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Common Synthetic Car Engine Oil Myths

Find out some actual Facts about synthetic car engine oil from experts in the automotive lubrication field.

Synthetic Car Engine Oil has so much incorrect information and myths surrounding it it's hard to know what's true, cut through all the nonsense and read some actual facts below.

Common Synthetic Oil Myths

There is a lot of information on the internet about oils, but a lot of it is wrong or based on out of date information.

Synthetic motor oils damage seals

Complete Nonsense! Any oil seals made after 1975 or thereabouts will be entirely compatible with any type of synthetic engine oil. (The same goes for synthetic gear oils and transmission oil seals.) It must be understood that everything associated with lubrication is thoroughly tested. The major oil manufacturers do not make oils that attack seals; seal manufacturers ensure that their products function correctly with modern lubricants.

Synthetic oils are too thin

It is true that the best synthetic blends can be low viscosity (0w-20 for example), but they do not have to be! It is also true that the latest engines are designed to run on thin oil, which improves power output and fuel consumption. Even so, thicker synthetic based grades (10w-50, 15w-50, 20w-50etc) are available for air-cooled motors, older engines, or severe high temperature conditions. These grades can also benefit rebuilt classic engines dating back to the 1940s

Synthetics mean higher oil usage

The complete opposite of the truth. Oil consumption in well-maintained modern engines is mainly down to the oil evaporating at high temperatures. Synthetic base oils (specially the PAO and ester types) are very resistant to evaporation loss even in low viscosity blends, so oil consumption is minimised. Obviously, engines with worn valve guides, defective seals and worn piston rings will use oil regardless, so there is no point in using expensive synthetics as an ‘old banger lube’.

Synthetic oils are not compatible with other oils

All engine oils intended for normal road use in recent 4-stroke engines are compatible with one another, regardless of the base make-up. (mineral, PAO/ester/hydrocracked synthetic, and semisynthetic.) There is no need to flush or strip down an engine when changing from one type to another. (...but be careful with the exceptions of castor oil based racing oils and plant based engine oils.

Synthetic oils produce sludge

Well honestly, this is just totally daft. All synthetic bases are more resistant to oxidation than mineral oil, and sludge is largely due to oxidation. In any case, all motor oils intended for road use meet the higher API specs such as SH, SJ, SL and diesel equivalents. One of the main reasons for introducing the API specs back in the 1950s was to deal with oil sludge problems. All high-spec oils run very clean, especially synthetics.

Synthetic oils cannot be used with catalytic converters

‘Cats’ will perform more efficiently and last longer if synthetic based engine oil is used. Their lower volatility means that less oil reaches the combustion chambers via crankcase ventilation, so there are less harmful ash residues from burnt oil to de-activate the catalyst matrix.

Synthetic oils can void warranties

People who make statements such as this never define the type of synthetic, thus revealing their ignorance. Provided that an oil meets or exceeds the API and viscosity ranges specified in the handbook or manufacturers own specification if given, the warranty will not be affected. (By law, OEMs cannot insist that a particular brand of oil must be used to maintain warranty.)

Synthetic oils will last forever

The better synthetic blends will certainly last longer*, especially in high performance or high annual mileage situations, but ‘forever’ is not on, simply because contaminants such as soot, and acid gasses from traces of sulphur in the fuel degrade the oil.

*Provided that a very shear resistant VI improver polymer is used in the oil formulation to keep the viscosity up to spec. This point is often forgotten.

Synthetic oils are too expensive

True, for older vehicles that use a lot of oil or are almost ready for the scrap yard. For cars that are worth maintaining, the right types of synthetic oil are a cost-effective way of retaining ‘as new’ performance, low fuel consumption, and reducing maintenance costs.

Shop for Semi / Part Synthetic Care engine oil or Fully Synthetic Car Engine Oil.

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