My understanding is that this limitation does apply to synthetics.  However, since I am not a
CE, my information is second hand.  I would check the engine oil bible web site, if it is still
up.

My understanding is ...

The benefits of synthetic are:
  - Improved lubrication
  - Ability to flow at lower temperatures
  - More stable base stock
  - Leaves fewer deposits in engine

The detriments of synthetics are:
  - Cost
  - You should not use in an engine with more than 24,000 mi that had previously used
    conventional oils, unless the engine is flushed first

Synthetics are not high mileage oils, simply because:
  - Modifiers break down
  - Contamination builds up (dirt, moisture, etc.) just like in conventional oils

I have been using synthetic lubrication (engine oil, transmission oil, grease) in all of my
vehicles for the last 12 years, and I still follow conventional maintenance schedules, including
changing the oil/filter every 3 mo/3,000 mi.

--- On Thu, 9 Oct 1997 12:30:52 PDT  David Bayer <bayer@SYBASE.COM> wrote:

>>| With a 5w50 oil, the base stock is 5W with modifiers to make it act like its up to 50W
>>| at higher temperatures.
>>|
>>| The problem is, these modifiers break down over time, even in as little as 2,500 mi.
>>| Once this happens, you basically have base stock oil, in this case 5w, which is too
>>| thin for pre-1990 engines.
>
>        Is this true of a synthentic as well? I know dino oil burns itself
>into varnishes over time, but isn't the "benefit of a synethic that people
>mix a bunch of polymeres together that are much more stable in the thermal
>ranges seen inside an engine? Or even blend the polymers to change viscocity
>to correlate with the needs at specific temperatures? Or is this just a
>myth of synethics?
>
>dave

-----------------End of Original Message-----------------

______________________________________________

  "Michael Stocker" <mdstockr@neo.lrun.com>
           10/9/97 4:46:29 PM EDT
______________________________________________