I have had oil analysis done on Mobil 1 drained out of our Olds when the
monitor said 20% left, and the oil analysis people indicated that the oil
still had plenty of useful life in it.
IMO, GM's oil life monitor system is pretty sophisticated as it takes into
account start up cycles, engine rpms, engine loading, etc. All of these are
real factors which effect oil's useful life. GM's system assumes standard
motor oil, so by using synthetic you are buying yourself significant extra
I now run Mobil-1 in our GM vehicles until the oil life monitor gets down to
around 15% useful life remaining and then I go ahead and change it. This
interval can end up being as short as around 4500 miles if the use is mostly
around town driving or almost 10,000 miles if long cross country highway
trips are involved. This procedure is still very much overkill and I could
be running the oil longer on synthetic ... but I have not been able to bring
myself to do so.
If you really want to be sure, spend $25 on a professional oil analysis of
your situation. www.blackstone-labs.com is the place I have used.
I think you will find individual differences from one GM to another.
On mine, for each start-up, if I go less than three miles, then it counts that
up toward a 3000-mile oil change. If I go more than three miles, then it counts
that up toward a 7500-mile oil change. Then the oil life is calculated from
that and displayed on the dash in terms of percentage remaining. Since I nearly
always go many more miles than three, mine nearly always counts toward 7500
miles. However, since my driving is a mixture of easy and hard, I always have
the oil change at 5000 miles.
The GM link referenced above says nothing about differences from division to
division. I can imagine that the tuning of the system variables could well
be different for different powertrains and/or vehicle types as each
situation is different in it's oil wear out characteristics, but I doubt
that GM's oil life monitor would be engineered differently by brand
designator. I would bet big money that a Chevy Venture minivan would have
the same oil life monitor system as does it's sister vehicle the Pontiac
Montana. It has been many decades since the individual divisions of GM
even had their own engineering staffs (though Cadillac is sort of getting
one back now).
GM is doing a very good thing by giving a much more rational indication of
when to change a vehicle's oil than can ever be achieved with simple minded
Sorry, I disagree.....GM isn't trying to do anything good other
then attempt to lull buyers into believing that their vehicles are
"low maintenance" vehicles. Which will work fine for the lease
type of buyer who basically blows off the car after 3 years.
Any car will make it to 3 years and 60K klms with little or
no maintenance. It's after that that the real problems with
lack of maintenance start to show up. But does GM or
the customer that unloaded the car after the lease was up
care? No, why should they? They are no longer financially
responsible for the car.
The more "rational" approach is to use a distance/time
schedule. I see the results of "extended" oil change
intervals every day.
The Mobil1 is good... but change your oil and filter every 3K miles
(or whatever km that equates to). Forget the monitor. Your engine
will thank you for it.
On Tue, 20 Jan 2004 11:34:31 -0500, "Twitch"
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Yup synthetics last a good long while but the filter is questionable.
Remember when Corvettes were recommended to have their first oil change
at 40k miles? Dunno bout any of you but I wont be waiting that long to
change the oil in a $50,000 car.
foolspicedham_melbo email@example.com says...
I think it was on a memo they put out. They were having oil consuption
problems with them. I think synthetic was keeping the piston rings from
breaking in so if you kept it in longer the oil would wear out enough to
allow the rings to start seating themselves. If you look it up I think
the oil change interval for C5 Vettes is 10k miles. So long as your
using the recommended synthetic oil that is. Personally I would run
conventional for the first 500 and 2500 miles for break in then switch
What do you base your suggestion on? Do you have any data? I doubt it. It
sounds like you are simply repeating a decades old rule of thumb. In the
real world oil life varies dramatically as a function of engine design,
driving conditions, etc.
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