RE: Oil Change Intervals

[zm@mhcnet.att.com (Zafer Mehmood [209])]

> 
> Nope.  
> 
> My average change interval is/was 7K miles.  I only changed the filter when I
> changed the oil.  I know it's better to change more frequently, but at 1K miles
> a week, it's just too much to do.  My thinking was that since Mobil-1 costs
> twice as much, I'd leave it in twice as long. If I had the time, I'd change the
> oil more often.  I really can't say that I caused any damage from my scheme,
> but I do think changing the oil more often is goodness.
> 
> ...bill
> 
> >Bill...
> >
> >I assume you change the oil filter every 3k/3mo?  I was told that you could
> >get 10K on synthetic if you changed the filter and added oil every 3-3.5mo.
> >So, would you say it would be good practice to dump all the oil on every
> >other filter change if the interval is 3-3.5 mos?
> >
> >Chris
> 

I think frequent filter changes are recommended if the synthetic oil
is not changed for extended periods like 15K or 20K miles. Yes, its hard to
believe, but there are people who use these intervals with synthetic oil.
Most car manufacturers specify oil and filter changes at 7.5K miles, so
the oil filter should maintain its filtering properties at least that long.
The main reason why frequent oil changes are recommended is to get rid of
contaminants (moisture, sludge, etc) that tend to build up with stop-and-go
city driving. Fossil oils tend to breakdown as well, especially so in hotter
running engines with turbos. Synthetics resist viscosity breakdown and sludge
buildup. And if one does a lot of highway driving and accumulates miles
quickly, as in Bill's case, oil/filter change intervals of 7 to 10K should
be fine with a synthetic.

Audi recommends oil/filter changes every 5K miles for my '87 5000 TQ.
I use Mobil 1 too and change it at 5K miles since I do quite a bit of
mixed city/highway driving. So far, the car has 127K miles with no oil
consumption between oil changes, and the engine compression is still within
factory specs for a new engine.

I see two reasons for using synthetic oil:

1. In turbocharged engines to prevent oil from coking in the turbo from
   extreme temperatures.
2. In cases where one puts *lots* of highway miles in a non-turbo car,
   where oil changes every 3K miles are way too frequent and the use of
   synthetic oil allows changes more infrequently.

In my opinion, a non-turbo car with average usage will benefit more from
frequent 3-4K mile oil/filter changes with a good quality fossil oil than
from synthetic. I would strongly recommend synthetic oil for turbo cars though.

BTW, I practice what I preach :-) I have 2 turbocharged cars and 2 non-turbo
cars. The turbos get Mobil 1, the non-turbos get fossil oil. Even the 5.6 litre,
238 hp V8 in my Mercedes 560 SEL gets regular old Castrol GTX every 3.75K
miles.

My 2 cents...

Zafer

-----------------------------------------------------------------
Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ