Ok .. now I have some questions about this .. and reading it back, its turned into a book ... sorry bout that but I'm looking for real feedback here ...
Most vehicles I've owned since 1982 (and probably before) had intervals in the owners manual saying oil changes should be done every 7500 miles with standard oil (not synthetic) under regular use. When it's driven mostly city stop and go traffic (like Taxi's), off highway high dust environments, high heat, etc. were considered heavy duty and most of those said between 4 and 5000 miles. It's my understanding that part of this need to change oils is because the oil breaks down, partly because of contaminants. Synthetic oils increase this interval because they don't break down like the standard oils but they need a better quality filter to be able to clean out particulates. Standard oils manufactured today have an increased longevity too - not as much as synthetic but still oil's much better made now than ever.
So, here's the questions I have: If the MFGR says to change oil every 7500 miles, isn't that based on their testing of longevity? Many new vehicles have 100,000 mile warranties - some lifetime. It would be in the manufacturer's best interest to lower these intervals if there's so much potential for damage, right? And when it comes to mfgrs recommending synthetic oils; and BMW, VW, SAAB, Land Rover, Jag - there are many, their recommended change interval is upwards of 10K to 12K and more miles. Again, if these long intervals are so bad, wouldn't it show up with reduced long term reliability and ultimately be bad for the manufacturer?
BTW: I did some searching, in the data I have the only US manufacturer recommending 10+ oil change intervals since 2001 is Chrysler (including Dodge and Jeep).
Really not wanting to be argumentative here and yes - changing oil more often than recommended usually doesn't hurt anything but when the MFGR says to change the oil every 12K miles and people change it every 3K miles ... it just seems to be extreme overkill.
Some of you more mechanical types here that recommend changing oil more frequently, do you do so because you've always done it that way or is it because you've got real stats saying changing oil at 5K or 10K miles - per manufacturers recommendations - is genuinely harmful to the engine?
And yes - I know the difference between standard oils where MFGR's usually recommend 7500 mile change intervals and synthetic oils where MFGR's recommend 10K+ change intervals. ... I'm talking specifically about when the manufacturer recommends one change interval and others recommend a much more frequent interval.
You got to consider that most do not keep there vehicles for very long,most trade in right after the bumper to bumper warranty expires.Those extended/lifetime warranty's in most cases are only for the original owner and can not be transfered.If you have ever tried to get a engine replaced using one of those extended/lifetime warranty's you know it can be a royal pain(not always though) if you can not prove you did your oil changes on time.
So this passes the problem to the next owner that is unaware and he's SOL since it no longer has a warranty and why you see so many complaining poeple on forums like these.Any engine regardless of who made it or where can take the abuse of neglect for 60,000-100,000 miles with no issues at all but say at 110,000 miles all hell breaks loose and your stuck buying a engine or taking a big hit and buying another vehicle.Just this week I changed the oil on a '05 Chrysler 300 with the 3.5 and it still had the factory installed oil filter on it(stamped right on the filter,dated also) with 74k on the ODO,that oil did not look good coming out.The record I've personally seen was a '02 Subaru with 124k on it with the original factory installed oil filter.
I see the end results of extended OCI's all the time at work and it's not cheap nor pretty.Some may never have a issue but others will have endless issues and why over 90% of all ASE Master Tech's still recommend 3k OCI's.Now it's not so they have more work as anyone in the trade will tell you a Master Tech is the last person any shop wants to change the oil since the shop will loose money paying there higher salary.
Just remember oil is cheap,engines are not.It's not a waste changing every 3k,your going to be dead before we run out of oil anyways and almost all used oil is recycled or burned as heating fuel anyways so no real enviromental impact from changing more often as the greenie's think it is.