Engine oil has been around a long time, and we all know the importance of it, yet it is often one of the most undervalued elements in a vehicle. Some techs don’t like checking it, changing it or spending the time that is now required to ensure that the correct engine oil is being installed in the vehicle they are servicing. But the engine oil that is being used today, especially in a new or brand-new vehicle is a highly specialized and developed product.
When we think about engine oil, the first thing that usually comes up is the correct viscosity that is needed for a particular engine. But viscosity is only a small part of the huge chemical compound that we identify as engine oil. Low viscosity oil is now the norm. 0W-based oils offer improved cold start circulation, reduced engine drag when starting, lower fuel consumption and they allow the engine to produce lower exhaust emissions. But these low viscosity engine oils also allow more flow through the engine when it’s at operating temperature, providing the needed lubrication, friction reduction, cleaning and cooling properties that engine oil must provide.
There are three common engine oil-based concerns that the OEMs and the major manufacturers of engine oils are addressing:
- Crankcase moisture deposits.
- LSPI: Low-speed pre-ignition.
Crankcase moisture has long been a concern in the internal combustion engine (ICE), but what causes it? It is most often visible on the oil cap as a thick, milky slime. Condensation from infrequent driving or short trips, high moisture content fuels (such as high ethanol content fuel), seasonal weather changes, PCV issues, a faulty thermostat, or a failed cooling system that allows coolant into the engine, are all common causes of moisture (water) entering the engine oil.
Not driving enough is a frequent cause of excessive condensation accumulating inside the engine. If the engine doesn’t reach the proper operating temperature, the moisture/condensation that has formed inside the engine will not evaporate and be dealt with by the PCV system and burned in the combustion chamber. The typical short trip is less than 10 minutes, not near enough time to fully warm things up, especially in a cold weather climate.
Moisture in the air (humidity), moisture from ambient temperature changes (warm to cold) and moisture created as a by-product of combustion will condense on the surfaces inside the engine. This moisture will eventually find its way into the oil pan and once in the oil pan, it will be mixed with the engine oil and circulated through the engine. If there is enough moisture, we can see issues that range from illuminated dash warning lights to more severe cases that can result in excessive engine wear or worse.
The OEMs and lubricant manufacturers have long been aware of crankcase moisture formation, but the rise in popularity of hybrid vehicles has brought the issue of internal engine moisture formation and its effects on the engine’s oil to the forefront.
Hybrid vehicles typically function at lower engine operating temperatures while the vehicle is in electric or battery mode. Hybrids perform more frequent stop-start operations and may not reach the best engine operating temperature needed to evaporate the crankcase moisture for extended periods of time. The average hybrid engine can run at least 68 degrees below the operating temperature of the non-hybrid ICE engine. The combination of these events enables crankcase condensation formation. This crankcase condensation will ultimately mix with the engine oil during normal engine operation, becoming combined or emulsified. With hybrid vehicles on pace to outsell traditional ICE-equipped vehicles by the end of this decade, both the OEMs and the oil lubrication companies have developed ways to deal with the unique hybrid operational characteristics and the engine moisture it creates.
Oil and water don’t mix, but the engine oil will have emulsification additives incorporated into its additive package that will allow the water and oil to form an emulsion. This emulsion still needs to supply the needed lubrication and protective benefits that the engine’s oil is intended to provide.
The emulsification performance of today’s engine oils is a balancing act of combining and stabilizing/holding the collected moisture with the engine oil and allowing it to evaporate once the engine oil temperature is high enough. This balancing act is crucial for engine longevity and durability.
The familiar white sludge that we see on the backside of the oil cap is about 40% water by weight and is an example of an emulsification package that could be holding the moisture too well. There are other reasons that can cause the buildup of this white “mud”: bad thermostats, defective cooling systems and internal engine coolant leaks. But this white sludge also shows that circumstances are favorable in the crankcase for increased acid formation that can cause engine bearing corrosion and increased oil pump wear.
On the other hand, if the emulsification package isn’t holding the moisture well enough, it can allow the moisture to separate out of the oil as water. If the separated water in the crankcase reaches excessive levels, water could cover the oil sump and cause oil starvation, with water being pumped rather than engine oil, or cause a freeze, totally blocking the oil pump’s pickup screen, again causing oil starvation.
Several manufacturers have issued TSBs that address the amount of accumulated moisture in the engine oil. Toyota TSB-0104-21 addresses such an issue, on the hybrid and non-hybrid Dynamic Force A25 or M20 engines. The TSB says the following: during freezing temperatures, low oil pressure DTCs P05202A and/or P052477 could be set, low engine oil pressure warning light illuminated, and a milky discolored engine oil could be seen. The TSB goes on to explain that moisture from the engine blow-by gases can build up because of short trips in extreme wintry weather. When the moisture freezes, the engine oil pressure may drop, setting the trouble codes and illuminating the warning light. The fix is to inspect for internal coolant leaks and if none are found, clear the DTCs and change the engine oil and filter.
Soot is a common byproduct of the Gasoline Direct Injection (GDI) system. GDI supplies greater power, better fuel efficiency and allows for higher compression ratios, but it also creates a harsher environment for the engine oil. When the engine is equipped with a turbocharger that only makes the problem worse. The GDI system can change the viscosity of the engine oil due to the system’s operational characteristics, the increased cylinder pressures, and higher sustained combustion temperatures.
The GDI system produces soot during the combustion process, and this GDI soot is a problem. The traditional engine with non-GDI injection created soot in the combustion chamber, and this soot caused the engine oil’s viscosity to increase, and it aided in the formation of damaging engine sludge. The traditional engine oil designed for these non-GDI engines was engineered to deal with this issue and prevent the formation of sludge and stabilize the oil’s viscosity.
GDI soot is a different beast. Because the GDI system atomizes the fuel so efficiently in the cylinders when it is sprayed, it increases the available surface area of the fuel to burn, and this leads to the formation of GDI-based carbon soot.
GDI-created soot can be deposited on the cylinder walls and then is scraped off into the engine by the piston rings, where it finally ends up in the engine oil. Once in the engine oil, the oil’s additive package will break down, diffuse and encapsulate these soot particles, preventing or limiting them from causing any abrasive engine wear. Some of these oil-captured abrasive particles will be filtered out by the oil filter, but the traditional GDI soot particle is often too small for the oil filter to filter out.
GDI soot will, to some extent, thicken or increase the oil’s viscosity. But because of the different chemical structure and chemistry of GDI soot, it is now linked to the increased wear of various other engine components that typically did not show wear from combustion chamber soot. When GDI soot is combined with the acids and the diluted fuel in the engine oil, GDI soot has been directly linked to the accelerated wear of the engine’s timing chains and other vital engine components.
Fuel dilution, on the other hand, can dramatically lower the engine oil’s viscosity. The fuel dilution can be a result of the GDI system injecting the fuel directly into the cylinders. When the engine is cold, the injected gasoline can condense on the cylinder walls, and like the GDI soot, it is scraped off by the action of the piston rings and into the engine oil.
Fuel-diluted engine oil can accelerate wear on pistons, piston rings and cylinder walls. It also reduces the engine oil’s ability to stop deposit formation (engine sludge), acid formation, oil oxidation and can lead to higher oil consumption.
LSPI: Low-Speed Pre-Ignition is a random, uncontrolled combustion event that occurs inside an engine cylinder before the spark plug can ignite the air-fuel mixture. LSPI most commonly affects small displacement turbocharged GDI (TGDI) engines under a low-speed, high-load situation, such as starting off from a stoplight. LSPI can cause loud knocking noises and result in catastrophic engine damage. LSPI is caused by the collision of two pressure waves in the cylinder. When the ignition system fires the spark plug, the air-fuel mixture is ignited and causes a planned pressure wave. But when LSPI occurs it will create an unplanned pressure wave, and that’s a problem. When these two pressure waves collide in the cylinder, an enormous amount of energy is released at the point where they meet. This energy causes the loud knock or super knock that is often associated with LSPI, but cracked or destroyed pistons and other devastating engine damage is also common.
What causes LSPI and how is it related to engine oil? When the piston is heading downward during the intake stroke, the GDI injector fires. The injected gasoline will wash the thin layer of engine oil kept in the honing valley marks (for lubrication of the piston rings and the piston) on the cylinder wall. This mixture of engine oil and fuel will become liquified, and will leave a section of the cylinder wall unprotected without any lubricating oil, increasing cylinder wear.
As the piston heads upwards during the compression stroke the liquid mixture of fuel and washed oil will be scraped from the cylinder wall by the piston rings and form small puddles on the top of the piston or between the piston rings and lands. As the piston continues to travel upwards on the compression stroke, the conditions in the combustion chamber can cause this fuel/oil mixture to ignite creating an unintended pressure wave. This is the LSPI event. With the piston still traveling upwards the spark plug will ignite the remaining air/fuel mixture creating the planned pressure wave that will collide with the unintended LSPI pressure wave. When these two pressure waves collide, their energy is combined, and this energy is enough to damage connecting rods, crack pistons, and over time cause sections of the piston to break away completely.
The LSPI problem can be addressed in diverse ways. Ensuring the customer is using the correct octane fuel and keeping the combustion chamber clean and free of any deposits can lower the risks of LSPI. Manufacturers can use the engine management system to over-fuel the engine under certain operating conditions, but that reduces the fuel efficiency of the engine. Reinforcing and strengthening the piston is another way of mitigating the effects of LSPI, but again it can reduce engine efficiency.
An effective way that the OE manufacturers and oil companies have developed to minimize LSPI events is through the development of additives that can be incorporated into the engine oil. These anti-LSPI compounds prevent the fuel/oil mixture from igniting and prevent the unplanned LSPI event from occurring. Today’s API SN oils, ILSAC GF-6, GF-6A, GF-6B, and Dexos engine oils are formulated with additives to help reduce the risk of LSPI. It's important to note that LSPI is a complex issue, and while these strategies can help reduce the risk of LSPI, complete prevention may not always be possible.
Engine oil is a continuously evolving product that has become a highly specialized part of today’s vehicles. Gone are the days of the “one oil fits all engines” thinking. Today’s vehicles need highly specific oils that do far more than lubricate, cool, and clean the internal engine components. The engine oil that we use today is highly specific, in some cases even engine specific. It is being asked to perform in a much harsher environment than ever before. And under these extreme operating conditions it is being asked to keep all its initial starting qualities, protections, and capabilities over the extended oil change intervals that we are seeing on today’s vehicles.