: adding oil between oil changes

01-08-09, 04:21 PM
how much oil does the 4.6 northstar hold? its been 2500 miles since last oil change and i am in the "add range".. i knew i would need to be adding oil soon last i checked it was just at the line above add. is it normal at 2500 miles that my car would use that much oil.. i know its a quart every 750-1000 miles but i am not sure if i have used more than that. my oil life index is around 30. thanks!

01-08-09, 05:33 PM
Your (93 ???) Northstar is designed to hold 7.5 quarts of 10W-30 oil. The "Oil level" warning will come on at two quarts low. If your dipstick is at the "add" mark on the hashmark, then you should be at the 2-quart mark. Northstar oil consumption varies all over the map, so if you have used 2 quarts in 2500 miles, that's a quart each 1250, which is decent consumption for a Northstar. The 30% in 2500 miles is questionable. Do you do primarily short trip stop&go driving ? That's what kills engine oil. Maybe the oil life monitor was not reset. Reset it each time you change oil and filter.

01-08-09, 05:37 PM
Go to the top left of this page and click on Technical Archives. Read up on OIL CONSUMPTION.

01-08-09, 06:48 PM
Ok thanks guys.. only 2 quarts is good news. what could the oil life index indicate if it was correct and at 36%?

01-08-09, 06:58 PM
:rolleyes: IF 36% is "correct" it says that the car never warms up and idles 90% of its running time. OR that the engine oil has been severely overheated one or more times......very unlikely.

Your engine and the oil in it suffers more "wear" in a week of city driving than it does on a round trip from Maine to Florida.

01-08-09, 07:02 PM
I don't understand the question.

Disregard. After reading Subs answer, I think I understand what you where asking and he answered.

01-08-09, 07:12 PM
i do a lot of city driving. the most driving i do on the highway is 20 miles out, and back. other than that my trips are short and on roads with stop signs/traffic lights. i have never seen my engine temp. above 221 degrees, and that was when my heater core went and i was low on antifreeze.

01-08-09, 07:17 PM
my trips are short and on roads with stop signs/traffic lights.
That is why it decrements so fast, especially in the winter.

01-08-09, 07:34 PM
That is why it decrements so fast, especially in the winter.

good to know.. thanks!

01-08-09, 11:29 PM
Does teh oil consumption increase with colder temperature like at or below freezing?

01-08-09, 11:52 PM
The GM oil life system is based on revolutions and oil temp. If you overheat it it will degrage the oil. if it's too cold - never warms up, I think it calcs that as well. One time i got a change oil indication after only about 1000 miles after a change and found out that the primary engine cooling fan motor was burned out!! so it works!

01-09-09, 05:10 PM
It actually takes much much more into account. Things like outside temperature, RPM, engine temp, throttle position, just to name a few. I think I have the detailed explanation at home and can post it if interested, but that won't be till late tonight or tomorrow.

01-10-09, 01:15 AM
My car (http://www.cadillacforums.com/forums/album.php?albumid=240) is driven daily 60 miles round trip 90% highway or roads with 55MPH speed limit and few traffic lights. I can say almost the ideal trip for the car. I drive the car pretty hard but after 3000 miles my oil life indicator is consistently ~54% - thatís when I change the oil.

01-10-09, 04:29 PM
My car (http://www.cadillacforums.com/forums/album.php?albumid=240) is driven daily 60 miles round trip 90% highway or roads with 55MPH speed limit and few traffic lights. I can say almost the ideal trip for the car. I drive the car pretty hard but after 3000 miles my oil life indicator is consistently ~54% - thatís when I change the oil.
That's about right. yours is capped at 7500 miles and if you followed the OLM, that's right about where you'd be when it told you it was time.

05-05-09, 06:43 PM
My car (http://www.cadillacforums.com/forums/album.php?albumid=240) is driven daily 60 miles round trip 90% highway or roads with 55MPH speed limit and few traffic lights. I can say almost the ideal trip for the car. I drive the car pretty hard but after 3000 miles my oil life indicator is consistently ~54% - thatís when I change the oil.

so change at 54% or when the car says too?

05-05-09, 07:20 PM
Your choice.

05-05-09, 07:30 PM
it wont cause harm to engine if i go by the oil life meter?

05-05-09, 07:35 PM
Of coarse not. Imagine the law suits if it did. In fact they won awards for it.

05-05-09, 08:04 PM
it wont cause harm to engine if i go by the oil life meter?

Let's agree to call the GM application the Oil Life Monitor.

Which is exactly what the patented GM system does; it monitors countless engine operating parameters to provide an accurate forecast of when the oil should be changed. With a considerable margin of safety.

Not to be confused with maintaining the crankcase oil level. Two different issues.

Mindless three thousand mile oil changes are for collector cars and 4th of July parade cars. For (most) daily drivers, 3,000 miles is far too soon and a waste of crude product. For the remainder of daily drivers (in the upper mid-west and Alaska), 3,000 miles could easily be too far.

It's your engine -- and your money. But my '98 model has (so far) accumulated 184,xxx miles on oil change intervals dictated by the Oil Life Monitor (oil change average = 6,600 miles).

05-05-09, 08:12 PM
yeah i thought that 3k is too soon and read stuff about it online just trying to keep my eldo in top shape. i am at 50% and i added 1 quart yesterday

05-05-09, 08:20 PM
ok i found this its a good read it answerd all my questions

GM Oil Life Monitor System
Frequently Asked Questions
How does the system work?
The GM Oil Life Monitor System is not a mileage counter. It is actually a computer
based software algorithm that determines when to change oil based on engine operating
conditions. There is no actual oil condition sensor. Rather, the computer continuously
monitors engine-operating conditions to determine when to change oil. Over the years,
millions of test miles have been accumulated to calibrate the system for a variety of
vehicles. The system was first introduced in 1988 and is now on more than 10 million
GM vehicles.
How do I operate the system?
The GM Oil Life Monitor System is very easy to use. First, refer to the vehicle owner’s
manual for a description of the specific ‘change oil’ message and the instructions for
resetting the system. When the vehicle has been driven the appropriate miles, the ‘change
oil’ message will be illuminated on the instrument panel or driver information center
when the vehicle is first started. An oil change should be done within two fuel tank fillups
from when the message was first displayed. Immediately after the oil has been
changed, the system must be reset. After resetting, the ‘change oil’ display will no longer
be displayed after engine start up.
I change my oil every 3000 miles, so of what use is this system?
You can continue to change your oil every 3000 miles if you so choose, but remember to
reset the system after changing the oil or you will get a false “change oil” message.
However the GM Oil Life Monitor System will allow you the ability to extend the
mileage between changes without harming your engine. This will save you time and
money as well as helping to protect the environment by minimizing the amount of used
Do I have to use special oil?
The GM Oil Life Monitor System is calibrated for use with standard “Starburst” mineralbased
automotive engine oil. Synthetic oils are not required except for the Corvette.
Make sure to read the owner’s manual and select the viscosity and oil grade that is correct
for your engine. Any oil selected for use should carry the ILSAC “Starburst”.
How many miles can I expect to go between oil changes when using this system?
The beauty of the GM Oil Life Monitor System is that it will automatically adjust the oil
change interval based engine characteristics, driving habits and the climate in which the
vehicle is operated. For instance, mild highway driving in a warm climate will maximize
the interval between oil changes. Depending on the vehicle, this could be in excess of
7000 miles and as high as 12,000 miles. On the other hand, short trip driving in cold a
climate may limit the oil change to 3000 miles or less. In general, most people that drive
a combination of city and highway schedules find that the GM Oil Life Monitor System
will indicate an oil change every 7500 to 8500 miles.
What happens if I change oil and forget to reset the system?
Since the GM Oil Life Monitor System does not actually sense oil condition, it is
important that the engine computer knows when an oil change takes place. By enabling
the reset (read owner’s manual for instructions), it lets the computer know an oil change
has taken place. In the event that an oil change is done without resetting the system, the
‘change oil’ indicator will remain illuminated until the system is rest. The more miles that
are driven without the system being reset, the more inaccurate the GM Oil Life Monitor
System will be. If more than 500 miles have been driven after an oil change without
resetting the GM Oil Life Monitor System, the oil change interval should be defaulted
back to 3000 miles. After the oil has been changed and the system reset, normal use of
the system can be resumed.
The oil change service station recommends that I change oil every 3000 miles.
Why should I not believe them?
The 3000 mile oil change is very conservative approach to maintaining your vehicle that
dates back to 1968. Many advancements in engine and oil technology have been made
since then. These advancements, in conjunction with using the GM Oil Life Monitor
System, allow engine oil drain intervals to be increased without risking harm your the
I change my own oil, should I reset the system myself?
You can reset per the vehicle owner's manual, or ask your selling dealer.
Will I damage the car if I don't get the oil changed soon after the light comes on?
As stated in the owner's manual, change oil as soon as possible. It is recommended that
oil be changed within 600 miles of the change oil light / message.
Do I have to check my oil level now that my vehicle is equipped with the GM Oil
Life Monitor System?
Yes, the system does not sense oil level. As stated in the owner's manual, it is
recommended that you check your oil every time you stop for gasoline.
Will I void my warranty if I don't go by the GM Oil Life Monitor System?
Complying with the owner's manual recommendations will maintain the warranty.
I had my oil changed recently and now my GM Oil Life Monitor System light came
If the system was not reset (refer to owner's manual) at the time of oil change, the system
can be reset as long as it's been less than 500 miles since the last oil change. If this
mileage has been exceeded, change the oil at 3000 miles and reset system.
I prefer to have my oil changed still around 3,500 miles, what should I do?
It is ok to change oil prior to being notified by the vehicle. Be sure the system is reset
even if the GM Oil Life Monitor System light has not illuminated.
My oil seems dirty, I have 6,000 miles and no light, do I have a problem?
Discoloration will take place under normal conditions depending on driving conditions.
Refer to the Owner’s Manual for further information
Can any dealer other than my selling dealer perform Simplified Maintenance
While we like to recommend the selling dealer, any GM Goodwrench dealership can
perform the Maintenance I and Maintenance II service and reset the GM Oil Life System.
I use synthetic oil, should I expect to get more miles before the trigger point with
The GM Oil Life System is calculated based on the factory fill requirement. While some
benefits may exist, the oil drain interval is not extended due to the use of synthetic oil.
During Summer I drive my vehicle in a very hot climate, do I need to change oil
more often?
The beauty of the GM Oil Life System is that it calculates for severe climate use and
determines the oil change interval just as it does for trailer towing as well as stop and go
operation. There is no need to adjust the oil change based on climate, as well as vehicle
I continue to get 3,000 mile follow-up mailers from my dealer, what should I do?
Inform you servicing dealer that you prefer to go by the Maintenance I and Maintenance
II driven by the GM Oil Life Monitor System so that they may adjust the way you receive
follow-up mailings.
I have another GM vehicle a 2002 model with the GM Oil Life Monitor System, can
I use the Simplified Maintenance Schedule with it also?
While it is equipped with the GM Oil Life Monitor System, Maintenance I and
Maintenance II was not yet introduced. The proper recommendation would always be to
follow the owner’s manual.

05-05-09, 08:25 PM
Have you read up on it in the Technical Archives at the top left of this page?

EDIT: Oops. I guess you have. I have the Guru's explanation on how it works stored at home and can post them later if you'd like .

Mr 5.19.
05-06-09, 12:59 AM
I for one, would definitely like to see the Guru's explanation. :)

05-06-09, 08:36 AM
Considering that our retired "Guru" was a GM Powertrain Engineer, and the below quote (in Talamant's post) is extracted from the GM Northstar guidelines for oil life and maintenance, then his signature is buried in the text.

The trick is to read the FAQ quote and interpret the information. No one can state with certainty how your oil monitoring/changes should work because we all live and drive under different conditions. Nothing has changed except the fact that any of today's starburst designated oils will last far, far longer than a standard old wive's tale interval of "3000 miles". If you change your oil and filter and reset the OLM, then drive 1,000 miles to somewhere and 1,000 miles back, your OLM will show longer oil life remaining than if you drove the 2,000 miles under city conditions.

I've posted this before, but how many remember that the Kendall Oil Company logo of the fist with two fingers straightened stood for "Kendall, The two thousand mile oil" back in the 50's and 60's ?

05-06-09, 11:44 AM
OK, here it is in his words.

"One thing I can touch on and clear up.....the GM oil life monitor operation and my statement that ZDP (or ZDDP as you tend to call it here...most of the API literature just sticks to ZDP so I tend to use that) depletion is the basis for oil deterioration.

My spelling is poor but ZDP stands for zinc dialkyldithiophosphate which , as it sounds, is an anti-wear compound comprised of zinc and phosphorus.

ZDP is dispersed in the oil so as to be at a potential wear site if a surface asperity happens to break thru the oil film thickness causing the dreaded metal-to-metal contact. A molecule of ZDP must be present at that moment to prevent micro welding at the contact site which will cause material transfer, scuffing, scoring, wear and catastrophic failure. The concentration of ZDP in the oil will determine if there is ZDP present to work it's magic. The greater the concentration...the more likely a molecule of ZDP will be there...and vice versa.

By nature, ZDP is sacrificial. As ZDP is "used up" at a wear site to prevent micorwelding the concentration of ZDP decreases.... So...if you measure the ZDP concentration in engine oil in a running engine it will decrease at linear rate based on engine revolutions. Any given engine has a certain number of high potential wear areas where metal-to-metal contact could occur due to reduced film thickness and/or surface asperities....areas such as rubbing element cam followers, distributor gears, rocker arm pivots, push rod tips, etc...... The more of these areas, the more ZDP depletion. The more often these features come in contact the greater the ZDP depletion. That is why, generally speaking, ZDP concentration in the oil, for any given engine, will decrease at a fairly linear rate when plotted versus cumulative engine revolutions. The more times it turns the more contact the more chance for wear the greater the depletion. This is as much of a fact as I could quote ever and is really not speculation or anything. It is proven beyond a shadow of a doubt in many studies. That is why it is ONE of the basis for determining oil life remaining and why it is THE basic premise of the GM oil life algorithm. It is only ONE of the things that determines oil life...but it is the one thing that can be tied to engine operation in a linear fashion and estimated very accurately by accumulating engine revolutions via a counter.

The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.

You would obviously like to get the oil out of the engine before the ZDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.

The other things that determine oil life such a acid build up, oxidation, pentane insoluble’s such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDP depletion line.

The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life monitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.

The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.

One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don't believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.

Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.

There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDP depletion curve....in other words, zero percent oil life per the ZDP depletion is not zero ZDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDP is catastrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.

Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn't work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.

There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, and environmental groups all across the board. It is not some widget invented in a week and tacked onto the car."

Mr 5.19.
05-06-09, 12:04 PM
+ 1 Ranger.
Excellent post! :thumbsup: