Toyota had problems with these engines and thousands of them were replaced under warranty with an engine that had a revised piston design, alleviating the problem. It is possible this was done with your Corolla. If not, sooner or later this problem will rear its ugly head.
With the problems older Toyota's had due to the comparatively poor performing conventional petroleum based motor oils they had been using, I have a very strong suspicion this is now why all new Toyota's come with synthetic oil in their engines right from the Toyota factory assembly lines. Since they started doing this, suddenly the oil problems went away.
No, I would not recommend changing to just any synthetic oil, as most of them on the market today I would
not put in my engine if you paid me. Most of them are not even synthetic oils in the traditional sense of the term, which is a man-made high performance lubricant that comes from a laboratory and is known as a Group IV PAO based synthetic motor oil, that outperforms a conventional petroleum lubricant in every single comparison. It has no petroleum oil in it at all. The vast majority of, "synthetic oils", on the market today are merely conventional petroleum based crude oils, (and all the inherent drawbacks they are saddled with), but merely subjected to a higher degree of refining. They are known as Group III, "synthetic oils". Since so many man-made process are used to manufacture this cheaper, "synthetic oil", in the U.S.A., it can be legally referred to as a, "synthetic oil". I find this very deceptive and abusive of consumers. In Germany, they don't allow these deceptive practices and the lower performing Group III oils are not allowed to be referred to as a synthetic oil. We can all buy a $39 radial tire, or we can buy a higher priced radial tire from Bridgestone, or Michelin and reap all the benefits the better quality radial tires offer. So it goes with synthetic oils too. Wise consumer don't buy a price, they buy a product.
One of the most distinct drawbacks of a conventional petroleum based crude oil pumped from the ground, is that the molecules of this oil are random in size. Some of them are large, some of them are medium and some of them are small. When subjected to the high temperatures found inside a modern day engine, the smaller molecules burn off or evaporate first, which then can create sludge, carbon deposits, varnish and gum inside the engine. This acts as a layer of insulation, reducing the transfer of heat from the engine to the atmosphere, causing engine temperatures to increase, which causes more sludge, further escalating engine temperatures, and so on. It's a vicious circle. Because of this, the oil inside the engine gets thicker and thicker, which reduces lubrication and fuel economy. This is why many motorists have noted that as they put more and more miles on their conventional petroleum lubricated engine, the fuel economy will decrease. Then when they change the oil, (removing the thickened oil), and install new oil, presto, better fuel economy returns. This is not a problem with high quality synthetic motor oils like AMSOIL, as they don't tend to thicken over time.
Conversely, true Group IV PAO based synthetic motor oils like AMSOIL Signature Series have their molecules all the same size, which makes them very resistant to burning off inside a hot engine, greatly reducing or even totally eliminating engine sludge. Another benefit is at the other end of the temperature spectrum, when it gets very cold in the winter. With conventional petroleum oils, the larger molecules along with naturally occurring contaminants like paraffin/waxes that remain in the finished product of a bottle of conventional petroleum oil, congeal, making the oil very thick. This can lead to hard starts during cold winters, reduced lubrication, increased engine wear and reduced fuel economy. Cold room engine start tests have shown that up to 40% of all engine wear occurs during cold winter engine starts while using a conventional petroleum oil. Simply using a high quality synthetic oil will alleviate that problem.
Also, merely because an oil has the, "synthetic oil", label on the oil bottle doesn't mean it is capable of safe extended drain intervals. For a synthetic oil to be safely capable of that, its additive package has to be formulated for the rigors of extended drain service. Up to 25% of a quart of motor oil is made up of its additive package, which are chemicals a tribologist, (an oil chemist), adds to the oil to address either the oils shortcomings, (as with a conventional petroleum oil), or improve its performance, as with a high quality synthetic motor oil like AMSOIL. The vast majority of, "synthetic oils", available in today's market are
not formulated for safe extended drain intervals and have the
exact same recommended drain intervals from the companies that manufacture them as their conventional petroleum oil offerings do.
AMSOIL synthetic motor oils are formulated for safe extended drain intervals up to 25,000 miles and pioneered the synthetic oil industry for cars and trucks with the worlds first 100% synthetic API qualified motor oil way back in 1972, over 40 years ago.
Below is a link to an excellent article on synthetic motor oils and it will answer many your questions in-depth.
Synthetic Oil: Rx For Long Engine Life -
http://getahelmet.com/jeeps/tech/syntheticoil/
Below is a short video that covers the basics of synthetic oils and is very informative.
If you have any questions at all, feel free to ask. I'm an independent AMSOIL synthetic lubricants Dealer of close to 30 years experience and I can help you out.
