Oil for a diesel

Diesel engine oil differs from gasoline engine oil in other characteristics and properties. This is due to the difference in their operation, as well as the conditions in which the lubricant has to work. In particular, a diesel engine operates at lower temperatures, uses leaner fuel-air mixture, and the processes of mixture formation and combustion are quicker.

Therefore, in order for the oil in the engine to work effectively, it must differ in certain chemical indicators. What it should be better, you can find out in this article.

How to choose the right diesel engine oil

There are several parameters that a car owner should always take into consideration when choosing a lubricant. There are three main characteristics of engine oil:

  • Quality — the requirements are defined in the API/ACEA/ILSAC classifications.
  • Viscosity — shown in the SAE standard.
  • Oil base — mineral, synthetic or semi-synthetic.

The relevant information is indicated on the oil package. However, the owner of the car must be aware of the requirements of the car manufacturer. Therefore, first of all, be guided by the standard and tolerances, which are specified in the manual of the car.

Why does a diesel engine need special oil?

There are separate requirements for oil for a diesel engine because the oil is saturated with soot much more than in a gasoline engine, not as a result of fuel combustion. Correspondingly it ages much quicker, loses its protective and detergency properties, and also gets oxidised. Consequently, oil selection should be based on Total Base Number (TBN) and Acid Number (TAN) values. These show how long an oil can hold soot without harming the engine.

What kind of oil should be used in a Diesel Engine

You will see on the package label whether the oil can be used in a diesel engine. According to the API standard, the «C» and «S» symbols are indicators of the kind of engine it is used for. «C» means it is for diesel engines. «S» means it is for gasoline engines. There is also a universal oil type, indicated by certification as S/C.

Depending on the purpose and approval for use, there may be such markings:

LabelApplication
CD+has increased resistance to oxidation, thickening, increased protection of the valve mechanism against wear
CFfor engines with a distributed injection operating on fuel with a sulfur content of more than 0.5%
CF-4for 4-stroke engines with turbo-charging or without it installed on powerful mainline tractors. It has a lower consumption on depreciation and a tendency to carbon deposition. It meets the higher requirements on the exhaust emission
CG4for 4-stroke diesel engines that use fuel with sulfur content less than 0.5%. Suppresses formation of deposits on pistons, wear, oxidation and soot formation. Oil life will strongly depend on the quality of fuel used
CH4for high-speed 4-stroke diesel engines when using fuel with high sulfur content (>0.5%)
CI4for high-speed 4-stroke diesel engines manufactured after 2002 with exhaust gas recirculation. For use with low-sulfur fuels (<0.5%)
CJ-4for four stroke high speed diesels manufactured after 2010
CD-11 or CF-2for two-stroke diesel engines

Unlike with the API, at the ACEA each category has its own meaning. ACEA diesel engine oil is defined as follows:

LabelApplication
B1-96Designed for non-turbocharged units
B2-96 and B3-96Intended for units of automobiles with or without turbocharging
B4-98Oils for direct injection diesel engines requiring special oils

Diesel engines with diesel particulate filters:

LabelApplication
C1for low SAPS oil with reduced HTHS viscosity ≥ 2.9 mPa·s, low viscosity, performance as with A5/B5, with little higher proportions of sulfate ash, phosphorous, sulfur compared to C1
C2
C3for low SAPS oil with high HTHS viscosity ≥ 3.5 mPa·s, low viscosity, performance as with A3/B4, little higher proportions of sulfate ash, phosphorous, sulfur compared to C1
C4
C5for mid-SAPS oil with lower HTHS 2.6 – 2.9 mPa·s, low viscosity, for better and more optimal fuel economy, for vehicles with modern exhaust gas treatment systems, only for engines that meet the appropriate specifications

Commercial diesel vehicles:

LabelApplication
E1-96, E2-96 and E3-96for trucks with highly supercharged engines
E4based on MB 228.5, for an extended oil change, suitable for Euro 3 engines
E5category is included in ACEA E7
E6for EGR engines with/without diesel particulate filters (DPF) and SCR-NOX motors. It is recommended for engines with DPF combined with sulfur-free fuel. Sulfate ash content max. 1%
E7for vehicles without diesel particulate filters (DPF) of the most EGR engines and most SCR-NOX engines. Sulfate ash content max. 2 %
E9for vehicles with/without diesel particulate filters (DPF) of the most EGR engines and the most SCR-NOX engines. Recommended for engines with diesel particulate filters combined with sulfur-free fuel. Sulfate ash content max. 1%

When selecting an oil viscosity, consider the regional operating temperature conditions. The viscosity value directly affects how easily the oil can be pumped through ducts and system components. In addition, the oil viscosity affects the speed of its delivery to the rubbing working pairs in the engine, the battery charge consumption, as well as the mechanical resistance of the crankshaft by the starter when starting in cold conditions. Therefore, for diesel engines, the most commonly used viscosity grades are 5W (down to -25°C), 10W (down to -20°C), and more rarely 15W (down to -15°C). Accordingly, the lower the number before the letter W, the less viscous oil will be.

Energy-saving oils are of low viscosity. They create a small protective film on the surface of the metal, but at the same time save energy and fuel to produce it. However, such oils should only be used with specific engines (they must have narrow oil passages).

If the engine has problems with the cylinder-piston group, compression, as well as poor starting «at cold», it is better to buy oil for the diesel engine, which has a lower viscosity.

What is the best oil for a turbo diesel?

The operation of a turbocharged diesel engine is different from a normal one with higher operating temperatures and faster wear. Therefore, oil for a turbocharged diesel engine must have higher protection and performance properties. However, the recommendations for selection are the same as for any other oil — follow the automaker's recommendations.

ACEA standard B3 for Renault-Nissan turbocharged diesel engines

For turbocharged diesels manufactured after 2004 that have a particulate filter, the ACEA standard is to use:

  • Mitsubishi and Mazda recommend B1 oils;
  • Toyota (Lexus), Honda (Acura), Fiat, Citroen, Peugeot — B2 oils;
  • Renault-Nissan — B3 and B4 oils.

For approvals of other automakers, refer to such recommendations:

  • Ford recommends M2C913C engine oil for turbodiesels from 2004 and later that have a particulate filter.
  • Volkswagen (as well as Skoda and Seat, being a part of concern) singles out even the brand of motor oil VW 507 00 Castrol for turbo diesel engines of its concern, which were produced before 2004 and have a particulate filter.
  • For cars manufactured by General Motors Corporation (Opel, Chevrolet, and others), turbocharged diesel engines produced after 2004 with a particulate filter, it is recommended to use Dexos 2 engine oil.
  • For turbocharged diesel engines produced before 2004 and equipped with a particulate filter, the recommended oil is BMW Longlife-04.

Low SAPS

  • If your modern turbo diesel car is equipped with a diesel particulate filter (DPF), it is better to use a low SAPS oil.
  • SAPS means «sulfated ash, phosphorus, sulfur» and is often called low ash oil.
  • In Europe, according to ACEA, low ash oils are labeled C1 (0.5% ash), C2 (0.8% ash — better use for high performance motors) and C3. In America, there is CJ-4.
  • So an engine oil 5W30 C1, C2 or C3 is a 5w30 grade oil used for vehicles equipped with a DPF. If your vehicle is equipped with a DPF, be sure to check which specification is required — C1, C2, or C3.

HTHS- High Temperature High Shear Rate viscosity, DPF- diesel particulate filter, KAT- catalytic system, SAPS- Sulfated Ash Phosphorous Sulfur. Reduced HTHS- These oils may only be usedin engines that are configured for them.

Remember that a turbocharged car needs an occasional drive with a good load, so that the turbine and the oil in it do not «stagnate». So don't forget to not only use the «right» oil, but also drive the car the right way.

What diesel oil to choose?

If you want to choose the oil for your diesel which has the longest oil life, look at the Total Base Number (TBN). This measures the amount of active anti-corrosive additives in an oil and tells you how prone those additives are to scaling. The higher the number, the greater the oil's ability to neutralize acid and corrosive products formed during oxidation. For diesel engines TBN is within 11...14 units.

The second important number that characterizes oil is total acid number (TAN). It characterizes the presence of products in oil, provoking an increase in corrosion and intensity of wear of different friction pairs in the engine of a car.

As the engine, and therefore the oil, is used, the alkali number decreases and the acid number increases. Therefore the oil at a certain mileage (the average resource of 10 000 miles) the oil has completely exhausted its resource, and further its operation only ruins the engine.

The graph below shows the test results of four types of oil with different acid and alkali numbers.

As can be seen from the graph, the test results were as follows:

  • A oil — 5W30 (TBN 6,5) — was completely worked out after 7000 km;
  • B oil — 5W30 (TBN 9,3) — fully used after 11500 km;
  • C oil — 10W30 (TBN 12) — fully used after 18,000 km;
  • D oil — 5W30 (TBN 9,2) — completely used up after 11500 km.

That is, the oil for heavily loaded diesel engines turned out to be the most resistant one.

What conclusions can be drawn from the above information?

  1. A high value of alkaline number (TBN) is critical for those regions where diesel fuel of poor quality is sold (in particular, with high S admixtures). Using such an oil will give you a longer and safer engine life.
  2. If you are sure of the quality of fuel you use, you have to use an oil with TBN value in the 11...12 range.
  3. Similar considerations are true for petrol engines. Better to use oils with TBN = 8...10. This will give you a chance to change oil less often. If you use oil with TBN = 6...7, in this case be ready to change fluids more often.

Summary

Diesel engine oil has more stable operating and performance characteristics than gasoline engine oil. When choosing an oil, you should always monitor the compliance of the parameters and tolerances of the oil with the requirements declared by the car manufacturer. It concerns both ordinary diesel engines and turbocharged units. try to pour oil with TBN = 9...12, as a rule, this value is specified next to the ACEA standard.

FAQ:

  • Do diesel engines need specific oil?

    You need to use high visconcity oil or synthetic oil, because a diesel engine has a higher combustion ratio than a gasoline motor.

  • What is the difference between regular motor oil and diesel motor oil?

    The main difference between diesel oils is that they have stronger antioxidant and lubricating characteristics.

  • What happens if you put wrong oil in diesel engine?

    Using the wrong oil will cause leaks, or a burning odor to appear while driving. If the oil is not properly selected, engine parts may not lubricate properly and cause friction, which can lead to oil burnout.

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