Repsol;
- Can two lubricants be mixed in the same engine?
All lubricants on the market (whether petrol or diesel engines, mineral or synthetic) can be intermixed. Nonetheless, mixing two different quality oils reduces the overall quality.
- What is the difference between a synthetic and a mineral lubricant?
A mineral lubricant is made up of a base obtained directly from oil distillation plus some additives which improve its performance.
With a synthetic lubricant, the bases are treated through a physical/chemical process in order to obtain a higher quality and performance. With semi-synthetic lubricants, mineral and synthetic are combined.
- Are synthetic lubricants the best?
Yes. Synthetic lubricants have been specially created to respond to the demands of the engine or to be used in extreme temperatures and very intense service conditions.•
Castrol;
Can I switch between a synthetic and a conventional oil?
It is a common myth that you cannot go back to a conventional motor oil after using a synthetic. All of Castrol's oils are fully compatible with one another, and there is no cause for concern if you choose to switch from conventional to synthetic or vice versa. Another common myth is that you cannot switch from a conventional oil to a synthetic oil without first flushing your engine. If you currently use conventional oil, you do not have to flush your engine before you switch to Castrol SYNTEC.
Valvoline;The Aging Standard
Conventional motor oil has been the benchmark in engine lubrication since Carl Benz invented the car in the late 1800s. Over the years, oil manufacturers have improved the refining processes to remove impurities. Still, mineral-based oil, even in its most pure form, remains somewhat imperfect.
This liquid lubricant performs two primary functions inside your engine. It reduces friction between moving parts, and it dissipates heat created by the combustion process. At normal operating temperatures, conventional oil protects the internal workings of your engine. This ability to protect as well, however, when engine temperatures rise or fall below the norm (as you would find upon start up, during spirited driving or in extreme climates) is limited because at lower temperatures conventional oil becomes thick, or more viscous. (NOTE,vicous=thick,Tig) In this state it may have difficulty reaching critical components. At higher temperatures, the same oil often becomes too thin to adequately coat and effectively protect moving parts.
Synthetic oil, on the other hand, has a higher tolerance for temperature extremes, thereby maintaining a more consistent viscosity. This means your engine is better protected overall regardless of engine operating temperatures.
Size Does Matter
Synthetic oil is also more resistant to thermal and oxidative breakdown, processes that occur when oil is exposed to the severe conditions inside an engine. When motor oil begins to break down, it is essentially burned away, which causes it to lose its ability to protect valuable engine parts and dissipate heat.
The reason for synthetic oil's increased resilience stems from its uniform molecular structure. Conventional base oil is composed of several sizes and shapes of hydrocarbon molecules. This variation brings with it a range of evaporation, oxygenation, and burn points. Included in the mixture are some comparatively unstable molecules, some of which break down very soon after the conventional oil is poured into your car. This forces the remaining oil to work harder.
To overcome the problem of thermal and oxidative breakdown, synthetic base oils are created through a series of chemical synthesis. The starting materials may be a mixture of relatively pure small molecules. In this case the small molecules are combined to make new, larger molecules. Alternatively the starting material may be a broad mixture of larger molecules. In this case the large molecules are broken down and rearranged. The result is motor oil that is composed solely of pre-selected similarly sized molecules devoid of any weak links that inhibit performance. The new molecules are specifically shaped to offer optimum lubrication and maximum resistance to thermal breakdown.
Anyway,that's just a few of the sites I got from a google search.
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