1-What engine oil does?

The main tasks of motor oil are lubricating the moving parts of the engine, to minimize friction and wear, help to reduce the heat and to capture dirt, dust and sludge deposits resulting from combustion.

Because motor oil must do more complex work simultaneously, requires a complex chemical formulation but because you know how to operate motor oil, how is ranking and how to choose the right kind of it for your car, you don't need to be a chemist or chemical engineer. Just it is enough that you are familiar with different types of engine oil, its classification and symbols and abbreviations.


2-    Types of oils, at the moment the car engine oils are divided in to 3 types:

A: Mineral (organic)

B: Synthetic

C: Semi-synthetic (Premium)

A: Mineral, is made on the basis of crude oil and the oil that has been used in cars and all of us are familiar with it.

B: Synthetic oil, it is oil that produced from chemical composition or olefins and not with crude oil refining. This type of oil was used first for jet engines. Because of benefits that has this type of oil and compared to mineral oil, in recent years increased its used in vehicles. Synthetic oils have different types with different ingredients which they are also distinct in terms of quality and type of consumption. Among of the types hundreds of synthetic oils with different formulations that each one also has advantaged and disadvantages, the kind that is built on Polyalphaolefins base (PAO) and has small amounts of Ester, is more efficient. We can be cited following benefits for synthetic oils:

1.     Reduced oil consumption due to more life of oil.

2.     Non- corrosive and non- toxic

3.     Low  evaporation

4.     High burning temperature

5.     High resistance to oxidation

6.     Having a high viscosity index in the normal way( quick reaction to changes in temperature)

7.     Reduce fuel consumption to 2/4 %

8.     Low flow point

9.     The ability to use of oils with high viscosity without fear of polymers failure (in the following will be given explanation) the disadvantage of this type of oil is high prices and lack of full compliance with the engines of date technology.

C- Semi- synthetic that is a mixture of synthetic and mineral oil, this type of oil hasn't quality of synthetic oil but in difficult conditions, like high temperatures or high pressure has better performance than the type of mineral and more used in vans and SUV, its price is also a little more of minerals.

To see which of these oils is right for your vehicle; best source is car guide notebook or labels inside the engine box. (If didn't specified the type of oil, meaning that used the same old kind of mineral.)

The use of mineral oil or semi-synthetic can be dangerous for motor that recommended for it the use of more synthetic oil, but in contrast the use of synthetic or semi- synthetic oils of motors that are designed for use in mineral type (old engines) is permitted with specific measures of synthetic oils producers. But many experts know this is wrong to the following reasons:

1-    Each of the different types of synthetic oils according to chemical  formula, don't have ability to comply with certain types of rubbers and elastomeric and as a result, if use of synthetic oil with special formula for engine with gaskets and sealants that oil isn't compatible with the formula, will be causing oil leakage and such issues.( mineral oils causes swelling gaskets and prevent it's leakage, but synthetic oils don't have this property about some gaskets and even some of them lead to corrodes some of gaskets.) In this regard even the use of synthetic oil with ingredients that is different from what is listed in the instruction manual car, for cars that work with this type of oil also can be dangerous, very likely use of these oils in the engines that designed according to use of mineral oil. For example, synthetic oil on the base of Polyglycol or Polyesters, polycarbons, ABS, polyvinylcolorines, (polyphenylene oxide all of these are plastic) and BunaS, Butyl, Neoprene and natural rubber (all of these are elastomers) hasn't good compatibility or synthetic oil base on PAO that the majority of synthetic oils on the market are based on it, (because of properties similar to mineral oils) has poor compatibility with natural rubber, EPDM, butyl, Buna S, that all of them are elastomers. List of synthetic oils and their ability to adapt with variety of rubber and elastomers are to be considered later also solubility of each in additives and engines sludge with properties and number VI.

2-    Synthetic oils compared to mineral oils sits on engine parts with a thinner layer (because the distance of fixed and movable parts of motors that work with synthetic oil is less.) So the use of this oil for engines that are designed with the old technology of mineral will cause leakage of piston. Of course, this case with acceptable reason will be rejected by manufacturer of synthetic oils. But in practice, this problem is seen in older cars. However if you used years from mineral oil and your vehicle has old technology, avoid the use of synthetic oils, but if you have a car with a new technology and you ensured from safety of change the mineral oil to synthetic or semi-synthetic, used of type that made on the basis of PAO, and also don't forget that by switching of oil from mineral to synthetic, cooked sediments of mineral oils are cut from engine parts and immersed to the motor and after a while engine disable, so before switching, should the engine or completely descaling Or used of flushing oil. ( this type of oil only is for cleaning the motor) in this way discharged the mineral oil without filter switching and replaced flushing oil and let the engine idle 20 minutes. After that you can vacated flushing oil, switching filter and replaced synthetic or semi-synthetic oil. Some notes: semi-synthetic oils are mixture of mineral oil and synthetic and can causes the same problems of synthetic oils for made engines of mineral oils. In cars that recommended use of synthetic oil, be sure to use the specified type and whereas for contract of production company with a particular oil company, only the name of related oil listed in guide book and avoided a more detailed explanation about it and on the oil container hasn't explained about type of the ingredients, use only the same type of oil. If you are insisted that switching oil of cars from mineral to synthetic, choose PAO, the kind that include the most synthetic oils available in the market. Because more than the other types of synthetic oils similar to mineral type.

3-    Viscosity of oils

Viscosity of motor oil is a physical property of fluids that depend on their resistance to flow. If the viscosity of fluid is higher, to create the same shape, the more cutting stress is required. For example the viscosity of honey is much more of milk viscosity. Fluid viscosity depends on temperature, this means that with increasing the temperature, viscosity is decrease and with low temperature, viscosity is increased. Also is known oil viscosity by the name of weight. Oils with different viscosity are produced for different weather conditions. Use of high-viscosity oil in winter delay lubrication of engine to warm-up time and during this time oil will not reach to all parts of the engine. In contrast, the use of low viscosity oil in the summer is also causes the friction of engine parts. So selecting the proper viscosity for engine oil a car is dependent to weather conditions. However, recently with multi-grade oils or few-viscosity, need to change the oil somewhat relieved, relatively by the change of season or weather conditions. But use of only one type of mineral multi-grade oil for all of seasons isn't recommended for reasons that will be explained below.

Society of Automotive Engineers (SAE) for convenience classified oils viscosity by a series of numbers. This classification for engine oils is between 0 and 60.

Summer oils that have sufficient concentration at high temperature have viscosity numbers in the range of 30 to 60 (as the air is warmer it should use oil with a higher viscosity number) and the winter oils that easily flow at low temperatures have viscosity numbers in the range of 0 to 25(as the air is colder must be used of oils with low viscosity number.)

For easier cognition, after the viscosity number of winter oil inserted letter W which is contract of winter, also because this classification has been developed by the Society of Automotive Engineers, always before the viscosity number is written SAE. Oils that have one viscosity called single- viscosity, but oils that in recent years produced with the help of chemistry and with polymer to base oil have the ability of different viscosity in different temperatures. This makes that oil in all weather condition to have necessary concentration, this affair addition to increasing the engine life also will be reduces fuel consumption. Therefore, single-viscosity oils are being phased out and only use of these oils in passenger cars is for Race cars motor which has heater or oil heater.

SAE code in multi-grade oils is two parts, first number that comes with the letter W is related to lowest viscosity oil and the second number represents the highest viscosity oil. But as mentioned, multi-viscosity oils are made by adding polymer to oil, these polymers allow to oil that in different temperatures have different viscosities, in cold weather polymers are accumulated and causing the oil to flow more easily. And in the heat polymers start to open up like long chains and oil become thick. But this increase and decrease the viscosity is only for the same oil to a certain extent, for example 10, W-30 oil, is oil with 10 viscosities that at the time of warming will not be more 30. This means that if for example the oil in 100 degree reach to 30 viscosities, at higher temperatures also will not find more than 30 viscosities. This is due to the increased amount of polymer to achieve the maximum number 30 for oil 10.

What need to be considered about use of this oil especially in colder climate, is choose the oil with minimum viscosity distance. This means that in winter due to the low temperature and in summer with hottest temperature of region where you live, choose the ideal oil and avoided from use of oils that don't support very high temperatures to very low temperatures. Because polymers of these oils are very much and these polymers have been broken after a while and combined with sediments of oil and this can causes to adhesion ring or such problems. (The use of these oils are more harmful in diesel engine), oils 5, 5W-30, 5W-40, 5W-50 and 10, W-40 with a range of 25 to 45 are of such oils. (Synthetic and semi-synthetic oils are exception)

You might say oil 20 W-50 also is oil with the extent of 30 per and like 10 W-40, but it isn't because it started from heavier base 20 and for viscosity and to reach the 50 needed to have lower polymer to oil 10W-40 that is from base 10 and must have the ability to reach number 40. Hence, 10W-40 oils by less car manufacturing  is recommended and even some of  factories to know that use of this oil equal to outside vehicle from warranty. So, as far as possible in the case of mineral oils tries to relative of weather the residence selected less distance between the two SAE number and whatever the winter viscosity of number is lower for viscose and reach to higher viscosity number needed more polymers and it is harmful for your engine. Due to weather conditions in most parts of Iran, between the oils in the country (as regards the viscosity) have good performance oils 20W-50 for temperatures between -10 to +40 and 25W-50 for temperatures between -5 to +40. (25W-50 and 20W-50 oils in summer heat have similar situation and only in cold condition, between -10 to -5, will flow better 20W-50 oil. But 25W50 has lower polymer.) Of course, by the above reason 20W-40 oil is a better choice for the winter. But unfortunately this kind of oil found lower in our country. Also if you are in cold place like Azerbaijan or Chahar Mahal (temperatures below -10 °C) and have to use oils with winter base 10 or 5, be sure to try use of multi-viscosity oils that isn't second number more than 30.

4-    API codes

With ever improving technology engines, motor oils also with this improving have changed the quality level and type of additives.

America petroleum institute (API) for classification and separation of oils, acting special coding in terms of quality and manufacturing technology. These codes are two letters; the first letter indicates that the oil is for use in diesel or petroleum cars; if the code starts with the letter C (it is abbreviation of commercial,) the oil related to use in diesel cars and if the code starts with the letter S (it is abbreviation of service) that use in petroleum cars. But the second letter that is indicative of the quality and technology, according to the English alphabet started from A and so far about petroleum cars upgraded to M letter (2005) and about diesel cars to I.

About diesel automobiles after these letters in some cases are seen the numbers 2 or 4 that indicated the oil built for 2-stroke engines or 4-stroke. Note that always kind of upgraded oil (with code above) also has the properties of previous type that can be used from these in cars which older types of oil suggested in its guide notebook. But use of older oil (with lower code) is very harmful of motor that recommended for it oils with newer code.

Some oils have capability of needs related to diesel and petroleum motors and this type of oil is written in binary code 2 that always the first code related to diesel cars and second code is related to petroleum cars, for example API CD/SH.  In below table API codes for gasoline cars are classified on the basis of cars years that of course this table doesn't match with many of our production cars, because in Iran produced cars with technology more than 20 years ago like Pride 94 (2005). It should be noted, in addition to API other types of oil are also present including ILSAC, CCMC, due to its low prevalence, and we will refrain from addressing them.

5-    Symbol

API logo (in general, due to the standard of API numbers in the world, all of oil producers used of these codes to introduce oils produce technologies. But if oil motors of company have been approved by API, the API logo inserted on it. This logo represents the following items. The upper half shows the API code, the middle part shows oil viscosity, the bottom part indicates whether or not consumption oil will reduce fuel consume. If you see something written here like Energy Conserving, means that this oil with reduce of friction in the engine reduce fuel consumption to 5/1 %. Also if the oil able to reduce fuel consumption to 7/2 %, it is called Energy Conserving 2.

6-    Oil change time

New oils with the help of advanced technologies and different additives have long-term goals. But always only written function (in Km or time, whichever occurs sooner) on the oil container isn't criterion of change time, so with increased of below items, must be accelerated change time:

1-    Function in difficult conditions like high engine speeds or overload.

2-    The idle of car (such as driving in heavy traffic)

3-    The number of starter in cold weather

4-    Unadjusted engine

7-    Zinc additives

Zinc as an additives, to avoid of metal to metal friction added to oil, normally when oil doing its job well, it rarely ever happens, but in this situation, zinc reacts with metal and prevented from oil scratching. 11% of zinc (from 100% of additives) is enough for normal use, in motors that operated at high speeds or have turbocharged needed more information. But also know that more zinc, doesn't protect more, so has longer protection and if the metal-metal contact is extremely high, high level of zinc can cause the deposition. Detergent or lotion can cause acid deposition that are produced from water and fuel, absorbed of oil and prevents of precipitation and affix of them on parts. Of course about cars that worked long time with old oils without detergent (or by old poor detergent), use of oils with advanced detergents causes the adhering sediment to engine parts cutting and causes motor failure. Hence, despite the API recommendation and oil producers about use of oils with API code in old engines, try you don't use of oil that has much more API code that proposed to your car. In addition of detergent and zinc those are main base of oil additives, other substances additives to prevent of foaming, oxidation, corrosion, rust and….. .

8-    Technical information about oils

VI, viscosity index is viscosity sensitivity of oil to temperature changes and whatever it has higher number, oil will be performance better. Flash point is temperature that oil vapor in it and according to centigrade degree and with F suffix can be seen on some oil cans. F 400 is acceptable minimum of flash point and always more F is indicator of better oil. Sulfated Ash is solid substance that remains of burning the oil. High levels of this substance may survive deposits on engine parts and low levels also increased the life of the valves.

9-    Some notes, observe the following tips will increase engine life and better performance:

1-    With anytime of oil change, replaced the oil filter. (regardless of how it works)

2-    Avoid of mixing the oils with each other.

3-    After starting let the engine 15 second idle and then drive some time with low speed.

4-    Do not use additives, because may don't much with oil additives, whatever is needed existing in its oil.

5-    Do not uses of oils that past over 3 years from manufacture date.

6-    Black oil isn't a sign of quality, but also means that oil isn't capable of absorbing acidic particles and impurities.

7-    If you use years of mineral oil, don't attempt to replace these oils with synthetic or semi-synthetic oils. (even with flush oil)