Above all, we should clear up what we mean by the word “different”.
If you speak about oil type (mineral/semisynthetic/synthetic), then you certainly should not mix them. These oils are different by their manufacture method, have absolutely different characteristics and therefore should not be mixed.
If you speak about oil characteristics then you should at least add an oil having the same viscosity index (SAE) and performance (API) degree.
Example: If you use engine oil SAE 10W-40 and API SL/CF then the oil that you add must have exactly the same indices!
All the engine oils which are present on the market already have the additives package which is designed to help the engine oil to perform best its functions. The higher the operating characteristics of an engine oil (API degree) the higher the quality of an additive package is and hence the quality of the oil itself.
The use of additives is justified only in case when the positive effect from its use by far outweighs the damage which this additive may incur to an engine.
For example, a viscosity additive put to an engine with low compression may well help you cover thousand miles more before your engine needs to be overhauled. At the expense of oil thickening the gaps between cylinder block and pistons are shrunk, as a result the compression goes up, the oil does not get into combustion chamber, the plentiful smoke discharge from combustion pipe is stopped.
Synthetic engine oil has the following advantages:
We shall not go into details of revealing all the peculiarities of oil manufacture as this does not in the least affect the buyer’s choice. Instead, we shall dwell on advantages and flaws of each of the above-mentioned oils.
The correct oil change interval is specified in the service book of your car. The average interval of engine oil change of a car is 10,000 kilometers (from 8,000 to 15,000 km). There are engine oils, which are changed once per 30,000-40,000 kilometers. Oils of this class are generally used in the engines of modern commercial vehicles. As for the oil change in engines of agricultural and construction equipment, the crucial here is not the mileage- but hour-based maintenance (since the above machines operate without being moved or at low speed). Modern oils can be changed once in 200-500 operating hours.
The modern market offers consumers many sorts of oils under a variety of trademarks which are more or less recognized. Unfortunately, as is the case on other highly competitive markets, the buyer is often confronted with counterfeiting. Mostly, well-established brands are forged which urges manufacturers to regularly update the protection of their brands from counterfeiting. One of the easiest ways to protect yourself from buying fakes, is to purchase products from reliable suppliers.