Havoline Oils – Part One

The Society of Automotive Engineers was originally responsible for developing a system to classify engine oils, this was known as the SAE Engine Oil Viscosity Classification J300. 

SAE J300 contains two sub-classifications, a “W” grade, relating to the low temperature flow properties of an engine oil and a “non-W” grade designation, relating to viscosity operating temperature properties. W-grade and non-W grade oils are sometimes referred to respectively as the ‘Winter’ grade and the ‘Summer’ grade, hence the “W” we commonly see in oil classifications.  

The numbers before and after the “W” relate to the viscosity of the oil. The number before “W”, represents the oil viscosity at low temperatures and the number after the “W”, how thick the oil is during the engine’s normal operating temperature.

If we deep dive into how the oils are classified, there are a number of technical components to the classification status. Low temperature viscosity requirements are defined by both a cranking viscosity and pumping viscosity measurement. The cranking viscosity is measured by the Cold Cranking Simulator (CCS) test to evaluate the cranking resistance of an engine oil. If the CCS viscosity limit for a specified oil is exceeded, the battery and starter motor may not be able to crank the engine at a sufficient speed to allow the engine to start.

The pumping viscosity is measured by the Mini-Rotary Viscometer (MRV) test. This test also determines the presence of yield stress, assessing the ability of an oil to flow through the oil pick-up tube. If the pumping viscosity, or yield stress of an engine oil are too high, an engine can be starved of oil during the first few minutes of operation. The temperature for the pumping viscosity measurement is 5°C below the cranking viscosity measurement temperature to ensure that oils which help with engine start-up will also pump adequately.

The operating temperature viscosity requirements are defined by kinematic viscosity measurements at 100°C and by high shear rate viscosity measurements at 150°C. There are minimum kinematic viscosity limits for each W-grade, but no maximum, whereas non-W grades have minimum and maximum limits. The high shear viscosity is measured at 150°C and at a shear rate of 106s-1. These are typical conditions in engine bearings during operation.

Oils which meet the requirement of only one sub-classification are referred to as single or mono-grade oils for example SAE 10W or SAE 30. oils, that are labelled as meeting the requirements of both a W and a non-W designated grade, which are called multigrade oils such as 10W-30.

What does the term lower viscosity mean as it relates to oil?

Lower viscosity is a relative term that changes over time. Previously, oils which seem standard today, such as SAE 10W-30 or SAE 5W-30 were described as low viscosity oils when compared to the typical SAE 20W-50, 15W-40 & 10W-40 viscosity oils at that time.

Today, we speak about lower viscosity oil if we have engine oils for which the “W” grade is 5 or 0 and the non-W grade is 20 and lower. Currently, low viscosity relates to multigrade engine oils with a high shear rate viscosity at 150°C of less than 2.9 cP.

It is important to remember that engine oils with a high shear rate viscosity at 150°C of less than 2.9 cP cannot be used in many older engines, as they will lead to excessive engine wear and eventually engine seizure. Today, several engine manufacturers are developing engines than can cope with engine oils with high shear at 150°C of 2.3 cP and lower.

What are additives and why are they so important?

To function effectively engine oil requires chemical components called additives. Additives help protect the engine and improve and maintain the performance of the engine oils. Without the addition of high performing additives to the base fluids, oils would not survive the conditions created in a modern engine. 

An engine oil consists of a base fluid with a combination of different additives in complex and carefully balanced formulas. Depending on the specific application, various combinations of additives are used to meet the required performance level.  Each additive has an important role to play in protecting and optimising the engine, some of the most important of which we can see in the list below.

• Detergent is used to neutralise inorganic acids formed during the combustion process and to neutralise organic acids formed by oil degradation to prevent corrosion of engine parts. They also clean the engine surfaces by removing, suspending, and dispersing the lacquer and varnish that may form as the engine oil ages. 
• Dispersants suspend and prevent clustering of deposit particles, soot, oxidation products, sludge etc. formed in the engine oil.
• Anti-wear additives reduce bearing corrosion and control wear.
• Antioxidants are key to slowing down the process of oxidation, which occurs as base oils are exposed to oxygen and heat in the engine. 
• Viscosity modifiers are added to reduce the viscosity-temperature dependence of the base oils. This additive enabled the development of multigrade engine oils. The primary feature of multigrades is that they allow the engine to start at low temperatures, while providing sufficient viscosity at elevated temperatures to protect the engine against wear.
• Pour point depressants cannot prevent wax crystals from forming, but they minimize their effect and may also benefit the low temperature pumping viscosity of an engine oil. Base oils founded on hydrocarbons contain paraffinic components form waxes at lower temperatures resulting in a network of wax crystals that prevent the oil from flowing correctly (the temperature at which this happens is called the pour point).
• Foam inhibitors help to contain the presence of foam, which can result in reduced oil pressure, leading to engine damage. Air entrainment or agitation is also an issue as it can lead to the cavitation of the oil film in bearings and possible failure. 
• Friction modifiers play a part in engine fuel consumption and were introduced to reduce friction losses due to piston liner/piston ring contact and bearing and valve train friction.
  

Further information on the full range of Texaco Havoline products can be found here.