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Originally Posted by deliriousga
Ours is changed between 10K and 15K miles. My wife tells me when it hits 10K and I change it when I get the chance, usually within a month or two, but we put 2K miles/month on the Boxster so it's never past 15K. With any car you should follow the manual, not what the guy who gets the bucks from the extra oil changes wants....
Hi, I agree with you to a point. You should follow the Manual, but you need to understand what the Manual is saying. The Oil Change Interval spec'd in the Manual assumes Ideal Driving conditions, which almost no car experiences. Ideal Driving conditions assume that; a.) Each time you drive the Car, you are driving 10 or more miles, b.) that you do not encounter Stop & Go situations, or periods of idle, c.) that your Fuel is Ideal - with the proper Octane Booster (some can contaminate the Oil sooner than others), d.) That your Plugs are ideal - READ: relatively New, e.) that your Air Filter is ideal READ: relatively NEW finally, f.) that you do not encounter any dusty conditions while driving. And it assumes all these conditions for the entire Service Life of the Oil.
Most Manuals also include a Caveat that the Service Interval should be shortened if Severe driving conditions are met. There is great ambiguity about the Ideal and Severe conditions mentioned.
But, every Dealer or Mechanic (who had any knowledge of cars at all) I have ever spoken to has said that Ideal driving conditions are really never encountered, and therefore the Change Interval s/b shortened. In my experience, using MB1, 10K mi. is about right for any N/A car. A Car w/ Forced Induction should place the Change Interval closer to 7,500 mi.
...As an aside, Consumer reports did a test a few of years ago to see if the every 3K oil change helped protect engines better. They took two each of several different automobiles with different size engines. One of each model had the oil changed every 3K miles and the other one had it changed according to the manual specifications. After 100K miles, they disassembled the engines and inspected them thoroughly. The verdict was no difference in wear, even microscopic, at all between the every 3K oil change engines and the manual spec change engines...
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Again, I have some conflicting reports, scientifically conducted, which state that there is an issue in changing the Oil religiously at the 3k mi. Interval.
In this Study, Oil samples were diagnosed in a respected Laboratory and checked for, among other things, the metal content of the Oil at different, specific, mileages, rather than disassemble and 'mic' the engine components as in the CR test.
This Study discovered a couple of surprising results. The biggest was that frequent Oil Changes actually
increase wear to the engine as noted by the increase in metal content of the Oil in the 1st 3k mi. after new Oil was installed. This is counter-intuitive, but this was experienced consistently with the new Oil. The reason is most likely that when Fresh, the Oil isn't actually operating at it's peak due to a full mix of Anti-Oxidants and Detergents. With age, these wane and the Oil actually does a better job of lubricating and flowing. I'd be happy to post a link to the Study if anyone is interested.
Happy Motoring!...Jim'99