[Banzai]

When switching to synthetic oil, doubling oil change intervals applied to car engines, and only with premium synthetic products, and only in advertising hype of the early days of synth when dino recommendations went from 5K to 3K. Then, the early synth was supposed to be good for 6K+, but at the time it was almost 3-5X the price of a quart of typical mid grade dino oil. Even today, it's generally still at leat 2-3X the price of dino, making the advantages of synth out of financial reach or reason for the average user.

This is part of what I posted in another thread on oil viscosity choice:

Lets take a typical 10w30 oil. Multi grade oil has a tremendous amount of additives and chemical manipulation that causes the base oil, in our example a 10 weight, to swell when heated. It has to be thin enough to NOT cause as much parasitic drag on the engine under high load start up, but has to be thick enough to provide lubrication and protection to critical engine parts. As the oil gets to operating temp, the molecules swell and thicken, until it will test as viscous as straight 30 weight oil, providing maximum engine protection. It's those chemical modifiers/molecules that cause the oil to 'swell' that break down and burn off first, followed at a slower rate by the base oil.

There is TONS of research and independant info that shows that dino oils typically loose half their viscosity in car engines about 1800-2000 miles. It's a testiment to the modern materials that the engines continue to run well under those conditions. Usually, by 3000 miles, testing shows that dino oils are at about 1/3 their 'new' rated viscosity, as well as hyper contaminated with the products of combustion and break down.

Thus, a typical mid grade (that most of us use) Havoline/Penzoil/Quaker State/Mobil 1/insert brand name here 10w30 oil, after 2K miles will test something like a 5w15, and by 3K is so contaminated and broken down it tests in the neighborhood of a 3w10. That's why an engine burns oil the more it's used, and why it's normal to have a lower volume of used oil than when you put it in new!

Research in the late 80's and early 90's discovered this, which is PART of why pre mid-90s engines had a life expectancy of only 100K miles and why oil change intervals WERE 5000 miles but are now 3000 miles for they typical auto.

Better oveall oil additive packages to prevent break down, increase heat tolerance, materials science, and advances in machine tools now let us make a better engine than ever before, but recommended oil change intervals haven't gone back up (some manufacturers recommend higher intervals in their owners manuals, but they also specify HIGHER GRADE oils with that increase!!!). Of course, there are some exceptions!

One would be the motorcycle, especially one that shared engine oil with it's gearbox and clutch.

Still wanna stick to that oil change interval as recommended?

And the final answer for best protection, as recommended by so many independant researchers, is chaning the oil NOT LATER THAN every 3K miles (for dino). They're a bit more disjointed on their recommendations on synth, but I've never seen it recommended to go as long as the synth manufacturers recommend, and never more than 5K, and NEVER the hype of 'double the oil change interval' that was so prevalent in early sales literature for synth oils.

Bottom line, though, is that changing the oil more often, but within reason, is the best protection.