Hi Klaus

I won't yell...

I'm an engineer, and I work on a wide variety of hydraulic machinery. For various reasons most of these systems use petroleum derived fluids. And it gets changed regularly, even though it still tests perfectly good. I have always changed the oil in most of my cars with that same sort of mind set.

But your response raised an interesting question. As we both know, the old wisdom of changing oil, as opposed to changing just the filter and adding oil as required, was based primarily on the fact that older styles of petroleum lubricants did indeed "break down" during the course of their service lives, losing their lubricating characteristics and leaving behind all sorts of nasty deposits. But the nature of the most modern synthetics is such that they undergo very little molecular change during the course of normal use.

It also now seems to be conventional wisdom that the primary reason to change oil is to remove the micro-particulate byproducts of combustion. That would seem to mean that if the filtration system is adequate to remove the contaminants, as well as any metals or foreign materials, changing the filter and adding oil to compensate for a vehicle's normal consumption should indeed be perfectly acceptable.

Have you (or anyone else) ever come across anything definitive that explains why synthetic oil has to be changed at all, if sufficient filtration is present? Or is it just intuitively that the old stuff should be dumped at some point, even if only once a year.

By the way, I still use dino oil, and change it every 3500 or so in my turbo.

Best regards

Marty
'96 855T