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You may find The difference between petroleum and synthetic based oils interesting and why synthetic is so superior.

Even though petroleum refining is an advanced science, small amounts of contaminants, such as sulfur and reactive hydrocarbons cannot be completely removed from petroleum, and end up in motor oil base stocks. Synthetics base stock are designed in a lab and therefore do not contain these contaminants. So right from the start petroleum oil is contaminated.

Petroleum oil molecules are of varying sizes. So, as a petroleum oil heats up, the smaller molecules begin to burn off. Deposits and sludge are left behind to coat the inside of your engine. In addition, as smaller particles burn off, the larger, heavier molecules are all that is left to protect the engine. Unfortunately, these larger particles do not flow nearly as well and tend to blanket the components of your engine which only exacerbates the heat problem as friction builds-up. Synthetic oils, on the other hand, because they are not purified, but rather designed within a lab for lubrication purposes, are comprised of molecules of uniform size and shape. Therefore, even if a synthetic oil does burn a little, the remaining oil has the same chemical characteristics that it had before the burn off. There are no smaller molecules to burn-off and no heavier molecules to leave behind. Bottom line is synthetics contain almost no contaminants compared to petroleum oils since they are not a refined product. As a result, if oil burn-off does occur, there are few, if any, contaminants left behind to leave sludge and deposits on engine surfaces.

Petroleum oils also contain paraffins (wax), they tend to thicken up considerably in cold temperatures. Additives are used to help keep the oil from thickening too much due to these waxy contaminants. Synthetic oils, on the other hand, contain no paraffins. Therefore, they need no additive to help with cold temperature operation. Moreover, even without the additives, synthetics flow at far lower temperatures than petroleum oils. Remember additives cause contamination!

Since synthetics contain no additives to aid with cold temperature flow, synthetics maintain their cold temperature flow characteristics for a long period of time. Additive depletion is not a factor in the cold temperature flow of synthetic oils. Synthetics do not thicken due to burn-off. So, this is not a factor in cold temperature flow either. Of course, the obvious result is that you don't need to change synthetic oil as often to regain adequate cold temperature flow.

Water causes acids to be created within the oil and corrosion will begin within your engine. So, there are additives in the oil which are designed to combat these acids. Synthetics contain higher quality and a higher quantity of these additives in order to properly neutralize these acids for a longer period of time. These additives do deplete over time, but it takes longer with synthetic oils than with petroleum oils.

Here's a couple important facts; Additives are also used to keep oil contamination in check and to keep it from damaging your engine. These additives keep potentially wear causing contaminants suspended and contained in your oil so they don't cause excessive wear or deposit build-up within your engine before your filter can remove them. Synthetics have higher additive treat rates than petroleum oils (in addition to using higher quality, more expensive additives), so they can perform this contaminant control function for a much longer period of time than a petroleum oil can.

To control acids the Total Base Number (TBN) describes the acid neutralization ability of an oil, with higher TBN oils providing longer lasting acid neutralization. Synthetics nearly always have higher TBN values than petroleum oils do. The result: longer and better acid neutralization capability allowing for extended drain use.

Every single aspect (which there are many) of what oil provides for your engine is better in synthetic oil, including how long you can use the oil before contamination is a problem. The most important difference is the pour rate. This one aspect is the biggest contributor to engine ware. This is how long it takes the oil to reach vital parts of the engine during start-up (especially when cold). You wouldn’t believe the difference between dino and synthetic. The same difference in this one aspect is typical of ALL the other aspects in dino and synthetic.

Koz