Wouldn’t it be great to look at your dashboard and know at a glance when it’s time to change your oil? Some car manufacturers currently offer this option. However these approaches often rely on software algorithms that use data like average speed, rpm and mileage to estimate the oil’s health. Cambridge Applied Systems, in conjunction with several engine manufacturers, recently began testing a dedicated on-board sensor that measures oil viscosity in real-time, allowing condition-based oil health monitoring.

The system is based on Cambridge Applied Systems’ SPL571 viscometer, the latest in a line of viscometers that Cambridge makes for laboratory and process use. According to Cambridge, due to its compact and rugged design, the SPL571 is an ideal tool for on-board viscosity measurements in engine applications and is currently used in a number of major equipment OEMs, including;

  • A locomotive/marine engine manufacturer,
  • Several engine and lubricant manufacturers,
  • Compressor manufacturers around the world,
  • OEM used oil analysis system manufacturers,
  • A European car manufacturer and
  • A wide variety of labs engaged in blending and two-phase system research.

The SPC571 miniature viscometer provides users with a window into the complex interactions of machine and lubricant in real-time, providing a way to monitor and even predict changes in oil chemistry, based on real data, under real operating conditions.

In fact, one SPL571 user has reported an 83 percent reduction in new model development and testing times, from three years to six months based on real-time viscosity data from various loading conditions. With real-time viscosity data, a typical 2,000-hour bench test can now be performed in as little as 300 hours.

The true value of real-time data trending is that it provides a window into the transient stresses on a lubricating system as a machine undergoes various operating and duty cycles. These complex changes taking place inside an engine or compressor often cannot be determined from a routine oil sample because the data represented by such a sample simply reflects a snapshot of the oil’s condition at the time the sample is taken. However, with real-time oil analysis, transient changes due to fuel combustion or refrigerant interaction, as loading and environmental conditions change, can be captured, allowing oil viscosity data to be evaluated throughout its operational life span.

On-board Engine Monitoring System
On-board vehicle diagnostic systems are becoming more sophisticated. However, the basic oil change recommendations provided by engine manufacturers have little to do with actual driving conditions or vehicle conditions and are usually fairly conservative to allow for the worst-case scenario. As such, millions of gallons of oil are needlessly changed each year due to premature oil changes. Conversely, engine damage may occur due to significant viscosity changes, which would go unnoticed simply by changing oil at a predefined OEM recommended interval. To resolve some of these issues, several major automakers have publicly announced plans to include more sophisticated on-board sensors, and hope to include oil health as a key performance parameter.

Engine designs have changed significantly in the last several years. EPA-mandated fuel changes have significantly altered exhaust and blow-by components in engines, while Exhaust Gas Recirculation (EGR) has changed the operational performance characteristics with newer engine designs deploying this technology.

With real-time viscosity monitoring, the effects of engine design on the oil’s viscosity can be measured directly, providing more data to engine designers and lubricant manufacturers. Due to its comparatively small size (the SPC571 is typically installed with a ½-inch threaded fitting and has less than a 1-inch profile) this viscometer fits easily into most engines. A larger version of the viscometer that can be plumbed with ¼-inch tubing to accept lubricating oil directly from the engine is also available for use in larger engines where remote mounting is preferred.

The instrument is used in steady-state engine tests as well as performance cycling tests. Because of its small stainless steel design, it quickly tracks changes in viscosity and temperature to within ±1 percent accuracy, the same precision that many lab instruments provide using the prescribed ASTM D445 test procedure. Moreover, it is unaffected by vibration or flow conditions making it ideal for engine or dynamometer applications.

Fuel system design for both diesel and gasoline engines can also benefit greatly from engine oil viscosity measurement. Some of the most important fuel economy parameters are difficult and expensive to measure. However, fuel dilution and combustion by-products formation can be easily observed by monitoring changes in the oil’s viscosity in real-time. Likewise, the benefit of small changes in design, operating conditions or lubricant additive packages can be quickly detected by monitoring the viscosity of the oil.

Compressor manufacturers face extraordinary challenges because of EPA-mandated refrigerant changes. As the world moves to phase out the use of chlorofluorocarbons (CFCs) to protect the ozone layer, a dramatic change has occurred in new refrigerants. CFC refrigerants have some lubricity. Mineral oil-based lubricants offer an adequate amount of lubrication for compressors. However, new environmentally friendly refrigerants being tested have virtually no lubricity, requiring significant changes in lubricant formulation to provide appropriate wear protection. In fact, many of the future refrigerant candidates are solvents that pose a tremendous challenge to proper lubrication.

According to the manufacturer, by tracking lubricant viscosity online and in real-time, researchers can determine with accuracy whether certain oil/refrigerant combinations or certain operating conditions are likely to lead to wear or early failure in both new and older compressor designs. It is anticipated that the SPL571 will substantially shorten the time required to obtain adequate knowledge about these systems as engineers struggle to make changes to comply with EPA regulations.

Whether you are a design engineer challenged with redesigning an engine or compressor, or simply trying to figure out how to optimize the oil drain interval of your car, viscosity is recognized as probably the single most important property of a lubricating oil. While traditional lab-based methods have a place in routine oil analysis, online, real-time monitoring provides an alternative when transient data is required to track and trend changes in the oil’s viscosity.