How to calculate oil replacement frequency based on the actual fuel consumption rate

Under current conditions of urban car operation, oil replacement frequency should be carried out not on the recommendations of the manufacturer, but on the basis of fuel consumption rate and quality of oil. You can travel about 30 kilometers not for half an hour, but for about two or more hours (because of traffic jams). All this time, the fuel is consumed, because the engine is running, and consequently, the oil is consumed as well. Auto manufacturers give the average values. That is, it is assumed that from replacement to replacement a car drives in the conditions of the route not less than 70% of the trips with an average fuel consumption and nominal crankshaft speed. Of course, it is impossible, and we need a more thorough method for calculating the engine oil resource.

How to calculate the oil resource

Experienced drivers offer two more or less accurate formulas for calculating the mileage before the oil replacement. The first formula is similar to that used by some German, American and Japanese auto manufacturers and is based on engine hours. The second formula is based on fuel consumption rate. As a rule, the difference between their results is not more than 1000 km, which is quite acceptable, given the mileage stated by the manufacturer.

Since more expensive cars often have the hour meter and, accordingly, a hint on the on-board computer display that it is time to replace oil, we will help the owners of low-cost cars, which often have no such meter, by providing a calculator for the oil replacement frequency based on the actual fuel consumption rate.

The calculator will help everyone to calculate oil resource, and when it is better to replace it. To verify the accuracy of these calculations, you can check the data given on the dash display (if any) or calculate the engine oil resource in engine hours, using the appropriate formula. Calculation procedure is as follows:

The mileage recommended by the manufacturer should be divided by the average travel speed (in urban settings and along the route). So you will know the number of engine hours during which the engine should run before oil replacement.
Calculate the average value between the speed along the route and the speed in the city.
Take the average number of engine hours and multiply them by the average speed. So you will get the required distance.

Engine oil resource

Having an average number of engine hours, it is easy to see whether the oil you fill in can be used for the period indicated by the auto manufacturer, since many oil manufacturers indicate how many hours it should work on the packaging. As a rule, the trend is as follows:

Petroleum oil — about 150 h;
Semi-synthetic oil — not more than 250 h;
Synthetic oil with API SM/SN — up to 350 h;
LongLife oils — at least 400 h.

In this case you should also take into account that engines with a large volume require more oil, and consequently, its load is smaller. In fact, each engine has an individual interval, and it depends on the operating conditions.

How online calculator calculates oil change frequency

Our online calculator for oil change frequency based on fuel consumption rate is the easiest way to find out the correct interval, without going into details such as the number of engine hours and the average travel speed. No matter how you drive or stand at idle, the fuel is still consumed by the engine and its consumption rate is far from the one specified by the manufacturer. In addition, the wear trend influences the oil life. The basis of the calculation result is the ratio between the estimated and actual oil burning under specific operating conditions.

How to calculate oil change frequency using the calculator

To calculate the practical mileage before oil change based on fuel consumption rate, enter three values in the appropriate fields, i.e. the recommended mileage before the replacement (as a rule, this value is 10...15 thousand kilometers), the certified value of fuel consumption per 100 km (just as the mileage, it is specified in the car maintenance manual), and the actual average fuel consumption rate per 100 km, which is displayed on the dashboard of any injection or diesel car. To get the result, click on the «Calculate» button.

As a result, you will get an answer to the question about the interval of engine oil replacement. It is obtained on the basis of actual data on the amount of fuel used, which the auto manufacturer specifies, relying on the ideal operating conditions, thereby assuming the life of high-quality engine oil under severe conditions, when a car operates in various modes (especially relevant in cold weather and under urban conditions).

FAQ

How often should I change mineral oil?

Mineral oil must be changed at least every 5000 km. If the reference how often to change the mineral engine oil is made by moto-hours, which is more fair, you should be guided by 150 moto-hours. However, this figure may vary, as well as the total mileage, because it depends on the crankshaft rotation speed.
How often should I change semi-synthetic motor oil?

There are no long-living semi-synthetic oils, the additives in such grease do not hold for a long time, and the viscosity changes strongly with the time, so the decay products pollute the engine. The maximum frequency of replacement is about 10,000 km. But if operating conditions will be a little more complicated or there will be a higher number of motor-hours (for semi-synthetics — their number should not exceed 250), it is better to shorten this interval to 8,000 km.
How often should I change synthetic motor oil?

Synthetic oils allow to get a mileage from replacement to replacement up to 30 thousand kilometers in light conditions, but at the real operation of the engine city / highway 50/50, it will go no more than 15 thousand km. However, how often to change the synthetic oil and grease of another class depends on the quality of fuel, operating conditions, driving style, frequency of use of the car. Therefore, the recommended frequency is at least 12,000 km. In engine hours it will work about 300 for such mileage, which is close to the maximum life of most conventional synthetic oils.
When should you change LongLife Oil?

The Longlife designation indicates that the oil is rated for the flexible service intervals recommended by the carmakers. The maximum replacement interval for LongLife motor oil is 25,000-30,000 km, or every 2 years of operation. Under extreme engine operating conditions such oil with extended drain interval shall be changed twice as often. Thus, in countries with insufficient fuel quality and under heavy loads, Long Life oils have 15,000 km (about 400 motor-hours) interval of service.