~Taking a Proper Engine Oil Sample for Analysis

PATH: REFITTING & REPAIR » DIY » Propulsion » Engines » Lubrication » Oil » Analysis »

^ Sampling an engine that cannot be run and warmed up
^ Sampling with a Sampling Probe
^ Sampling by Vacuum Extraction
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It is always best to take the oil sample from a warmed up engine, so the oil is thoroughly mixed and everything in the oil, especially contaminants, are evenly “in suspension”.

In the event that the engine cannot be run for some reason, then the entire oil sump must be drained into a perfectly clean container and the entire container of used oil will have to be processed so the sample will be more representative (usually at an additional cost to stir up the contents and draw the sample), but unfortunately, far too often the analysis readings will be skewed enough to be misleading. Yet, this may prove useful in determining if a serious problem exists such as fuel dilution of the oil due to a leaky injector or fuel pump, or coolant contamination from a “blown” head gasket. Go to Engine Oil Analysis for a full interpretation of oil analysis results.

0606st_oil_change_03_z_oil_drainedThis oil was undoubtedly contaminated by the oil filter!

Taking samples from either the drain stream, the waste oil container, or the used filter is the least desirable method of obtaining an engine oil sample, as doing so more often then not results in an unrepresentative sample. The used oil filter usually contains high concentrations of contaminants that will throw off the analysis. The waste oil container may already be contaminated or it can easily become contaminated by falling debris. Then there is the sampling of the drain stream. In the early days of oil analysis, it was believed that a good sample could be “caught mid-stream” as the oil was draining from the oil sump (on most engines the oil pan acts as the sump). The sample was caught, not at the beginning of the draining and not near the end, but mid-way between (mid-stream, like at the doctors office). It was quickly realized however that a sample from the drain stream often contained high concentrations of contaminants from the bottom of the sump and the drain plug hole surroundings, (e.g. metal from the threads, etc), so better methods of taking a sample had to be developed.

Oil Sampling Probe

The most preferred method of taking an engine oil sample is with an oil sampling probe. If the engine is not equipped with an oil sampling probe valve, one can usually be installed. The valve is available from most large engine dealers. The probe valve allows a probe to be inserted while the engine is running, and the engine’s own oil pump will pump oil through the probe into the sample bottle. Just remember to reinstall the probe valve cap to keep the valve clean for the next sampling.

This sampling method requires a Brass Probe (like a Cat # 8T9208) and approximately 15 cm (6 in) of tubing (like Cat # 6K0713 or 5P6442 bulk cut to length). Some sample kits may already come with a disposable probe and tubing.

The process of taking an oil sample by an oil sampling probe is as follows:

1 – After the engine you are going to sample has been started and has been running long enough for the engine to warm up. set the engine at low idle and remove the dust cap from the oil sampling probe valve on the engine.


2 – Insert the probe into the valve and collect about 100 ml (4 fl oz) of oil into a small waste container. This will clean the valve and helps ensure a representative sample. Dispose of the waste oil properly. If the oil flow is slow at low idle, it may be necessary to have someone accelerate the engine to a higher idle while clearing the valve and extracting the sample.


3 – Insert the probe into the valve again and this time fill the sample bottle to the proper level (usually one-half to three-quarters full). Do not fill to the top. Do not allow any dirt to enter the bottle or contaminate the inside of the bottle’s cap.


4 – Withdraw the probe from the valve and secure the sample bottle cap tightly. otherwise, it can make a real mess inside the shipping cylinder. Make sure that the sample bottle’s outside is clean and place the bottle with the completed label into the shipping cylinder.


5 – Don’t forget to reinstall the probe valve dust cap.


From MacAllister Machinery

Vacuum Extraction

Vacuum Extraction is the most recommended method of taking an oil sample if the engine is not equipped with an oil sampling probe valve. With vacuum extraction, a length of clean plastic tubing is inserted into the oil sump (usually down the dipstick hole) about half way into the oil and the oil is drawn up the tube into the sample bottle by the vacuum created in the bottle by a hand operated vacuum pump. The equipment needed include the vacuum pump, a sample bottle, a length of sterile extraction tubing, and a clean tubing cutter. These items are readily available from many sources including most engine dealers, engine service shops, and oil analysis laboratories. Some engines (like Hino 4 & 6 cylinder diesels) require a smaller (3/16″ O.D.) diameter tubing to fit into their smaller I.D. dipstick tube. This smaller tubing is often stocked at local hardware stores or can be ordered. The hand vacuum pump’s knurled tubing sealing nut usually has no problem compressing the tubing sealing “O” ring enough to seal the smaller diameter tubing into the vacuum pump. Always store the vacuum pump, the clean new extraction tubing, and the tubing cutter, each in a clean place such as in heavy clean Zip-Lock type storage/freezer bags.

NOTE: You may want to wear mechanics gloves or surgical gloves (as shown below) to protect your hands and facilitate cleanup afterwards.

The process of taking an oil sample by Vacuum Extraction is as follows:

1 – Ensure that the engine has been properly warmed up, so the oil is thoroughly mixed and everything in the oil, especially contaminants, are “in suspension”.

2 – Cut about a half-inch of tubing off the loose end of the new tubing roll with a clean cutter to rid the tubing of any contamination that may have drifted inside the end. The roll of sterile extraction tubing should be stored in a clean Zip-Lock type bag until needed.

3 – Mark the new tubing to the length of the dipstick (tip to seal). This mark will be used later when inserting the tubing through the engine’s dipstick hole into the engine’s oil sump to reach the proper depth in the oil.

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4 – From this mark add enough tubing to reach the …
5 – Insert the tubing into the …
6 – Remove the lid from the …
7 – Insert the extraction tubing into the …
8 – Hold the pump upright and slowly …
9 – It is usually …
10 – Unscrew the …
11 – Withdraw the used …
12 – Store the …
A Note: You may wish to …
Another Note: Wearing clean …
An Important Note: If the pump requires internal cleaning,…
A Very Important Note: Never use the same vacuum pump for extracting …
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