Low-Temperature Compatibility of Engine Lubricants and the Risk of Engine Pumpability Failure

An investigation of an engine field-failure found low-temperature incompatibility to be the root-cause of an engine pumping failure. This was established from an examination of the rheology of the new and used oils. It was later discovered that some SAE multigrade oils that contain higher-cloud-point basestocks are incompatible with other same-W-grade oils that contain VI improvers that have a propensity to interact with wax precursors. The latter oils, which failed the Scanning Brookfield test, but not the TP1 mini-rotary viscometer test, were found to be incompatible with a number of commercial multigrade oils at low-temperature.