Drawing An Accurate Oil Sample
Professional Skipper Magazine Issue 42 Nov/Dec 2004 (unedited)
Oil analysis, or more importantly 'used oil analysis' what are the benefits? Joining a programme that not only offers accurate results, but also informative interpretations of the figures along with ongoing advice is essential to maintaining your preventative maintenance programme for your equipment.
However, there are certain areas that you the engineer or skipper need to get right before the lab can provide you with those accurate results. As I have said before in the past drawing the sample is a very important part of the process. If the sampling is done incorrectly or is not done the same way each time then it becomes very hard to know whether the results are accurate or even if they are a good representation of the equipment in question.
Thus giving an accurate interpretation of the results becomes difficult. This is because any inconsistencies that show up may in fact be interpreted wrongly.
There are a number of ways samples can be taken to avoid this situation. Two things that should be remembered before taking samples is consistency and cleanliness. Being methodical about the way it is done is a very important part of the process.
The first is the simplest and is more commonly used on vehicles due to access to the bottom of the engine and/or transmission. However, this sampling method may still apply if it's the way you do your oil changes. Once you have warmed up the engine and oil to operating temperature or have just returned from a trip remove the sump plug and drain the oil. Remembering how much oil the sump contains, let about half of it drain out then put the open sample bottle into the steam of oil and take the sample (don't forget to wear your gloves).
Afterwards wipe the outside of the sample bottle and replace the lid. The sample is now ready for labelling and sending off to the lab. One of the main disadvantages of this sample procedure is that it is very hard to do between oil changes. If you need to do this then remember it is very important to keep the way the samples are taken the same.
So when you drain the oil make sure that the container it is going into is very clean so that when you are finished you can pour the oil back into the engine without contaminating it.
The second is done with the use of your hand or mechanical oil evacuation pump, which you would normally use to do your oil changes. Where possible these pumps should not be used, however if they must, then pump a good few litres out first before taking the sample. These pumps can hold a large amount of sediment and/or residue that may not have any relevance to the oil or the equipment. Thus I would suggest, so as too get an accurate set of results that you pump out at lest 5 to 10 litres, depending on the capacity of the sump before you take the sample. Again, if you wish to do this between oil changes then make sure that the oil that you are pumping out goes into a clean container.
Another way, but one that I have used for the last six years is by removing the dipstick and using a small hand-held vacuum pump with a tube and the sample bottle attached to it to draw the oil up. With the right equipment it is one of the easiest and more methodical ways it can be done as the oil is drawn straight into the clean sample bottle.
However, before I attach the actual lab sample bottle I connect an old one to the pump first, draw up the oil until it's full then remove it and attach the lab bottle for the actual sample.
By doing this I am making sure that the line is clear of any dust or dirt and that the sample is a good representation of the equipment in question. The tube that you will need to get down inside most dipsticks holders is ¼ inch or 6 mm white plastic.
To make life easy and to get a good sample cut the tube about a foot longer than your dipstick then melt one end of it and close it off using your thumb and forefinger (I know health and safety ba ba ba, but it is the best way).
Then once you have done this cut a small notch with a Stanley knife about 30 mm up from the end you have just melted and closed. Now some of you may think this is mad, but hey, it takes less than a minute. When you pass the plastic tube down the inside of the dipstick holder you will not only not pick up any of the shit built up in there, but you will also grab a good sample from a midstream position in the sump and not from the sludge on the bottom. Don't forget to attach a new tube to the vacuum pump each time you want to sample a new piece of equipment so as not to cross contaminate the samples.
Using this system oil samples can be drawn at any stage of the oil's life, not just during oil changes. It is also very useful when you are sampling a number of pieces of equipment at different times and in different places as I do in my line of business.
The last is probably the best but not always possible and that is to put in place sample points at which samples can be drawn. This is more suitable for hydraulic systems then engines or transmissions, however if you are able to and your engine/transmission distributor agrees it's possible mount a sample point/valve in the oil return line before the filter.
Then while the engine is running at idle and the oil is flowing open the valve, draw a small amount off to waste then take the sample. As you can imagine if you are taking samples regularly from the same piece of equipment then this would be the easiest way, but hey as I have mentioned it may not always be possible.
A couple of extra notes that will assist with the management of a good used oil analysis programme. Never take a sample from a cold piece of equipment or a container that the oil has been drained into!! Always make sure it is up to operating temperature before the sample is taken and where possible always take it straight after you have shut the equipment down. This way the oil will be well stirred up and the samples are good cross representation of the equipment in question.
Also the lab labels are a very important part of the process. On the label you will be asked for a number of pieces of information. This normally includes a contact name, equipment ID, description/vessel name, make and model, sample date, oil type/grade, equipment and oil hours, as well as any top-up oil used.
You should complete the label as fully as possible as all this information is very important, not only for tracking of the sample, but also for correlating the results against your records. If you need further assistance with this or would like to enter a fully managed programme please don't hesitate to contact me. Good sailing and oil sampling to you all.
Written By Kelvin Hieatt
Managing Director Marine Diagnostics Ltd
