Relying On Computer To Indicate When Oil Change Is Due

[DTS419]

I just saw in my owner's manual it says the computer will tell me when it's time to change the oil. Now I can't help but be skeptical of this feature... Can the computer reliably and consistently detect when it's time to change the oil, or am I better off just changing every 5,000? Anyone just change the oil when the computer says to do so?

[beboswell]

I absolutely rely on the computer to tell me when to change the oil. The fact is, we have probably all changed our oil too frequently in the past just to be sure. Today's onboard computers are so sensor rich that they know how hard the engine is working and therefore how long your oil should last. The only exception would be if you are operating in especially dusty or dirty environments, but that's not many of us. I used to run a fleet of about 80 vehicles, and these oil life monitors saved us thousands without costing one extra cent in repairs over hundreds of thousands of miles.

[CapitalTruck]

Do a search on this topic and you'll see how all the different members of the board feel about this.

[pwall]

I have to admit that I rely on the computer.

At 80+ for an oil change......

[bill190]

Here it is...

 

All about "zinc dialkyldithiophosphate" and the GM "Oil Life Monitor" (change oil light) from "Bob is the Oil Guy"...

 

http://www.bobistheoilguy.com/forums/ubbth...p;Number=130037

[2007VictoryRed]

I do not Trust the computer. I change my oil every 3,000 miles no matter what. I just fell better when I do.

[beboswell]

UH YEAH, what Bob said

[brims]

At $50 an oil change, I too rely on the computer, down to 10%. That will go up a little if/when I put in an engine oil cooler.

[msu33]

$50 bucks? Wow....I guess thats why I change my own oil. I can change the oil and replace the filter for around 20 bucks. I change the oil in my 01 every 3k miles.....Not sure what Im going to do about the 09. I will probably change it every 4 or 5k......maybe stay with 3k, cause thats what im use to.

[georgecdisc]

$50 bucks? Wow....I guess thats why I change my own oil. I can change the oil and replace the filter for around 20 bucks. I change the oil in my 01 every 3k miles.....Not sure what Im going to do about the 09. I will probably change it every 4 or 5k......maybe stay with 3k, cause thats what im use to.

$50 doesn't sound too far off to change it one's self. $20 though? $5 filter, leaves $15 for oil. That is $2.50/quart of oil. I don't see this around very much, let alone a synthetic.

[crepitus]

i do a synthetic oil change for $28. Bought a case of Napa gold filter from ebay. $3 each. 5 qt jug of Pennzoil Platinum $20 at wally world and 1 extra qt is $4 and change.

[redvett]

Here is OLM info from BOB the oil guy.

Topic: ZDP depletion and GM oil life monitor

bbobynski

Member

Member # 6738

 

Icon 1 posted Profile for bbobynski Email bbobynski Send New Private Message Edit/Delete Post Reply With Quote 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 microwelding at the contact site which will cause material transfer, scuffing, scoring, wear and catostrophic 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 sacrifical. 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 cummulative 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 premis 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, petane insuluables 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 montitor. 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 catostrophically 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, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car.

 

The oil life monitor is not under the control of a summer intern at GM Powertrain per an earlier post....LOL Not that a summer intern wasn't compiling calibrations or doing a project on it but is under control of the lube group with a variety of engineers directly responsible that have immediate responsibility for the different engine families and engine groups. The idea that a summer intern was responsible for or handling the oil life monitor is ludicrous.....LOL LOL LOL

[Bill in Niantic]

I asked my Dealers service shop what they use for oil changes. He said Mobil Oil and GM Delco Filters. I don't think it's M1, but Modil Dino.

The dealer charges $10.95 per oil change, no appointment required.

I was planning on putting in the drain valve and switching to Royal Purple 5/30 w/K&N filters.

 

My last car I used a Canton Racing Filter < http://www.cmfilters.com/spin-on.cfm > w/Royal Purple and 4 oz of Militec 1. Also had an Oil Guard by-pass Filter.

 

But heck, for $10.95 per Oil Change, with a Delco Filter and Mobil oil, I might just stay with that. I don't even get dirty.

 

[SparkySparks]

My truck came with 3 years of oil changes every 5,000 miles so thats when I get my oil changed. The computer said I had about 20% oil life left.

[DTS419]

How do you check the computer's estimate of percentage of oil left? My owners manual says that it has the oil sensor and my instrument panel has the "message center"... will it just flash an indicator that oil change is due, or can I see a percentage?