08 Apr Synthetic Lubricants Excel in Temperature Extremes
Perhaps better known for their cold-temperature benefits, synthetics are equally beneficial in extreme heat.
Summer is on the way; this winter has really been hard on everything!
We often think of synthetics as low temperature properties maintain flow in sub-zero conditions to lubricate vital components and ensure start-ups on the coldest mornings but with spring on the horizon it’s time to get ready for summer. One of the many benefits of synthetic motor oils is their excellent all-weather performance. What happens to lubricants during the days of summer in the Southwest desert where daytime temperatures routinely climb above 100°F? Driving a vehicle under these conditions stresses lubricants also, but in different ways than driving in subzero temperatures.
Hot operating conditions subject oils to stress that can result in sludge and varnish formation in your engine and transmission, resulting in major damage. There are a bunch of tests that can be run on used oil to help predict sludge and varnish formation, including oxidation, nitro-oxidation, viscosity increase and total base number (TBN) depletion. If you are not interested in becoming a used oil analysis expert, make sure to pick lubricants proven to withstand the heat. One of the main differentiators of lubricants is how long they can effectively fight sludge and varnish formation.
In the southern half of the United States, the chemical reactions that create sludge and varnish are accelerated with high temperatures. As a general rule, chemical reaction rates, including sludge and varnish formation, double with every 10°C (18°F) rise in temperature. So if you live in Phoenix, AZ, your vehicle lubricants better be designed to hold up to these accelerated temperature reaction rates. It takes detailed knowledge of lubricant chemistry and field experience to get it right.
Keeping metal surfaces effectively separated to reduce friction is another concern down in Phoenix, AZ during the summer. Reducing friction will reduce the amount of heat that is generated, which will lower the operating temperature of the component. Anti-wear components help maintain this separation of surfaces, but lubricant thickness is the main mechanism.
When oil gets too thin, friction and heat are generated. Since lubricants generally thin as temperatures go up, they need to be designed to provide effective separation at the highest expected operating temperature. An oil’s base stock and formulation influence this property, called viscosity index (VI), which indicates the change in oil viscosity in relation to temperature. Oils with high viscosity indices have smaller changes in viscosity due to temperature changes than do oils with low viscosity indices; therefore, it is desirable for oils to have higher viscosity indices. As you might expect, synthetic motor oils have higher viscosity indices than conventional mineral-based oils do.
We also rely on engine oil to absorb heat from the contact surface area and transport it to a location where it can be safely dissipated (an oil-cooler or sump). As oils age, they cannot carry away as much heat, so temperatures increase, accelerating the chemical reactions which result in sludge and varnish.
Hot summer temperatures were part of the challenge facing AMSOIL Signature Series Synthetic Motor Oil and Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid during the 2011-12 Las Vegas Taxi Cab Field Study. Over the course of 18 months, test vehicles operated in the fleet’s service area of Las Vegas up to 24 consecutive hours daily, accumulating more than 7,000 hours of service.
Like most taxi cabs, the vehicles operated in stop-and-go conditions where excessive idling is the norm, but they also faced the grueling summer temps of Vegas where daytime highs often exceed 100°F. Hour after hour, day after day, under such punishing conditions, AMSOIL lubricants proved up to the task. Engine and transmission components from the test vehicles were later examined and found to have minimal or no notable wear, even after practicing extended drain intervals.
Few of us operate our vehicles under such severe settings, but it is reassuring to know that AMSOIL synthetic motor oils provide outstanding wear protection and superior high-temperature performance in the harshest conditions. The next time you’re driving during one of those summer scorchers or battling stop-and-go traffic, be assured that AMSOIL synthetic motor oil is working hard under the hood to keep your engine running cool.