Why use synthetic or semi-synthetic motor oil?

Answer 1

Synthetic or semi-synthetic motor oil offers longer time periods between oil changes compared to using regular motor oil especially for drivers who might be prone to ignoring their periodic maintenance oil changes.

However it should be noted that a 2-year motor oil test done on 75 New York taxi cabs in 1996 showed no significant nor any discernable differences whatsoever between using regular motor oil with a package of additives versus synthetic motor oil in terms of performance, sludge buildup, and wear and tear. It's an equal tie or in other words it looks to be more of a matter of financial capabilities whether a motorist can afford the overly expensive price of synthetic oil mostly for the peace of mind since apparently synthetic oil is practically no better and no worse than regular motor oil with additives.

Synthetic motor oil is thinner than regular motor oil but withstands high and low temperatures slightly better than regular motor oil and therefore recommended for high performance racing engines or for use in very extreme hot and/or very extreme cold climates. Synthetic oil takes slightly longer to breakdown before losing its lubricating properties which translates into longer time periods between oil changes but it still requires periodic oil changes. Full-synthetic oil is recommended for extreme cold climate start-ups because its thinness makes it less sticky and less tacky between the moving metal parts of a cold engine which makes it easier for cold engines to turn-over compared to using regular motor oil which is a thicker oil but then it's the same reason why 5W(Winter)/40 or higher multi-weight motor oil is recommended for extreme temperature climates rather than choosing 10W/30. But synthetic oil is warned against using during a new engine's break-in period and also warned against using in engines prone to leakage because the thinness of the synthetic oil increases leakage particularly in older engines.

Semi-synthetic motor oil is said to offer many same exact advantages as full-synthetic but at around half the price or so.

Regular motor oil with an additive may be cheaper but it apparently works just as good as the more expensive synthetic oils and not worse nor better but essentially the same in regards to lubricating and protecting engines.

For most motorists but not for all, although synthetic motor oil is better than regular motor oil it's probably not likely worth the overly expensive price tag unless you're into high performance racing or live in very extreme climate temperatures otherwise everything else about full-synthetic motor oil sounds to be pure hype and perhaps possibly the placebo effect or else we would've expected any noticeable degree and/or some kind of significant difference of sludge buildup and/or wear and tear in at least one engine out of the 75 city cabs from a 2-year motor oil test instead of absolute zero difference, wouldn't we?

The motor oil used in the Consumer Report 2-year motor oil test used a full package of additives but no tests were done using just plain motor oil without the additional additives, however, an oil expert strongly advises and warns against using any additives, as well as against flushing, in an article entitled "Motor Oil Myths and Facts", quote: "Do not use any oil additives no matter how much they are hyped on TV. They provide no benefit and can interfere and react with the additives already present in the oil. Some additives have particles that can clog oil passages and clog filters. Common additives that are heavily hyped are Slick 50, Duralube, and Prolong." Unquote.

Indicative of the 1996 2-year test and as of 2009 in comparison to 30 or 20 years ago the quality now-a-days of standard plain motor oil usually already contains its own detergent additives and is improved to where it now appears there's no longer any appreciable difference in the performance or benefit between using either plain regular motor oil without additional packages of additives vs synthetic as long as periodic oil changes are maintained as they all work equally the same and equally well at performing the functions they're designed to do. In other words and hypothetically speaking if a shop mechanic were to perform reasonable periodic oil changes over the next 10 or more years but ended up telling the car owners the mechanic had always been using expensive synthetic oils even though the mechanic had secretly been using cheaper plain motor oil whether with or without additional additives, the owners as well as other mechanics would not be able to detect nor distinguish any difference upon mechanical inspection of the engine parts and would not be able to tell whether synthetic or regular oil had been used.

In conclusion and if money is of no concern then the only lazy advantage to using synthetics versus regular with additives appears to be the longer periods between periodic maintenance oil-changes. I haven't researched any actual 10-year span statistics although I'm only guessing it could perhaps be something like a difference between maybe 2 or 3 synthetic oil-changes versus maybe 4 or 5 regular oil-changes per decade?