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Discussion Starter #1
Can anyone shed some light on how the Volt determines remaining oil life? The manual says that the oil should be changed every 24 months, or when the "Change Engine Oil Soon" message is displayed. The remaining oil life percentage has been steadily declining for the month that I have owned my Volt, like the decrease is in proportion to the miles driven. However, the miles driven have almost all been using the EV mode.

I'm thinking that the remaining life percentage decline is based on time in my case, rather than miles or gasoline use. I have owned the car for 1 month, and the oil is supposed to be changed every 24 months. 1/24 = 4.2% and my remaining oil life percentage right now is 96%. If my theory is correct, just parking the Volt for a month without driving it should result in a 4% decrease in the Remaining Oil Life percentage. This isn't a bad thing, because if correct, I wouldn't have to track how many months it has been since the last oil change.
 

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I would expect that the oil life would be a combination of time and miles driven. Obivously the more miles driven the faster the oil life would drop. I calculate ~1% per week (1/(52*2).

I have had my Black volt for 8 weeks and driven 719 miles on gas (1871 total) and the oil life is at 91%. This would imply that it is mostly time based. Still at 83 mpg lifetime though. The 360 mile drive home has killed my mpg. My Red volt is at 137 mpg lifetime.
 

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A past story stated that the Volt will recommend you change your oil at least once every two years, so you're probably seeing the "time-based" oil life tick down.

I'm at 89% oil life at 2253 miles, with 1152 miles on EV.
 

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We've had our Volt for almost 3 weeks and the oil is at 94%. That due to the 1300 mile trip back to Florida from NY. Total miles 1560, ev miles 279. That also killed the overall mpg. It'll take awhile to get over the 46 mpg we have now.
 

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Assuming Chevrolet is using the same algorithm in the volt that they use in other cars, the oil life remaining is based on a number of factors including the following (there may be others I don't know about):
Time since last reset
Number of Engine Revolutions since last reset
Engine Temperature
Average Engine RPM
Engine RPM fluctuations

As you can see there are factors to calculate effect heavy vs. light loads and constant vs. stop-and-go speeds. I know from Chevy trucks I have owned the remaining oil life drops faster on a % per mile basis when towing than it does when driving empty. On the Corvettes it drops faster on a race track than cruising on the freeway.

It is a great tool! Just reset when the oil is changed and you never have to worry about when your next oil change is due, the car will start to remind you at 10% remaining. OnStar will keep track of it and graph the history as well.
 

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adamsocb,

Yeah, it's a pretty sophisticated tool. It took me awhile to accept how long the intervals were, as I was raised on 3000 miles. But we use synthetic in most of our vehicles, so I think that gives us a bit of a cushion. The interval on my Cobalt has been almost 10K miles, but it does see a lot of freeway commuting.
 

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As others have said, it's an integration of a lot of factors including time.

On our "normal" vehicles it tracks real well with average speed. High average speed=lots of highway miles=10K change interval. Low average speed=lots of local miles and cold starts=lower change interval.

Pete Foss
GM R&D
 

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Hey sorry to be bringing a old thread back from the dead, but it's relevant to my issue.
I got my Volt on Jan 28 2011, when the remaining oil life was at 99% and the odometer said 85 miles.
I figure there are 2 ways the oil life remaining is calculated, both count down from 100%, one is by time alone since last reset, and the other is closely related to the number of CS miles on the engine since last reset (among other related factors), and whichever of those numbers is lowest is what it reports to you.
(Am I correct so far?)

I have put all the numbers from my monthly Onstar email reports into a spreadsheet and figured what it should be reporting based on time alone and also by CS miles. I figure that by 2 years time, it should be down to 0%, so that means by considering time alone, the report I got today should indicate 63%.

And for the CS miles, my Volt's odometer says 13,029 and 5,889 of those miles are CS. Literally half of those CS miles were driven 2 weeks ago. I don't know how many CS miles should be considered time to change the oil, so if we assume it is around 6000 miles, then I should have 2% oil life remaining.

Something is wrong with the indicator in my volt because as I look on the spreadsheet of what the remaining oil life reported is each month, it closely matches what I expect based on time alone up until 2 reports ago. The previous report it stayed at 69% when based on time alone it should have been 67%. On today's report, it was still 69%, but based on time alone it should be 63%. And if you consider miles driven on gas, I would think it is time to change the oil by now but somehow it got stuck at 69%. It may have happened when I took it in for the software update.

So what do y'all think? My question for you is have you observed the oil life remaining indicator change more rapidly when you put a lot of gas miles on your Volt? And how rapidly does it decrease per gas mile driven? And has anyone brought their Volt in for their first oil change yet?

I will probably bring mine to the dealer soon for an oil change if it seems to be ready for one, and have them see if a warranty repair is necessary to get the oil life remaining indicator to work properly.
 

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I don't know how many CS miles should be considered time to change the oil, so if we assume it is around 6000 miles, then I should have 2% oil life remaining.
I think here is the error of your ways. The Volt's oil is a long-life synthetic. I've got over 25K miles on my Volt (which obviously isn't a year old yet). About half of that is CS miles. My oil-life indicator is around 35% I think.

You are correct in that the oil should be changed every two years, whether you use if or not. That's even in the owner's manual. If I were to keep up my current rate of adding miles (which I keep saying is unlikely, but really... other than trips around the state I don't think I have any more big trips before summer '12 - well... Maybe a third trip to Texas, but other than that... :- ), I don't think I'll need to have my oil changed until around 36K miles on the odometer. Maybe a bit more.

I've heard some have had their oil dutifully changed at 7.5K miles, when they rotate their tires. If you don't mind helping send your dealer's kids through school, you certainly won't hurt your car doing so yourself.

Otherwise, I don't think there's anything wrong with your oil life predictor. It sounds like it's working fine.
 

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And for the CS miles, my Volt's odometer says 13,029 and 5,889 of those miles are CS. Literally half of those CS miles were driven 2 weeks ago. I don't know how many CS miles should be considered time to change the oil, so if we assume it is around 6000 miles, then I should have 2% oil life remaining.
As Rusty points out, the synthetic oil gets a longer life. But there's another factor to consider: during those 5,889 miles of CS driving, the engine was on perhaps 50% of the time. So that's the equivalent of a gas-only car going <3,000 miles.

I cannot, however, explain why the % would not go down over the course of a month in your case.
 

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I believe it is because the algorithm is smart enough to realize that some of the decreased oil life just for time is overlapped by your CS miles and not double counted. On regular non hybrid GM vehicles, I routinely go 10 or 11K miles before it calls for an oil change.

Pete Foss GM R&D
 

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Just guessing, but since short runs tend to add moisture to the oil which is bad, the long trips that you took would have dried out the oil, and may result in a longer life expectancy.
 

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Just wanted to add in my own observations here - I've had the car for about about a month and a half. When I got it, it had 220 miles on it (delivery) and oil life was at 98%. I have since added another 800 miles, but all were EV only with the exception of maybe 2 miles total during 15 deg temps (causing it to use the engine for warmth). At the moment, my oil life is still at 98%. So if there is a time (only) impact, it's very minor. If you don't use the engine, don't expect to be changing oil very often. Also note that all of my outings are short (5 miles typical, with an occasional 20-25 mile trip thrown in for fun).
 

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I think I have some very interesting to add to this thread. Like some earlier posters here, I had been surprised to see that my oil life was continuing to go down pretty much independent of whether I was running the engine or not. My daily driving is usually purely electric, and the oil life would still tick down, slowly but consistently. After road trips, I would that it was still ticking down at about the same rate despite the near-constant gas mode usage. I graphed my oil life history (from the highly recommended voltstats.net) and indeed it was a nice smooth slope, with seemingly little correlation to gas engine usage.

Others have said that it was a combination of factors, but it sure as heck looked to me like TIME was the ONLY factor.

Well, here's the interesting part. Today I was interviewed (about my Volt and EVs in general) for a TV show, so in preparation for that I took a long look at my Volt's performance using the voltstats.net data. When I graphed the oil life, I found that the usual steady slope had continued down until around 01-Dec-2011, when it suddenly leveled off.

Guess what happened on 01-Dec-2011? I got the software update for my 2011 Volt! It looks like the software update changed the logic of that oil life counter. See the attached graphic.

You'll also notice the "step" in the graph in Sept 2011 -- that's when I was out of the country for two weeks and the car was parked. Notice how as soon as I started driving it again, the oil life counter dropped right down back onto the slope! That tells me it is clearly time based. Well, it WAS, because since the software upgrade it has leveled off. I drive in gas mode only once every week or two, and then usually for just 10-20 miles or so.

FYI, the other data in the attached graph is tire pressure. You can see where I filled up the tires just before Thanksgiving.

As an aside, if you haven't registered your Volt at VoltStats.net, my god go do that right now! It really enhances your ownership of the Volt, and is what GM should be doing with MyVolt.com but doesn't seem to ever actually get around to. Note that you can download all of your data, i.e. as a CSV file, that you can then import into a spreadsheet program (e.g. MS Excel). That's how I created this graph.
volt-oil-life.jpg
 

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Just want to put it out there that on my 2012 the oil life counter DOES NOT go down unless my engine is running.. I have 3779 miles on mine, 3108 of them electric, and my oil life indicator is at 96%. I look at it everyday on my Onstar RemoteLink app, and it is always at 96%. Granted my engine ran in maintenance mode last week for the 10 minutes and it still stayed at 96%. To me it shouldn't go down unless the engine runs, and it looks like I will hit the 2 year mark with well over 80% left.
 

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Discussion Starter #16
This is interesting. But doesn't GM recommend that the oil be changed every 2 years regardless of engine use? If that is true, then isn't elapsed time the best indicator for oil life? I understand that even synthetic oil degrades over time and needs to be changed even though the engine isn't being used.
 

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Assuming that the oil should be changed at least every two years, note that the slope I saw prior to the upgrade was in fact that rate. Expiring in two years would mean about 4% loss of life per month, and that is exactly the slope in my graph. With it flattening out now, it wouldn't hit 0% at my two year point unless I started using a lot more gas, or perhaps some extra end-of-life logic kicks in.

I don't understand yet how this works, but I guess by 11 months from now I probably will!
 

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There are reasons to change oil other than it breaking down - and I really doubt syn oil breaks down much with just time (though any additives are another story). Especially initially, the engine wears more during break-in, so you have metal particles in the oil and most of those get in the filter. But it's kinda tough to change a filter without changing oil. A low use engine will also have water from both blow-by and plain old condensation from temperature cycling collecting in the oil and you don't want to have semi-conductive mayonnaise in your crankcase promoting corrosion. The volt engine may not reliably run enough to boil out all the water in the crankcase - that usually takes a good half hour at high power to get done.

Not sure how GM handles this engine, but on a couple of other new GM cars I've had recently - a 2010 Camaro SS and a 2012 Cruze (with a similar engine) I noticed that the initial oil was pretty thick stuff - as if it still had the assembly lube in it (that thick stuff you put on cam lobes at assembly so things don't get ruined on initial startup rotation before the oil pump and push oil around). Don't know what the factory does, but any engine re-builder uses some assembly lube, and it's like molasses so it will stay on things till the real oiling can take over. Kind of like STP, very thick stuff.

Since there's no way that improves gas mileage...but you want to get all that initial wear metal over and done with, I compromised on both of those cars and changed the oil early, but not too early - about 5k (hard) miles in those, when the oil life indicator said about half life. I used 5w-30 synthetic as the replacement.

I was astonished at the sudden change in performance I got when I did that in both cars. It's as if the engine control computer noted the change and re-calibrated to let me have more - it was almost like putting in an after-market chip. Gas mileage also improved.

Perhaps some GM engineer can chime in and explain what I experienced - but I did notice (and so did my wife) a very definite change in performance right then which wasn't a fluke - it stayed, and on two very different engines. The new oil felt thinner on the fingers using the dipstick to sample it than the original stuff did.

This is interesting, but frustrating, because it's going to take a long time to get the equivalent of 5k miles on the Volt's ICE...and it was a significant enough change that I want it! But I also want the engine broken in first, so that oil and filter change removes all the little metal bits that result from doing that.
 

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FYI, GM has said that for the Volt they take care of the break-in period and oil change during the mfg process.
 

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An update to my long post above (with graphics!), where I saw the "oil life remaining" counter stop moving after the software update ...

It still hasn't moved! For nearly 6 months now, it has stayed planted at 52%.

My oil life remaining counter has been "stuck" at 52% since 01-Dec-2011. Prior to that date, it was gradually decreasing at a rate of 4% per month, regardless of miles driven; I typically drive very few gas miles, maybe 20-50 per month. After that date, it stopped counting down even that much; it has ticked down a tiny bit over the last 6 months ( 52.9% -> 52.5% -> 52.1% ) but that is not enough to match the time-based decay one would expect. I've driven only 200 or so gas miles in the last 6 months, but I still would expect the oil life countdown to continue.

I called the Volt Advisor team this afternoon to ask about this, and they have nothing in their database about any problems with this counter So it may very well be normal, but sure does seem suspicious. Will the life start to accelerate down again as I get closer to the two year expiration point? That seems like a weird way to do it, especially considering the nice-n-simple linear behavior it had before. My two year anniversary is 7 months away for me.

The Volt Advisor suggested I bring the car into the dealer, but that's quite a hassle for me, and further what exactly am I going to complain about? My experience with the dealers that I need a pretty clear, specific problem that needs addressing for them to do something about it.

Anybody else have a frozen oil life counter?
 
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