The mini-rotary viscometer is a device used to measure the pumpability of an engine oil at low temperatures. Engine oils must meet viscometric standards including those determined by the MRV in order to be classifiable within

SAE J300 SAE J300 is a standard that defines the viscometric properties of mono- and multigrade engine oils, maintained by SAE International. Key parameters for engine oil viscometrics are the oil's kinematic viscosity, its high temperature-high shear visc ...

viscosity grades. The requirement was added after the winters of 1980-81 and 1981-82 caused major pumpability field problems in the US and Europe. Different MRV test procedure exist; for example

ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...

D4684, required for SAE J300, involves heating the oil to remove its "memory" then cooling it at a controlled rate over a period of more than 40 hours to the test temperature.https://www.tannasking.com/documents/17/MRV_TP-1_Brochure_2019-01-08.pdf

D4684 is done with fresh oil, so the MRV result may not be representative of used oil pumpability. Some motor vehicles manufacturers specify used oil MRV requirements.

References

{{reflist Lubrication Viscosity meters