Where Should You Take an Oil Sample From?

A few weeks ago, I got a question about the best place to take an oil sample for oil analysis. Instead of generic answers like “after the pump before the filter” or “never on the drain,” I like to take a more practical approach.

What Do I Consider?

• Criticality: If the component is critical, then I will want to ensure the sample I take is the best one possible and that may include spending some money for an oil sample fitting and for installation of said fitting. I will also want to consider sampling more frequently, as it’s important to trend.
• Size of Reservoir: I’ve been asked before about taking samples from small components with reservoirs less than a few liters. In general, I recommend not taking a sample from a small system unless you’re sampling while you change the oil (usually annually). Be careful sampling small reservoirs because, with flushing and the sample, you may need to top up after sampling (hence why I recommend doing it only when changing oil). Note: criticality is still the number 1 priority here.
• Pre-Existing Options: What’s available on the component already that can be modified? I look for plugs, drains, bullseye fittings, breather ports, sight glasses and fill ports. These can all be modified to install a proper sample fitting or you can simply install a ball valve tap.
• Accessibility/Repeatability/Simplicity: As with most PdM technologies, repeatability is extremely important in diagnosing problems. Oil analysis is the same. I always ensure that my sample location is easily accessible and safe to sample. I want the sample to be taken the same way each time. The easier it is to do it right, the higher the probability that it will be done right.

I hope this helps you with picking sample locations, and if you’re looking for some help in this area, email me a picture and answer those 4 bullet points and I’ll happily give you my thoughts.

Reliability Never Sleeps