Esters are an aromatic hydrocarbon group found in many fruits and vegetables. They are commonly used as flavoring agents in drinks, and for their smells in perfumes. Esters are defined by the presence of one carbon atom and two oxygen atoms attached to the end of a hydrocarbon molecule. Since we have already seen by now that not all hydrocarbons perform the same , it can be assumed that not all Esters function the same in terms of engine oil. There are some 600 known Esters, and manufacturers have found that some Esters can be synthesized from natural resources and be very stable in extreme heat and stress, such as in a racing engine. Most Esters help swell and condition seals, and may be used as an additive in other oils for this reason. Esters also have a polar affinity to most metals, and this allows film strength under zero pressure. Some esters, such as polyolesters, are not hydrolytically stable and are not compatible with elastomer type seals. Most Ester based oils will have NOACK scores around 6% for a 30wt oil.
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