Lubricants are essential for the proper functioning of an internal combustion engine and deserve daily attention from agricultural machinery operators. Lubricants in oil form are classified according to their viscosity (SAE) and quality (API). When starting the working day, the engine oil level must be checked and, if it is below the level indicated by the manufacturer and observed on the oil dipstick, top up, Figure 1. This maintenance must be carried out with the tractor turned off, the engine cold and in a level place. Any strange noise, excessive smoke in the exhaust pipe or unusual smell requires greater attention.
But when is the ideal time to completely change the lubricating oil? Some experts recommend replacing the lubricating oil every three months. For tractors that operate daily, it is recommended that the change be made every 200 hours of service. During the process, it is essential to observe the information in the machine manual and the specifications of the lubricating oil used.
It is recommended that, when changing the lubricant, the producer also replaces the oil filter and carries out maintenance on the engine air filter. Observe your machine's manual to meet the stipulated deadlines and do not delay this maintenance. A good functioning tractor will be the result of good maintenance.
Lubricants can be produced based on substances of mineral or synthetic origin, generally those of mineral origin have a reduced production cost and are therefore more common. Oils of synthetic origin are produced in laboratories.
The main function of lubricating oils is to reduce contact between the metal parts of the engine, reducing friction, which will significantly reduce wear on the parts. Lubricants also serve to reduce engine noise, as the parts move more easily, and control the engine temperature, as metal parts operating with friction generate heat. Furthermore, the oil has the function of cleaning the components, protecting against corrosion and the formation of acidic agents inside the engine. In other words, lubricating oil in good condition will promote greater engine efficiency, lower fuel consumption, lower maintenance costs, which aims to lower operational costs for rural producers.
The main characteristic of a lubricating oil is viscosity, which is a physical property that guarantees the fluid's resistance to flow. This viscosity may change by around 10% when compared to a new product. With the use of lubricating oil, what is observed is a decrease in viscosity, the popular saying “the oil is thinning”. This phenomenon occurs when the oil meets the fuel, which ends up leaking from inside the piston as the piston rings wear. A more used engine will suffer greater contamination. By reducing viscosity, a lubricating oil loses its main function and exposes the contact between the metal parts of the engine.
In some engines it is possible to observe a greater viscosity of the oil, becoming thicker, this phenomenon occurs due to the accumulation of dirt in the lubricant, resulting from the burning of fuel, dirt in the air that enters the engine, small particles of metal and humidity. An oil with a high viscosity will make it difficult for the engine to operate, as it will spread less between the parts, increasing fuel consumption and temperature.
When choosing a lubricating oil you have probably already looked at the following classifications: for example SAE 5W-30. But after all, what does this information mean? The acronym SAE comes from the American organization Society of Automotive Engineers, the body that created the parameter that standardizes and classifies the viscosity of lubricants.
The numbers 5W-30 are a reference to the viscosity of this product. We can identify that it is a multiviscosity oil, as in winter it has a viscosity level of 5 and in summer, 30. The letter W comes from the word winter, winter in English. When the engine is at milder temperatures, the oil has a “thicker” viscosity and, as the ambient or engine temperature increases, the oil adjusts to the need, starting to operate with viscosity 30. If the numbers shown on the product packaging are larger, it means that the oil is more viscous, popularly, thicker.
This technological advance was excellent for increasing the useful life of the internal combustion engine, in this way the lubricant adjusts to the engine's needs, adapting the viscosity to the engine temperature.
The information on which oil to choose for your machine must also follow the manufacturers' recommendations that are described in the tractor manual. Do not use lubricants of different viscosities in your equipment, this will certainly reduce its useful life and cause damage.
Another classification that we observe on the packaging of lubricating oils refers to the place of use and the quality of the product, this was prepared by the American Petroleum Institute (API), being divided into three categories and represented by letters. Internal combustion engines that use spark plugs to explode the fuel (OTTO cycle engines) must be lubricated with API “S” oils. For diesel engines (Diesel cycle engines), the acronym API “C” is used. Finally, the lubricating oils for gears are API GL, where “GL” indicates gear lubricants in English.
The letter that accompanies the classification of place of use refers to the quality of the product, generally linked to the quantity of additives present in the lubricating oil. In other words, CB oil is of better quality than CA oil and both are used in a Diesel cycle combustion engine. This improvement refers to the quantity and quality of the substances used in the manufacture of the product. These chemical substances, called additives, can be added to oils for specific purposes, seeking to increase desirable characteristics and minimize undesirable characteristics. There are different types of additives on the market, as you can see in the table below.
Always follow the recommendation in the tractor manual to choose which lubricant meets the needs of your machine and be sure to carry out the maintenance referred to in this article, they are quick, easy and somewhat cheap in view of the damage that may occur if you do not change them. the lubricant.
Dispersant detergents: substances that minimize the formation of carbon residues, produced during combustion.
Antioxidants: additives that prevent oxidation.
Anticorrosives: They protect metal parts from corrosion, being able to protect the metal from humidity and/or protect the metal from other corrosive substances.
Defoamers: prevent the formation of foam, which limit the lubrication capacity.
Extreme pressure: substances that prevent the film formed between contacting parts from coming apart.
Viscosity index improvers: substances that act depending on temperature variation, with the aim of reducing the effects of temperature on the viscosity of oils.
Pour point depressors: They are designed to prevent the accumulation of paraffin crystals, which obstruct the circulation of oil.
Antifreeze: compounds that prevent lubricants from freezing at low temperatures.
Flávio Coutinho Longui, UFBA; Daniel Mariano Leite, UNIVASF; Marconi Ribeiro Furtado Júnior, UFV
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