Re: oil changes

["Rich Wagner" <drsavage@domain.elided>]

Hi Joel, glad to see you're still around.  You wrote:

>Are you saying with synthetic oils you can go 12,000 miles between
changes? 

It depends on the manufacturer.  Amsoil can actually go well over 25,000
miles between changes.  Using their remote filter (which is a fairly large
unit), you can simply change the filter element at 25,000, and top off the
oil.  Really.  That's what they recommend.  You never actually change the
oil with that setup.  You slowly replace it instead.  I'm actually using
the Amsoil spin-on filters.  They cost about $10 apiece, making them more
expensive than most.  According to Amsoil, using their spin-on filters, you
can go to 25,000 and then do a full oil and filter change.  When I first
started using Amsoil in this car (an '89 Mitsubishi Mirage), I had access
to tribology equipment.  At 12,000 miles, I saw no excess metal, precious
little moisture, and the pH was still near neutral.  That indicates that
you can go more than 12,000, but I figured 12,000 was good enough for me. 
At 160,000 miles, the car is still running well, still getting around 40
MPG, and still has full compression.  It does use some oil, no more than
one quart every 1000 miles, depending on the driving conditions.  That's
coming in through the valve guide seals.


>Are the filters still filtering after that many miles?  

These Amsoil filters appear to be.  That's about all I can say.  I don't
know how other brands would work at that mileage.


>I have been changing my Mobile 1 every 5, 000 miles.  How does one decide
when to change it?

Except in the case of the synthetics, I have always followed the
recommendations of the car manufacturer.  I have yet to see a real, solid,
backed-by-data argument for changing the oil and filter at 3,000 miles.  I
feel that's excessively conservative and wasteful.  I don't know of a
single manufacturer that recommends changing it that frequently.  (Except
perhaps for a turbocharged model.)  Today, most manufacturers are
recommending 7,500 mile change intervals.  Without some form of tribology,
about the best you can do is watch the oil that you're draining.  In the
case of mineral oils, if it runs like water, you need to change it more
frequently.  I'm betting that the Mobil 1 comes out the same way it went
in, so that rule doesn't help you much.  Unless you're willing to accept
the possible responsibility of damage, I'd just follow the manufacturer's
recommendations for your car.  With synthetic, that will be very
conservative.


Rich Wagner
Montrose, CO
'82 GTV6 Balocco

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