An internal combustion engine is really hard on oil. Want proof? Of all the different types of lubricants, from hydraulic fluid to gear oils, motor oils contain the most additives and feature the most advanced chemistry. Why? Simply put – combustion. The temperatures, pressures and contaminants of combustion place great demands on the lubricant. The oil must not only lubricate, it also has to clean and cool the engine.
In engines featuring variable valve timing, the oil must be a hydraulic fluid as well.
The majority of variable valve timing (VVT) engines use motor oil as a hydraulic fluid to run the timing mechanisms. This change adds a whole new wrinkle to what you need your motor oil to do. In addition to providing anti-wear and fluid film protection for your engine, the motor oil in a variable valve timing engine must also resist foaming and shearing. Both of these events will affect the performance of the VVT system.
Obviously foam is a poor lubricant, and it is an even worse hydraulic fluid. The air can be compressed, and a good hydraulic fluid should be basically incompressible. If your motor oil foams, you could be in trouble.
The other area that could affect the performance of the VVT is shear stability. Viscosity is the most important property of a lubricant, and motor oils are required to work over a very wide range of temperatures – think starting a car in Minnesota in January and driving a car in Arizona in July. To improve the viscosity attributes of the oil, polymer additives called Viscosity Index Improvers are added to the motor oil. These Viscosity Index Improver polymers can be degraded under high shear conditions. Think about stretching a rubber band. Pull too hard and it breaks. This can happen in VVT engines as the oil is being forced through the narrow passages of the VVT under high hydraulic and mechanical load.
The shearing or breaking down of the Viscosity Index Improver polymer leads to lower oil pressure and degraded viscosity characteristics. Both of these conditions will affect the performance of the VVT system.
A secondary effect of both foaming and shearing is increased oxidation, and that will shorten the life of the motor oil. As the aerated and sheared oil interacts with the oxygen in the air (and unburned Ethanol blended fuel), oxidation of the motor increases. If the oil becomes highly oxidized, the engine can be harmed by the deposits and acids left behind by the oxidized motor oil.
A high performance engine that utilizes VVT technology needs to be filled with high performance oil that resists foaming and provides shear stability.
The hydraulic industry recognizes the KRL shear stability test as the standard for determining if an oil is shear stable enough for heavy duty applications.
Owners of VVT engines should look for motor oils that perform well in the KRL shear stability test. Many off-the-shelf brands of motor oil lose more than 25% of their High Temperature High Shear viscosity during the KRL test compared to less than 10% in Driven Racing Oil’s line of high performance street oils.
It is also beneficial to look for an oil with a low foaming tendency. The current API motor oil specification allows up to 50ml of foaming tendency, so obviously a lower tendency would be beneficial. As the engine runs, the crankshaft whips through the oil, causing it to aerate. This aeration gets worse as RPMs get higher, so this is a bigger issue for VVT-equipped cars that see time on the track. The better the air release properties of the oil, the better performance you will see from the VVT. New mPAO base oil (available in all Driven lubricants) offers dramatically better air release properties than conventional synthetic base oils. In the ASTM D-892 foaming test, the mPAO demonstrated more than a ten-fold reduction in foaming tendency compared to equivalent viscosity products. Thus, choosing an mPAO-based product for your VVT engine means inherently lower foaming tendency.
Both shearing and foaming affect oil pressure, which is critical to VVT performance. Brian Reese from COMP Cams explained, “If your oil pressure drops too low, then the cam phasers will not function, so it is vital for the motor oil to maintain solid oil pressure especially during on track conditions.”
Reese added that choosing the correct viscosity for the engine build is the first step in ensuring solid oil pressure.
“Sometimes aftermarket/performance engine builds feature larger clearances for higher RPM operation,” he explained. “This causes lower oil pressure at idle, and can result in the phasers going out of control. Choosing the correct viscosity oil solves that problem.”
Finally, many of these VVT power plants are Overhead Camshaft (OHC) engines, and these cams are driven via timing chains. Proper anti-wear additives are important to protect these chains and gears from wearing during high performance use. For track day car owners that have engines featuring VVT, a motor oil with a little extra ZDDP in it would be helpful.
Keeping the oil changed on a regular basis is also important for keeping the engine clean. Hydraulic systems need to be kept much cleaner than a normal engine, so the requirement to keep the oil and the engine clean with a VVT is much greater. This means changing the oil filter regularly if the car sees a lot of track days, and keeping the oil change interval to a reasonable mileage – no 10,000 mile oil drains here.