Abstract
Several civilian vehicles in China operate in urban traffic conditions and have their motor oil changed every 5,000 km. This study investigates the variations in oil properties after servicing at 5,000 km, based on systematic road tests (including a repeated test, a parallel test, and a new vehicle test). The physicochemical properties, changes in components, oxidation stability, detergent-dispersant performance, and tribological properties of motor oils were analyzed. The results showed that the total acid number (TAN) of oils increased with the operation mileage, by up to 1.41 mgKOH/g. The total base number (TBN) decreased after the road tests were completed, and the decrease was less than 44.6%. The kinematic viscosity (KV) of most oils decreased initially and then stabilized in the middle stage, before starting to increase later in the experiment. The change in KV at 100 °C was less than 15.96%. The oxidation onset temperature (OOT) of the oils diminished gradually with the operation mileage. All OOT values of the used oils were higher than 210 °C. A spot test indicated that the used oils retained their detergent-dispersant performance to an appropriate extent. The four-ball wear scar diameters and friction coefficient of the used oils did not increase significantly after the road tests were completed. This study can serve as a reference for end-users when changing motor oils.
Highlights
Motor oil provides wear protection, thermal management, and corrosion inhibition functions that are critical to engine performance and longevity [1, 2]
The oxidation onset temperature (OOT) of motor oil was determined by pressure differential scanning calorimetry (PDSC, NETZSCH HP 204, Germany) with American Society for Testing Material (ASTM) E2009-02 as a reference
Half of the single operation time was less than 20 min, and approximately 90% of the single operation mileages were less than 30 km
Summary
Motor oil provides wear protection, thermal management, and corrosion inhibition functions that are critical to engine performance and longevity [1, 2]. Motor oil must be changed to counter degradation and contamination, and to maintain the quality necessary to protect the engine [5, 6]. [11] studied oil-change intervals in Europe from the 1950s to the 1990s. The General Motors Corporation maintenance schedule for gasoline-fueled passenger vehicles and light trucks recommends that the engine oil should be drained every 12,000 km or 12 months, barring severe operating conditions [12]. The reasons may include the operation condition, environmental factors, gasoline quality, and end-user’s opinion on oil maintenance. Five gasoline-engine vehicles were used in several on-road tests under urban city conditions to study the oil degradation. More comprehensive parameters of oils were analyzed in an attempt to determine the accuracy of the oil condition; this can provide end-users with useful information regarding motor oil maintenance
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