some things to consider...
most of you already know and will agree that oil changes are probably the most important maintenance procedure there is for a car.
that having been said, i see this issue of "breaking-in" oil a couple of ways. but first, let's look at the function of the oil in order to provide everyone with some background info that not all people may be aware of.
crankcase oil serves several purposes. it lubricates, cleans and cools the engine. it has been said that oil in an engine is the equivalent to blood in the human body. as you all know, blood's pretty important.
on the lubricating end, oil provides a protective layer between the moving parts to prevent/reduce wear. with the extremely tight tolerances produced by today's machining methods, this becomes more critical than in engines of a few decades ago because the amount of space between parts has been reduced from say .012" to in the neightbourhood of .003".
oil also operates as a medium in which particles in the engine can be suspended and kept away from the critical moving surfaces. this is why it is important to change the oil hot. by running the engine to operating temp, not only does it make the oil flow easier, but it allows all the dirt and sediment to be suspended within the oil as opposed to being stuck at the bottom of the oil pan where it doesn't get removed from the engine and just contaminates the new oil.
remember when new cars needed to be "broken in"? this meant initially driving at slower speeds and gradually working your way up over a period of 5,000-10,000 miles. if you'll all recall, the first oil change was usually around 1,000-1,500 miles. that's how it was with my jeep.
because the degree of precision was less then than it is now, the components needed to wear against each other in order to seat properly. this is why oil changes during the break in period was so crucial. the particles that had worn off needed to be removed from the engine.
now that is not as neccessary. as can be witnessed by manufacturers claims that one could drive up to 10,000, or in some cases 20,000 miles before needing to change the oil.
the key factor with oil is its viscosity. that's why there are different grades available for different times of year. summer grade is usually 20-50 and winter grade is 10-30, and we all know that 20-50 is noticably thicker.
thermal breakdown of oil begins immediately. and thermal breakdown is not a good thing. it reduces the oil's ability to lubricate the engine and also reduces the oil's ability to cool the engine because the thinner oil will heat up faster. this is just basic thermodynamics.
the other downfall to waiting too long is the buildup of particles being suspended within the oil. at some point, the ratio of particles to the volume of oil reaches a level where it becomes destructive and could actually result in faster wear of critical components.
on the basis of the function of the oil in relation to the engine, it's better to change the oil more frequently than less. however, you have to balance the need of changing the oil with the cost. it's pointless to change the oil every 1,500 or 2,000 miles because the oil hasn't broken down to the point of being useless and you wind up just wasting your time and money.
by the same token, pushing your oil beyond 5,000 miles is not good either because of the level of breakdown that has occurred.
every 3,000 miles is generally accepted as the best interval at which to change the oil and filter.
now, with regards to breaking in oil. probably the only argument in favor of this is that if you choose a grade that is too thick, you can do damage to your engine as well. thicker oil takes longer to heat up and moves more slowly, so, in a cold start situation, the oil takes longer to circulate through the entire engine on startup leaving some parts unlubricated for a longer period of time. it's also more strain on the oil pump, and other components to deal with the thicker and heavier oil. which is why you should always follow the manufacturer's recommendation for the grade of oil that you use.
as far as synthetics go, they are advantageous because they don't break down as quickly as conventional oils so you could go longer with a synth before it breaksdown completely. BUT, remember what i said about suspending particles and the number of particles per volume of oil? that still applies. although synthetics reduce wear and hence the number of particles over a given period of time than the conventional oils, clean oil is every biut as important as oil that has maintained its viscosity.
i personally don't used synths because i change my oil every 3,000 miles and i am religious about this. and considering that synths cost almost 2x as much as conventionals i'd rather change twice as often and CLEAN the engine twice as often. than spend twice as much and letting the crud sit in my engine twice as long.
a couple of other notes regarding oil:
the molecule of a synth is considerably smaller than that of dino. this is why quite often when switching to synth, people discover oil leaks that didn't exist before.
because synth doesn't break down as fast, this is why they can make synth more of a multigrade than dino and still retain the effectiveness of the oil.
too much oil in the crankcase results in cavitation in the pan by the crankshaft. this puts too much air into the oil in the form of bubbles and results in less oil and more air being pumped through the oil journals to the bearings, etc.
and that concludes today's lesson :-)
'94 W124.036 249/040 leder; 8.25x17 EvoIIs
'93 W124.036 199/040 leder; 8.25x17 EvoIIs, up in flames...LITERALLY!
'93 W124.036 481/040 leder; euro delivery; 8.25x17 EvoIIs
'88 R107.048 441/409 leder; Euro lights
'87 W201.034 199/040 leder; Euro lights; EvoII brakes; 8x16 EvoIs - soon: 500E rear brakes
'70 R113.044 050/526; factory alloys; Euro lights