Miata Mailing List: February 2000, Message #113

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Although a lot of car and oil mfgrs now recommend high mileage oil changes
they have yet to convince me.  There are only two reasons to cycle your oil
at all, 1) to ensure proper lubrication and 2) to rid the engine of
contaminants.  Most modern dino oils provide lubrication far in excess of
what the mfgr recommends for change intervals so changing for lubrication is
pretty much a moot point *but* maintaining oil free of suspended
contaminants for long periods is a problem oil manufacturers haven't solved
yet. The longer an engine operates, the more contaminants are collected.
Eventually, over time, constant high levels of acids in the oil will cause
damage and filters don't remove them.  I change at 3K mile intervals for
this reason, by doing so I know my oil contains the minimum of these acids.
IMO you gain a lot by changing whatever oil you use often, but with a street
driven car I don't think you gain much by switching from dino to synthetic.
You still have the contaminants to deal with and any gain from 'reduced
friction' etc. is more then offset by the heavy premium paid for the stuff.
We're talking street driven stuff here, not some toted to the track racer
with a full on competition engine.  The Miata engine was made to operate
just fine on dino oil so unless your spinning a highly stressed engine way
beyond where you should be and pumping out gobs of aftermarket hp, IMHO
synthetic oils are a waste of money.  Of course if you gotta have the
absolute best needed or not, it's hard to argue with Synthetics, but then
everything's a trade off.  Whatever floats your boat.  My .02 worth.

Hank & Belle
'99 Silver
RAGS 57
Murphy, NC