As engine-operating conditions grow more severe, so do the demands placed on your motor oil. New engine hardware such as turbochargers, direct injection and variable valve timing (VVT) place increased stress on your engine oil. This, in turn, has led to the introduction of more strict more oil specifications.
Here’s what we’re going to cover:
How strict fuel-economy standards increase engine stress
What is LSPI (low-speed pre-ignition)?
How motor oil helps prevent LSPI
GM dexos and API SN Plus oil specifications
Improved fuel economy
Corporate Average Fuel Economy (CAFE) standards require a fleet-wide average of 54.5 mpg by 2025 in the United States (although the Trump administration is expected to relax those standards). To meet these requirements the automotive industry has focused on smaller, more fuel-efficient engines. In fact, by 2020, industry experts predict that almost every new vehicle will feature gasoline direct-injection technology (GDI). The vast majority will also be turbocharged (T-GDI).
Severe operating conditions
Smaller, more-efficient engines that make the power and torque of higher-displacement engines undergo more severe operating conditions that can lead to…
Severe engine knock, also called low-speed pre-ignition (LSPI)
Increased engine temperatures
Compromised fuel injectors
Increased wear and deposits if the oil isn’t up to snuff
The biggest motor-oil-related challenge on the horizon is LSPI, which can destroy pistons and connecting rods
LSPI, cracked pistons & rods
LSPI is the spontaneous ignition of the fuel/air mixture before spark-triggered ignition. It is another version of pre-ignition. Pre-ignition (engine knock) has been around since the beginning of internal combustion engines. LSPI, however, occurs under low-speed, high-torque conditions, such as taking off from a stoplight in T-GDI engines. This scenario can create conditions where the fuel/air ignites too early in the combustion cycle, throwing off the engine’s timing. The expanding combustion charge collides with the piston as it’s moving up the cylinder, potentially destroying the pistons or connecting rods.
Oil can help prevent LSPI
Experts suggest the cause is due in part to oil/fuel droplets or deposits in the cylinder igniting randomly. The droplets and deposits contain enough heat to ignite the air/fuel mixture before spark-triggered ignition. Oil formulation can play a role in reducing LSPI.
Certain motor oil ingredients can promote LSPI, while others can help reduce it. It’s tempting to think, “Well, dump a bunch of ingredients into your formulations that help reduce LSPI.” But some ingredients that help reduce LSPI have been limited over the years in motor oil formulations for other reasons.
It truly is a scientific balancing act confronting oil formulators. It’s no easy task to formulate motor oils that deliver excellent wear protection, resist the increased heat of turbocharged engines, prevent deposits, act as a hydraulic fluid and, now, combat LSPI. The performance of the entire formulation – not just one or two ingredients – is what counts.
New oil specifications: API SN Plus
Next-generation motor oils need to pass an LSPI test to meet these new demands. General Motors was first out of the gate and required oils to pass its own LSPI test. The updated GM dexos1 specification (known as dexos1 Gen 2) took effect Aug. 31, 2017.
The new American Petroleum Institute (API) specification, API SN Plus, is slated to go into effect as early as May 2018. Lastly, the International Lubricants Standardization and Approval Committee (ILSAC), which for the most part mirrors/honors the API specifications, will have its GF-6 performance specifications set to take effect in mid-2019