How often should you change the oil

Many car owners don't know how often you should change the engine oil of their car, or doubt the information provided by the manufacturer regarding the frequency of consumables replacement. And not for nothing. It is often not quite right to change it every 10-15 thousand kilometers.

It is better to be guided by the number of worked hours and the average speed. The answer to the question of how often to change the oil in the engine has many components. Among them — are the car producer's recommendations, vehicle operating conditions (heavy/light, in the city/highway, often/often used), mileage before oil change and total mileage, the technical condition of the car and used oil. Also, additional factors affect the frequency of oil changes in the engine — the number of engine hours, engine power and volume, the time since the last oil change (even without taking into account the operation of the machine).

For those who don't want to go into details and understand everything in detail, let's give an answer to the replacement interval: in urban conditions oil «works» 8-12 thousand, on the highway / light traffic mode without traffic jams works up to 15 thousand km. Only the laboratory analysis of oil drainage can give the most exact information on when to change it.

What affects the replacement frequency

The interval of changing the engine oil is affected by 10 indicators:

  1. Operating conditions and modes.
  2. Engine displacement.
  3. Brand of previously used oil (synthetic, Semy-Synt, mineral oil).
  4. Classification and type of oil used (API and longlife system).
  5. State of engine oil.
  6. Drainage method.
  7. Total mileage of the engine.
  8. Technical condition of the car.
  9. Type of fuel (gas, gasoline, diesel) and its quality.
  10. Quality of consumables.

The manufacturer's prescriptions are not included in this list, since for him the service interval is a marketing concept.

Modes of operation

First of all, the timing of oil replacement in the engine is influenced by the operation of the vehicle. Without penetrating into the essence of different transitions, it is necessary to mention two basic modes — on a freeway and in a city. The fact is that when the car drives on the highway, firstly, the kilometrage runs much faster, and secondly, there is a normal cooling of the engine. Accordingly, the load on the engine and the oil used in it is not so high. On the contrary, if the car is used in the city, its mileage will be much lower, and the load on the engine will be higher due to the fact that it often stands at traffic lights and traffic jams with the motor on. In this case, the cooling will be insufficient.

In this connection, it would be more competent to calculate how often you have to change the oil in the engine, based on engine hours, as it is done in the truck, agricultural and water equipment. Here is an example. 10 thousand kilometers in city conditions (with an average speed of 20-25 km/h) the car will run for 400-500 motor-hours. And the same 10 thousand km on the freeway at the speed of 100 km/h — only for 100 motor-hours. The more so, that conditions of engine and oil operation on the freeway are much milder.

Driving in conditions of a megapolis is fairly equal to driving on a hard off-road in the question of how it ruins the oil. This is especially true when its level in the crankcase is below average, and even worse when it is less than the minimum level. Also remember that in summer in hot weather the oil is much more stressed due to the high temperature, including from the red-hot road surface.

What affects the frequency of oil changes

Engine displacement and type

The more powerful the engine, the easier it is for it to survive load changes as well as difficult operating conditions. Consequently, the oil will not be affected as much. For a powerful engine, the movement on the highway at a speed of 100-130 km / h is not a significant load, it will be below average. As the speed increases, the load on the engine, and therefore on the oil, will change smoothly.

In a small engine, the transmission is designed for a small speed range, and operating speed range. Therefore, it experiences higher loads in critical modes than high-powered ones. When the load on the engine increases, so does the temperature of its pistons and the amount of crankcase gases. This leads to a general increase in temperature, including oil temperature. Small forced engines (e.g. 1.2 TSI and others) especially have a hard time. In this case, the turbocharger also adds to the load.

Additional factors

Theese include high operating temperatures, poor engine crankcase ventilation (especially in urban driving), use of poor-quality or unsuitable oil for the engine, dirt in the oil ducts, clogged oil filter, the operating temperature range of the oil.

It is believed that the optimum interval of oil changes in the engine is 200 to 400 engine hours under various operating conditions, with the exception of maximum load, including driving at maximum speed and maximum speed.

Also of great importance is the type of oil used — mineral, semi-synthetic or fully synthetic. Each has its own recommendations for the duration of the operation.

Recommendations for engine oil changes

To the recommendations of car manufacturers should be treated very skeptically. Not completely ignore them, but make your own adjustments. If you drive a car only in urban conditions (according to statistics, the majority of such car owners), it means that the oil is operated in a heavy mode. Remember, the less oil in the crankcase, the faster it ages.

Change your oil at least once a year, whether or not you run your car. In either case, the oil in your engine has a shelf life of six months to a year maximum.

It is more correct to calculate oil change intervals by moto-hours. However, the difficulty of this methodology is that it is sometimes difficult to convert kilometers into moto-hours, and based on this information get an answer.

Let's take a closer look at two methods, which allow you to calculate empirically, but quite accurately, how often to change synthetic (and not only) oil in the engine. To do this, your car must have ECU, which shows the average speed and fuel consumption for the last at least one thousand miles (the more mileage, the more accurate the calculations will be).

The first method (speed calculation)

For the calculations, you need to know the average speed of your car over the last few thousand kilometers and the automaker's recommendations at which mileage you need to change the oil. For example, the mileage before the oil change is 15 thousand kilometers, and the average city speed is 29.5 km/h.

Accordingly, to calculate the number of engine hours, you need to divide the distance by the speed. In our case it will be 15000 / 29,5 = 508 engine hours. So, it turns out, in order to replace the oil under these conditions, you need to use a lubricant with a life of 508 moto-hours. But in reality, such oils simply do not exist at the moment.

We offer you the table with types of engine oils and their corresponding values of engine hours according to API (American Petroleum Institute):

Table of oil correspondence to motor hours
Type of oilResource number of motor hours
Synthetic oils
API SM/SN300-350

Let's assume that a car engine is filled with SM/SN grade oil, which has a service life of 350 engine hours. To calculate the mileage, multiply 350 engine hours by an average speed of 29.5 km/h. The result is 10,325 kilometers. As you can see, this mileage is strikingly different from the one offered by the automaker. And if the average speed will be 21.5 km/h (which is more typical for large metropolitan areas, taking into account traffic jams and downtime), then with the same 350 motor-hours, we get 7525 km of run! Now it clearly becomes clear why it is necessary to divide the recommended car manufacturer mileage in 1.5-2 times.

The second method of calculation (based on the amount of fuel consumed)

As the initial data, you need to know how much fuel in the data sheet your car spends per 100 km of way, as well as this actual value. It can be taken from the same ECU. Suppose that the car on the passport «takes» 8 liters / 100 km, and in fact — 10.6 liters / 100 km. Mileage for replacement remains the same — 15000 km. Let's derive the proportion and find out how much theoretically machine should spend to overcome 15000 km: 15000 km * 8 liters / 100 km = 1200 liters. Now make a similar calculation for the actual data: 15000 * 10.6 / 100 = 1590 liters.

Now we need to calculate at what distance is necessary to carry out the actual oil change (ie, how much the car will travel on the theoretical 1200 liters of fuel). Let's use a similar proportion: 1200 liters * 15000 km / 1590 liters = 11320 km.

Here is an electronic calculator which allows you to calculate the value of actual mileage before oil change, using the following data: theoretical fuel consumption per 100 km, actual fuel consumption per 100 km, theoretical distance to oil change in kilometers.

In many modern vehicles, the ECU constantly monitors how many miles to change the oil in the engine. This recommendation is based on actual data — average engine RPM, oil and engine temperature, number of cold starts, speeds, and so on. In addition, the program takes into account errors and technical tolerances. Therefore, the computer reports only approximately.

However the simplest and the most effective method of check is a visual inspection of oil condition. For this purpose do not be lazy to open the hood from time to time and check if the oil is not thickened and burnt. Its condition can be estimated visually, including the drop method. If you saw that the oil is dripping from the dipstick like water, it is a sure sign that the oil is worth replacing.

Another interesting method of checking is by spreading the composition on a cloth. Very liquid oil will form a large and liquid slick that will tell you it's time to change the fluid. If this is the case, go to a car service right away or do the procedure yourself.

How often should I change the oil in a diesel engine?

As for diesel engines, the same calculation logic applies here as for gasoline engines, but do not forget that the oil in such an engine is subjected to even greater exposure to external factors. Therefore, it is necessary to change the oil in a diesel engine a little bit more often.

The motorists recommend to automobile owners of diesels to change oil in every 7 — 10 thousand kilometers of run, depending on the car and the oil used.

In order for the oil in a diesel engine to work longer it is necessary to select it correctly. It's worth selecting both according to permissions and value of total base number (TBN) and acid number (TAN).

Why do we need regular oil changes?

What can happen to your car if you don't change the oil in the engine for a long time? During the operation of a car, and even when it is parked, there is a continual chemical breakdown of the additives. Naturally, this process is carried out faster when driving. Natural deposits form on the engine crankcase, oxidation processes occur with the individual constituents of the oil, its viscosity and even the pH level of the oil changes. These facts are the answers to the question — why change your oil at least once a year.

Some car manufacturers and engine oil manufacturers indicate how often you should change the oil in the engine, not by mileage, but by frequency, usually by months.

And under considerable load, the described processes in the oil occur at an even greater rate. Especially at high temperatures. But modern manufacturers are constantly improving the technology and chemical composition of their oils. Therefore, they are able to withstand contamination and high temperatures for a long time.

Here are some interesting factual data that was obtained experimentally. They will help you decide after what mileage to change the oil in the engine.

What does the oil test show?

As a result of testing several types of synthetic oils in urban traffic (work at idling speed at 800 rpm for 120 hours, as an analogue of the work of 10 thousand kilometers of mileage on the highway) obtained interesting facts.

The viscosity of all engine oils during prolonged idling up to a certain (critical) moment is significantly lower than when driving «on the highway». The value of engine oil viscosity drop is about 0.4-0.6 cSt (centistokes). This value is within 5-6% of the average level.

Approximately at 70-100 engine hours (every oil has different but the tendency is the same for all of them) viscosity starts to increase sharply. And it is much faster than in «highway» mode. It happens so because of the constant contact with the products of incomplete combustion (having acidity) and reaches its critical saturation.

The widespread opinion that a large amount of dirt is formed in the engine in idle mode has not been experimentally confirmed. However, the amount of high-temperature deposits was low and the amount of low-temperature deposits was high.

As for the wear products, the amount of them is much higher in the oil operated in the «plug» mode than in the one on the «track». The reason for this is the low speed of the pistons, and the high operating temperature of the oil (no ventilation). As far as the burnout is concerned, every oil behaves differently. However, it can be argued that due to high operating temperatures and increased thickness, so will the loss.

Causes and consequences of untimely change of engine oil:

  • Formation of deposits. The causes of this phenomenon lie in the process of destruction of additives or oil contamination by combustion products in the engine crankcase. The consequences are a significant reduction in engine power, an increase in the content of toxic substances in the exhaust gases, their blackening.
  • Significant engine wear. Causes — oils lose their properties due to changes in the composition of additives.
  • Increase of oil viscosity. This can occur due to the same reasons. In particular, due to oxidation or violation of additives polymerization due to improper oil selection. Problems resulting from this include difficulties in oil circulation, considerable wear and tear of the engine and its individual components. Oil starvation of engine may cause difficulties with starting the engine when cold, in critical cases even engine failure is possible.
  • Rotation of crank pins. It occurs due to clogging of oil channel with thickened compound. The smaller is its cross-sectional area, the greater is the load on the crank pin bearings. This causes them to overheat and rotate.
  • Significant wear of the turbocharger (if any). In particular, the risk of rotor damage is high. It occurs due to the fact that the used oil has a significant impact on the compressor shaft and bearings. As a consequence, they are damaged and scratched. In addition, dirty oil clogs the compressor's lubrication passages, which can cause the compressor to jam.
Do not operate the machine with burnt or thickened oil. This will expose the engine to considerable wear and tear.

The problems described above are characteristic of machines operated in urban conditions. After all, it is considered one of the most difficult for the engine.


Each car owner must decide for himself how often to change the oil in the engine. This should be done taking into account individual circumstances. We recommend that you use the methods of calculation by moto-hours and gasoline consumption, given above (including calculators). In addition, always visually assess the condition of the oil in the engine crankcase. This way you will significantly reduce the wear and tear on your car's engine, which will save you from having to make costly repairs. Also, when replacing, buy quality oils recommended by the manufacturer.


  • How often should you really change your oil?

    Despite the fact that a lot of car owners change oil every 5000 kilometers, the acceptable interval is from 8000 to 12000 kilometers.

  • Is it OK to change oil every 2 years?

    It's better to change the engine oil once in 1 year. But if you don't use your vehicle frequently, you can change lubricant every 2 years.

  • How can you tell if you need an oil change?

    You should change oil, if you've mentioned several signs:

    • “Oil change” or “Check Engine” light came on.
    • Your engine oil is dirty.
    • You smell oil inside the car.
    • Engine produces loud knocking and noise.
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