The first rule to use in this situation – any better engine oil than its absence.
The risk that the additives of different types will enter into a chemical reaction that can destroy the rubber seals, lead to the development of corrosion and coking, will be the harder, the greater the number of “foreign” oil may be topped up.
As a rule, if refill is not large, we can make it 10% safe.
However, what if the choice of oils in the store or the service station is still not so bad, but the product is exactly the specification that you have used previously that are not represented? In this case you need to try to discover oil, the same manufacturer that was previously poured into the Assembly of your car.
The fact that different cars of the same brand have the General common elements and similar additives unlike products of other brands. It is clear that it is possible, you should pour synthetics in synthetics, semi-synthetics in semi-synthetics, and mineral water in the mineral water.
Requirements of the same viscosity is at least to neglect, especially if the dose is topping small. For example, it is possible to prevent mixing oils 5W30 mobil and mobil 10w4.
Also advised to know the standards (indexes) API (American) and ACEA (European). Each of these standards under the most understand the mixing of oils from different companies, so chances are high that the threat to the power plant of chemical reactions (precipitation, effect foaming, etc.) will not.
There are other useful rules, which are designed to help protect the unit during emergency topping up of lubricants. Thus, the class of oil that you use for the topping should match with the one already in the motor. Namely, not to add inside the “cars” oil, which is used in trucks.
Possible mix oils of the same viscosity. You should also try to improve the quality of oil – mineral add the semi-synthetics, in semi-synthetics – synthetics. On the contrary (to lower the quality of the oil), it is not necessary.
It is clear that topping the substandard motor oil, you need to get to the repair site, followed by washing of the engine and a complete replacement of the lubricant recommended by the vehicle manufacturer.