination is the problem it can be removed by other methods such as filtration or draining bottoms of tanks etc., which may be prove to be a far more suitable alternative.
If changing the oil is based on a fluid condition alone, such as poor water separation properties, which prevents simple settling of water and draining, or poor anti-rusting characteristics indicate loss of anti-rust protection – risking corrosion wear if water entered the system, then it may be worth introducing a stricter monitoring programme. This can help extend life of the oil, allowing an oil change to take place at a more convenient time, possible during an annual shutdown period and promote corrective procedures to reduce water ingress such as employing desiccant breathers etc. Finally, it is worth establishing if the oil change is just masking an underlining problem, such as a fuel or coolant leak, which should be addressed asap.
Changing Oils – Using compatible oils
When changing products that are compatible, it is worth noting switching from a group 1 to a group 3 product; does not mean a 50% change of oil will give properties of the mix half way between those of the two products. This is also true when simply partially changing the same oil for fresh oil. The facts suggest the oil mixture will default to the worst scenario, so if the current product lasts 6 weeks and the new oil lasts 1 year, the properties and life of the oil mixture will be much closer to 6 weeks than the half way point between the two predicted remaining life. This is because the relationship between top-up and life of the oil is not linear; oxidation promotes more oxidation. Hence it is worth considering the benefits of the short term lower expenditure against an overall larger spend at that time. Insomuch much of the value and useful life of the new oil added will be lost, as a total oil change will soon be necessary. Note this cost comparison assumes the only factor at work is oxidation and the machinery conditions are identical in both scenarios.
Changing Oils – Using incompatible oils
When changing oils that are known to be incompatible, it is always worth discussing with the lubricant manufacturer how clean the oil change must be, as there is always the risk some of the previous lubricant remaining. The steps to achieve this level of cleanliness should always be costed before making the final decision to switch to a lubricant that is not compatible with the current lubricants in use.
The practicalities should also be considered such as does this mean all systems will be changed at once, or will some systems be running on one type of oil and some run on different oil? If all is to be changes at once, then this could be a large demand on resources and so needs careful planning. For example you may need to decide the cost of disposing of the unused barrels of the old product.
Equally if the plan is to phase in the lubricant switchover, then steps to prevent cross contamination e.g. separate oil fill containers, storage, labelling, sampling equipment etc. Training must be paramount. The team must know what oil should go in which machine, even despite these preventative measures there is nothing to stop human error leading to cross contamination of the products. See example picture on the left where the customer had separate warehouses for the two oil types, believing they had designed a system that was impossible to cross contaminate the products, yet they still managed to mix a mineral and synthetic product in quite considerable quantities.
The process of making the change is not just simply draining one oil and replacing with the new one in applications like this, but requires repeat flushing to remove the contaminating fluid. There are several options and there is no universal best option for making changes such as this, but your OEM or lube oil supplier should be able to assist in picking the most practical and cost effective option.
Drain as much out as you can and then fill with the new oil – This is by far the cheapest option adopted by many operators, but often leads to scenarios in the above picture. This is an approach that should not be adopted if the oils are incompatible, however, the cost of solvent/flushing oils often make cost conscious engineers tempted by this option.
Use a solvent or flushing oil (usually a lower viscosity version of the current product or an OEM approved cleaning solution) to remove the majority of the old oil and hence make removing the old oil easier when introducing the new product. These solvents can often be quite expensive, so it is often worth asking the lube oil supplier to include in the quotation for switching to their new product an additional line on the quotation to include the costs of flushing liquids.
Flush with the new product – This approach uses cleaning out the empty system with the new product to remove traces of the old product, draining and refilling again. Again, it is worth costing this exercise before making the decision to switch.
Solvent/flushing oil followed by flush with new product – This gives a very thorough cleaning of the system, but is the most expensive option. Hence the importance of establishing the degree to which the oils can be mixed without causing problems by checking with your oil supplier. The cleaner the requirements, the more heavily flushed the system will require. As a very general rule of thumb, 90% can be removed with 1 flush, 99% with 2 flushes and 3 flushes removes up to 99.9% in perfect conditions.
Changing Incompatible Oils – Check seal compatibilities
Before the final decision is made to switch lubricant types it is advisable to ask the laboratory and/or oil supplier to carry out a seal compatibility test to check the impact of the new oil on the machine seals i.e. a seal swell test. If expecting at the end a 1.5% mix of the old product in the new product and the operating temperature is 45OC the lab can simulate these conditions and create these mixes to establish if the seals are likely to change as result. Ideally an unused spare seal material should be submitted as part of the testing to confirm compatibility.
A picture is below of material from seal damaged by incompatible oil.