What is the Low-Temperature Performance of Motor Oil? The Effect of Viscosity Index Improvers on Low-temperature Performance

Low-Temperature Performance of Engine Oil

The low-temperature viscosity of motor oils is a crucial rheological characteristic. To enable the vehicle to start in cold weather, the viscosity of the motor oils in the bearings must be below a critical value. This value is determined through low-temperature engine start ability experiments and is defined within SAE J300 for all "W" grades.

The viscosity Index Improver has an important influence on the low-temperature performance of multi-grade motor oils, and there are two critical values indicating the low-temperature performance index of multi-grade motor oils: low-temperature start-up and low-temperature pumpability.

Low-Temperature Start Ability

Many factors affect the low-temperature start-ability, one of the most important indicators is the low-temperature viscosity, the smaller the low-temperature viscosity, the easier it is to start.

Generally, Cold Cranking Simulator (CCS) is used to measure the apparent viscosity of multi-grade oil at low temperatures. A cold start simulator is a rheometer operated at a high shear rate at a fixed ambient temperature to simulate the flow of lubricating oil into the engine bearings at start-up. After the engine is started, the oil must also be able to flow freely into the oil pump and be distributed to the various oil lines of the engine.

The low-temperature properties of different VIIs are quite different, and Polymethacrylate PMA Viscosity Index Improver (VII) shows lower viscosity in a wide range of shear rates, so PMA has the best CCS performance.

The molecular chain of Polyisobutylene (PIB) is relatively rigid because it has many methyl side chains, and its viscosity increases rapidly at low temperatures, so the low-temperature performance of PIB is the worst.

Low-temperature performance of the Common Viscosity Index Improver

Chorus Lubricant Additives Company supplies various viscosity improvers and relative motor oil additives, high, medium, and low-end products. Please feel free to inquire about the price and specifications.

Low-Temperature Pump-ability of Motor Oil

When the engine is started at a low temperature, the oil pressure of the lubricating oil system must be normalized in a short time to ensure that all parts of the engine are lubricated in time, otherwise it will cause wear and tear. The ability of engine oil to be pumped to various parts of the engine is called pumping capacity.

The pumpability of engine oil depends on the apparent viscosity under the pumping conditions. Tests have shown that the low-temperature pumping viscosity of multi-grade oil is not higher than 3Pa·s, which can ensure pumping oil supply, and this viscosity is called Critical Pumping Viscosity. The temperature at which the critical pumping viscosity is reached is called the Critical Pumping Temperature, which is measured with a Mini-Rotary Viscometer (MRV). The MRV is a low shear rate rheometer used to simulate the pumpability of a vehicle's multigrade motor oil after idling for two days in cold weather.

SAE J300 also specifies upper MRV viscosity limits for all "W" grade engine oils. MRV can measure both the flow limit of viscosity and the limit of air resistance. The average pumping temperature (BPT) predicted by MRV has a good correlation with the average limit pumping temperature of the engine.

Brookefield viscosity can determine the viscosity flow limit, and The following Table lists the effects of different types of viscosity index improvers on low-temperature pumping performance.
 

For more about the performance of Viscosity Index Improver (VII), please feel free to contact Sales Engineers of Chorus Lubricant Additives Company.