LO 10-3 Identify and describe the purpose and function of oil additives

1. Oil Additives

Oil Additives

Motor oils are typically comprised of 75–85% base stock, which is the raw mineral oil processed from crude oil. The remainder of the oil volume is made of chemical additives Figure 22. Additives improve the original properties of base stock oil. Enhancing the performance of motor oil base stocks is necessary to adjust the performance of the oil to suit its intended application. For example, diesel engines produce higher levels of soot than gasoline engines, which is why engine oil turns black more quickly in diesels than in gasoline engines. This soot tends to clump together, leaves deposits inside the engine, and even thickens the oil. To prevent this, more detergent is added to diesel engine oil, causing the soot to stay suspended in the oil Figure 23. To understand the function of detergents, consider washing dishes with and without soap detergent. Dishwater will stay dirty if it contains detergent to keep the dirt suspended in the water. Without detergent, the dirt eventually settles out of the water to the bottom of the sink. By keeping soot (dirt) suspended, the filters can remove more soot from the oil and leave the engine less likely to build sludge deposits.

FIGURE 10-22: Relative values of viscosity improvers and detergents in diesel engine oil.

FIGURE 10-23: Diesel engine oils are formulated to tolerate the increased quantity of soot from diesel combustion. Retarded injection timing and the use of EGR contribute to higher soot levels in diesel-engine lube oil.

Additives also add performance characteristics to base-stock oils to suit a particular application. The use of VI improvers is an example previously mentioned. Antifoaming additives are critical to oil used in engines with hydraulically actuated electronically controlled unit injectors (HEUI) to prevent the aeration of engine oil. Aerated oil causes changes to injection timing and the pressurization of fuel, resulting in low power and poor fuel economy. Aerated oil does not lubricate parts very well and interferes with the delivery of the correct oil volume to engine components.

1.1. Video: Oil Additives

1.2. Common Oil Additives

Common Oil Additives

There are many additives commonly used in diesel engine oil:

• Pour point depressants lower oil’s pour point in cold conditions.
• Anti-wear additives protect against metal-to-metal contact under high pressure conditions when oil viscosity is low.
• Detergents and dispersants keep internal engine components clean and prevent the thickening and sludging of oil.
• Oxidation inhibitors maintain oil viscosity stability between service intervals. Oil reacts with oxygen in the air by thickening, particularly at higher temperatures, and forming deposits. Oxidized oil will also begin to corrode metals, such as lead, in bearings.
• Corrosion and rust inhibitors protect engine parts against the effects of condensation.
• Antifoaming additives minimize oil foaming and the cavitation erosion of metal parts.
• VI improvers prevent oil from thickening when cold and thinning when hot.
• Emulsifiers prevent water from combining with engine oil.
• Reserve alkalinity additives ensure that the oil does not become acidic from combustion byproducts. Sulfur in diesel fuel produces acid-like corrosive effects over an extended period of time.

1.3. Aftermarket Oil Additives

Aftermarket Oil Additives
The cost for an oil manufacturer to test and certify engine oil to API standards easily runs in the range of hundreds of thousands of dollars. Profits made from API-certified oil, which retails for a few dollars a liter, is small in comparison to the huge profits made by aftermarket additive marketers on a single bottle of additive. Despite the carefully exacting standards to which engine oil is refined, the advertising of engine oil aftermarket additives leaves the impression that regular engines’ oils are inadequate. Claims made by aftermarket additive makers range from substantial increases in fuel economy to reduced engine wear, increased horsepower, increased cleanliness of engines, and elimination of engine oil leaks. Evidence supporting these claims rests heavily on customer testimonials and little on verifiable testing of products by independent labs. In fact, in recent years, a number of high-profile additive marketers have been prosecuted for making unsubstantiated claims about their products.

1.4. Oil Additive Categories

Oil Additive Categories

Technicians, as well as fleet and service managers, are frequently approached by product representatives promoting the use of aftermarket oil additives. It is important that these products be critically evaluated before they are used to avoid potentially severe economic consequences. Note too that aftermarket oil additives go through no standardized testing except by the U.S. Environmental Protection Agency (EPA) to certify that they are not toxic. An EPA test does not support any additive performance claim made by an additive maker. Common aftermarket oil additives and problems associated with each include the following:

• Products that are simply heavier-viscosity oil or additional VI additives that can reduce oil consumption. In the latest engines, more VI additives not only increase fuel consumption but also potentially starve bearings of circulating oil in much narrower oil clearances.
• Products containing polytetrafluoroethylene (PTFE), otherwise known as Teflon ® , mixed with high-viscosity motor oil. This powdery substance was claimed to be capable of coating engine parts with a protective film to reduce friction. However, a substantial body of evidence indicates that PTFE additive dumped into engine oil can in fact plug filters and small internal oil passageways. Many other tests and studies have demonstrated that PTFE additives actually increase engine wear.
• Products containing regular engine oil, including standard additives with the addition of zinc dialkyldithiophosphate (ZDDP). This zinc compound is added to many oil products already as an extreme pressure additive to minimize damage when metal-to-metal contact occurs. ZDDP must be kept to minimal values; field testing of engines with excess additive has found that the intermediate copper layer of bearings is often corroded through galvanic reactions when extra zinc is added to the engine oil.
• Products containing the same additives already used in major brands of oil but in different quantities and combinations. Engine-industry experts object to the use of these additives because they can disturb the delicate balance between base stock oil and additives already contained in the certified oil. Unintended chemical reactions can take place between these additional additives and the engine parts or additives already in the oil.