Centrifugal or spinner filters have been around for some time now, initially in niche applications or fitted as an aftermarket accessory. However today, an increasing number of OEMS are installing them as standard fitment on their engines. This is due largely to the impressive filtration capabilities of these systems, and their ability to remove not only wear and external contamination, but also reduce and manage soot levels, and extend oil drain intervals beyond what would have been normally possible.
With the high efficiency of the centrifugal filters lies the problem. The filtration is so effective in removing contamination from the oil that it has rendered routine oil analysis ineffectual to predict the precursors associated with component failure and/or external ingress. Personally, I have seen numerous instances where the oil sample analyses were returning normal results with zero evidence of dirt ingress or increased liner piston ring wear, yet the Filtercake analyses taken at the same time were showing indisputable evidence of dirt contamination and abnormal wear generation. This was further backed up by inspections confirming dust ingress, through corrosion in the airboxes, that due to the location and access had previously gone unnoticed.
However, this doesn’t mean we can stop taking oil samples. Oil analysis is still essential for detecting issues such as coolant and fuel ingress, viscosity and oil degradation. Instead, a three-pronged approach is required: Oil analysis, Filtercake (Ferrogram) analysis and physical inspections/measurements of the cake, to ensure issues are quickly identified and rectified, before they can rob us of potential component life.
Oil sample analysis:
- Fuel dilution
- Coolant ingress
- Water ingress
- Oil degradation
Filter cake analysis – Ferrogram analysis:
- Wear particles
- Wear mechanism
- External ingress (dirt/coal)
- Thickness and/or weight of the cake:
- Too thin/light – centrifuge not operating correctly
- Too thick/heavy – combustion issue and/or high wear generation
Adopting this three part approach to analysing engines fitted with centrifugal filtration will ensure the best possible chance of identifying and rectifying issues previously hidden by the filtration, which has resulted in components not reaching their full potential and life expectancy.