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When To Change The Oil


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Jan 10, 2002
Edmonds, WA
Well, it's coming up soon, in another two weeks or so my Avalanche should hit the big 3,000 and be ready for oil change number one, or maybe not.

I've read in other publications that the change oil monitor in GM products works pretty good, and general advises an oil change between 3,500 and 5,500 miles - but can come on as early as 2,000 or as old as 10,000 depending on driving conditions.

So - if I change the oil at 3,000 miles I basically render this feature useless. There is no way to reset it back to zero when you change the oil (which would be ideal because under abusive conditions you could get an early warning) and it will, in all likelyhood come on between oil change one and two.

The cynic in me says this feature would be good, but not TO good. General Motors does have a vested interest in making sure my Avalanche doesn't last forever.

So what are folks doing here. Are they changing at 3,000 miles or are they waiting for the change the oil light to come on.

BTW - I'm going with Mobil One from this day forward...
I am following the General's suggested method for now in regards to oil changes. The Change Oil monitor came on the first time at about 6,500 miles and she has about 11,500 now without the 2nd light so far. Lots of highway with sustained running at 90MPH...the monitor must not consider that under the extreme operating conditions calculations? ??? ??? ???
It's a nice gimme from Chevy, but I change my oil Religiously every 3000 miles. I view the sensor as idiot proofing the truck for those people who can't remember such maintenance tasks.
I try to change mine every 3000 miles as I drive aroun 2000 a month or more.

You can reset the oil change light at every fill up...It is in the manual...If I remember correctly you turn the key to on then pump the gas pedal 5 times fast and the light will blink oil change reset or something like that.

PS I am going for change numer 3 in a few days.
Took my AV in for first LOF this morning at 3015 miles. I am from the old school and will just do it (have oil changed that is) every 3000 miles.
When do you all plan on changing the tranny and differentials?????

Also what about the DEXCOOL? Will it really last? IT rarely gets below 32 here but it sure can get hot!

Maybe we should have some sort of owner reccomended maintenance schedule thingy ot whatchamacallit? ;D
You have the recommended schedule. Look in maintenance section of your manual. They list what needs to be done, and when. :D
I know but I wonder if people recommend different for a better longer lasting avy ;D
the sensor is actually very usefull. if you ever decided to change your oil, which i've done twice already, and the light/reminder has not come on, all you have to do is complete your oil change, turn the key to the run stage (not start), and pump the gas pedal 3 times. then, when you start the truck, the oil chane light will flash as well as chime.

and walla, it's reset...
Thanks j166! Something my dealer told me wasn't possible :mad:

That makes a lot of sense to me - now it does serve a useful purpose. I can change my oil ever 3K to 4K miles, reset it, and then if I do any heavy duty use like off road, or pulling trailers and I need it sooner, I'll be warned. That IS a good feature!
I did my first two oil changes at 3K miles. I am at 6500 miles now and from the last oil change I am going to let the light tell me when to change the oil. If it's at 2K or 8K miles. I will try it for a while see how it acts with my driving.

As far as the dexcool I will wait for about 80-90K miles before I change it. I did this with my old 96 K1500 Z71 and did not have any problems. I even waited on the plugs, wires, and dist. cap till about 80K miles before putting new ones on. When I traded it in I had about 125K miles and did not have any problems with my engine.
What does the change oil light work off of for a sensor????

Is it mileage based or dirt in oil based or ???? ???
According to the owners manual it monitors engine hours, load (on the engine), temperature of operation (outside) and driving style (highway, excelleration, etc.). ?I guess it uses some formula of all of the above to reach a conclusion on when the oil SHOULD be worn out.

As I've mentioned earlier, what I've read says it works very well. ?I know it has been around on GM products for at least five years, and maybe even ten...
I change oil in the 5,000 mile range (mostly highway miles) but I ket the OLM go just for grins. It's closing fast on 6,000 miles since I last reset it.

Dexcool can go the distance. I changed our '96 Bonneville at 150,000 and there was no evidence of sludge or anything else. At 186,000 now, the 3800 Series II is going strong and the Dexcool still looks clean. Originally, the recommended change interval was 100,000.

I liked the Dexcool so well that I converted my '92 Jimmy to it and changed it at 100,000 mile interval.
You won't have to worry about changing any distributor cap or rotor. Kind of nice having a coil for every cylinder.
I don't think replacing the wires should be too much of a problem since you don't have to worry about the firing order. Couldn't be any easier. The oil sensor doesn't work off how much dust is in the oil. The book says to change the oil more often if you drive in dusty conditions. In my 99 Silverado I always waited for the oil light to come on. It never went past 5,000 miles. All my miles are usually highway miles. The oil was never even close to being black.
I did the first oil change believe it or not at 1500 k....I'm one of those firm believers in getting rid of any metal shavings from a brand new engine asap.

After that full synthetic, every 3000k....
Im going to be changing the oil in mine every 3000 miles only because my dealer (Main Street Chevy in Cartersville, GA, excellent buying experience BTW) offers a 250,000 mile warranty on the engine if you let them change the oil every 3000 (+/- 500) miles. I can live with that especially since they only charge 16.95 for a standard oil change. I am however going to switch to Mobil-1 after the third oil change. I hear you arent supposed to switch any earlier than around 9,000 miles. Any thoughts on this?
I am looking at Royal Purple - my chief machinist is in love with the stuff - even uses it in his lawn mower - big lawn. He won't let me change before 12000 - can't argue with the guy.
I too, have heard rave reviews of Royal Purple (have also seen it used on HP TV, PHR, etc...), although it is probably very similar to Mobil 1 in its effectivness.

I had been wondering how long to wait before going that route, thanks for the info. guys, guess I'll wait till 10-12K now...
The consensous answer is to let the engine burn in on "dino" - get everything seated and used to each other I guess. Corvettes come from the factory with Mobile 1 supposedly, but ar also supposely run in.

Any other sources of wisdom lurking here?
Briefly, engine oil degrades in a
predictable fashion, according to several
measurable engine operating conditions.
The engine control module counts
combustion events (measured in rpm)
and reads coolant temperature. From
these numbers, the computer is able to
track oil deterioration and notifies the
driver when a change is needed.

The best value from the cost of an oil
change is obtained by maximizing the
mileage between changes, so long as
there is no adverse effect to the engine.
With the GM oil life system, the average
person can expect oil change intervals of
4000-7000 miles for mixed driving, and
7000 to 10000 miles for highway driving,
while the Chevrolet Corvette and the
2002 Envoy, Bravada and TrailBlazer can
achieve 15000 miles under ideal

Since the GM oil life system first
appeared on some 1988 Oldsmobiles,
over 10 million have been built,
presently at the rate of over 3 million a
year. By model year 2003,
GM expects to install oil life
systems on essentially all
cars and light duty trucks.
This past May(2000), the GM
oil life system development
team was honored by
receiving the first ever
Environmental Excellence
in Transportation award
from the Society of
Automotive Engineers. This
award recognizes that the
extended range offered by
the oil life system can save
huge amounts of new oil,
and can keep thousands of
gallons of used oil out of
the environment.
There?s a lot of information on vehicle
maintenance shared on consumer-oriented
websites ? some correct, come
erroneous, and some simply outdated.
For instance, conventional wisdom calls
for oil changes every 3000 miles. Not
surprisingily, this conservative figure is
also supported by those who derive
income from selling oil changes. Many
of your customers have become
convinced that any longer oil change
interval is somehow harmful to their

At the retail level, you can do your
part by promoting proper use of the GM
oil life system. Become familiar with its
function, and be prepared to help
customers understand that observing
the montor?s recommendation is the
easiest way to take the guesswork out
of oil change intervals. It also ensures
that they are giving their vehicle the
proper care it deserves, at the minimum
expense. :) ;D :cool:

? Thanks to David Staley
and Chuck Burns
tommy said:

Hey Tommy. If you put synthetics or additives in too early, things may not seal properly and long term your engine can start to burn oil. That's why in many cases they recommend waiting at least 3,000 miles. Some purists will tell you to wait to 9,000 miles. It can't be all bad, some BMW, Range Rover, and Porsche models, as well as the Corvette come with Mobil 1 in them right out of the box.
Oil Life Monitor --
How Does It Know?

How long will oil last in an engine? What
reduces the oil?s effectiveness? When should
it be changed?

Lubrication engineers perform a number
of tests to answer these kinds of questions.
Vehicles are operated under prescribed conditions,
and periodically a sample of the oil is
taken into the laboratory for analysis. When
the condition of the oil is no longer satisfactory,
the mileage is noted.

From controlled testing like this, engineers
in the past have determined two sets
of mileage numbers, one number for normal
driving and the other for severe conditions.
Severe conditions can mean that the vehicle
is driven hot (for example, pulling a trailer up
a mountain) or is driven such that the oil
never warms completely (for example, trips
less than 5 or 10 miles in a winter climate). It
is then up to the owner to decide whether
their own driving is normal or severe and to
change the oil accordingly.

Now, science and technology have found
a way of taking the guesswork out of the picture.
GM is installing an oil life monitor in an
increasing number of new vehicles. Using a
simple indicator lamp or readout on the
instrument panel, this system notifies the driver
when to change the oil.

The February and March 2000 issues of
TechLinkexplain how to reset these monitors.
Here?s information on how an oil life
monitor works.


Straight oil is not an ideal lubricant in an
engine. A package of additives is needed to
give the oil properties it does not naturally
have or to enhance its natural properties.
Some of the tasks accomplished by additives:
- viscosity modifiers, to keep the oil the
proper thickness over a wide range of
operating temperatures
- anti-oxidant, to keep the oil from
- corrosion inhibitors, to protect
engine components
- anti-wear
- anti-foam
- detergents, to suspend solid particles.

What Makes Oil "Wear Out?"

If you were to start out with a crankcase
full of fresh, clean oil, and drove the vehicle
for a period of time, eventually the oil would
have to be changed. During this time, what
can change fresh oil into "worn out" oil?
First, dilution. When gasoline is burned in
the combustion chamber, the by-products
include a lot of water. Some of this water can
find its way into the crankcase through piston
ring blow-by. If the engine is cold, and if combustion
is not perfectly complete, a small
amount of acid is formed. It, too, can blow-by
into the oil. You don?t need to be a top-notch
scientist to realize that water and acid aren?t
good things to pump through the lubrication
system of the engine. If an engine is run long
enough for the engine oil to warm, the water
and acids will evaporate and not accumulate.
But, during very short trips in cold weather,
water and acids can enter the engine oil and
cause the oil to "wear out."

Second, the degradation of the oil and its
additives. We mentioned earlier that a number
of additives are put into oil to improve its
performance. If these additives are degraded
or decomposed, the oil is no longer capable
of doing all of its jobs properly. Oil with
degraded additives can become thick and
dark. Additives become degraded by exposure
to extreme heat. There are two places a
lot of heat can reach the oil. One is near the
combustion chamber. Oil at the top piston
ring is exposed to very high temperature.
And some bearing surfaces can also put a lot
of heat into the oil at high operating temperatures.
So, degradation of additives from high
temperature operation is the second factor
that can cause oil to "wear out."

How Can Operating
Conditions be Used to Predict
Oil Life?
Using carefully controlled laboratory
tests, it?s possible for lubrication engineers to
measure how long it takes to dilute engine oil
during cold operation. And it?s possible to
measure how long it takes for high temperature
to degrade the additives.

We usually think of measuring time in
hours and minutes, but for an engine, the
amount of revolutions it has run is also a
good measure. So for the purposes of oil life,
time is measured in engine revolutions.
Engineers like to talk in terms of models.
A model is a way to describe something
mathematically. It?s possible to create an oil
life model that very carefully matches the
results of analyzing the oil in a laboratory.
The oil life monitor, then, is based on a
model. A computer chip in the Powertrain
Control Module is loaded with a certain number
of engine revolution counts. The count
for each engine/vehicle combination is determined
by testing. As the engine runs, each
revolution is subtracted from the remaining
count in the oil life monitor. When the count
reaches zero, the instrument panel light
comes on. But, here?s the clever part. When
the various input sensors detect that the
engine is running under either cold or hot
conditions, it subtracts extra counts (penalties)
for each engine revolution. So, the conditions
that cause the oil to "wear out" make
the counter run down faster.

When the oil is changed, it?s necessary to
reset the oil life monitor (see the February
and March 2000 issues of TechLink) and the
countdown begins again.

NOTE: Synthetic oil resists "wearing out"
better than mineral oil, so the oil life monitor
is set to account for this, but only on vehicles
that are specified for synthetic oil from the
factory -- the Corvette, for instance. Using
synthetic oil in other vehicles is certainly not
harmful, but the oil life monitor will continue
to count down as though the engine contained
mineral oil.
What about the recommended changes from the manual versus the moniter thingy?

IF engine problems crop up how can you prove you changed your oil per the moniter?