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Old 01-01-2007, 03:23 AM   #1
DonandBonnie
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Duramax Oil Changes

My new 2007 Silverado with the Duramax does not specify mileage intervals for oil changes. Instead there is a dash board display that shows a percentage of the engine oil life remaining. I currently have about 725 miles on the odometer and the display shows 94% of the oil life remaining.

Does anyone know how this system works? If the display percentage is determined by reading the quality of the oil, then perhaps a synthetic that allows extended oil changes might be in order. If however it is only geared to the odometer, then any good grade oil would probably work.

The truck comes with a one year free subscription to Onstar. In addition to the emergency services available, they send me a monthy email with diagnostic checks on the truck and will call immediately if they detect a serious problem that requires immediate attention. On my first mileage check, I got 15.3 MPG.
 
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Old 01-01-2007, 03:45 AM   #2
OntMont
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I have the same truck (except for OnStar). I wondered the same thing because I am around 20% life.
I doubt it can monitor oil quality, but it is probably more than just distance travelled. Probably more like engine revs turned, or some combination of factors collected by the engine computer. My older Duramax had different oil change schedules for heavy and light use (e.g. towing was heavy duty use). I would think that there is something built in to account for this. (maybe related to use of the tow/haul mode).

In short, I don't know either, but since it is GM who have to fix the engine if it goes wrong, I'm going to trust it until proven otherwise. I don't think I will use synthetic oil in the engine. I probably will in the Allison.

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Old 01-01-2007, 04:02 AM   #3
nailbender
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My son has a 05 D/A that has the in dash oil display. He had 9000 mi on the truck before first oil change and the the display indicated the oil was still good. He took the truck in for other service work, and the service manger gave he a lot of trouble for not having the oil changed at 6000 mi.
The Onstar is a great system, wished Ford had it.
Congratulations on the new truck and when you get the Montana, you will have a great rig.
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Old 01-01-2007, 04:57 AM   #4
Clyde n Deb
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I have about 50k on my 04.5 D/A now. I took the advice of some customers of mine that specialize in diesel work, and combined it with my old gasser habits. I run regular 15w40 Rotella, and do not exceed 5000 miles between oil changes. I did go to synthetic in the tranny, t. case, and front and rear diffs. (Rear diff has synthetic from the factory). New Allison has different fluid again............not sure where they're at yet on approved synthetics.
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Old 01-01-2007, 05:14 AM   #5
Bill and Ann
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I change the oil when the computer tells me to change it. The service manager at my dealer told me that's what it is for. He said I was wasting money by changing it any sooner. It is usually between 10000 and 12000 miles.
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Old 01-01-2007, 05:30 AM   #6
ken
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We have the 05 Duramax and we change our oil around every 4,500 miles. We use the Valvoline priemere blue oil. Our dealer also gave us the Valvoline 200,000 mile warranty on the engine. The oil was developed by Valvoline and cummings diesel. Millage not towing is over 20 mpg and around 13-14 mpg towing the Montana.
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Old 01-01-2007, 06:47 AM   #7
OntMont
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I checked in my owner's manual, and it says that the oil change interval is determined by the engine computer based on a combination of engine revolutions and oil temperature. The filter change indication seems to be a separate thing that only appears on trucks with the steering wheel controls for the Driver Information system.

I felt more comfortable with a stated oil change interval, but the revolutions & temperature approach makes sense to me.

BTW, for the 07 Classic models it says to use 5W20 GM approved oil only. With the cost of these vehicles, I am going to go "by the book".
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Old 01-01-2007, 07:41 AM   #8
Glenn and Lorraine
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GM's recommended oil change on my 03 Silverado and now on my 05 Sierra, both with the Duramax, is every 10,000 miles. Since it is GM that is is covering the warranty I will follow their guidlines 100%. I also use the GM recommended oil that is supplied by the dealer that is servicing my truck.
Back when I had a gasser I changed oil every 5,000 miles but if GM wants it every 10,000 who am I to argue with the experts.
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Old 01-01-2007, 08:42 AM   #9
Cat320
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My dealer swears by the DIC and says to follow the maintenance intervals noted there. However, there is more to it than that...if you read the fine print, using oil changes for example...it says to follow the DIC, but do not go over a year without an oil/filter change, regardless of mileage.

To add to the confusion, GM says to service the Allison spin on filter at the first normal scheduled service as noted on the DIC. However, the Allison site says to change the filter at 5,000 miles.

I just turned 5,000 and changed the eng oil/filter and the Allison spin on filter.

OntMont...check your Duramax supplement to the owner's manual...the recommend oil for the Dmax is 15w40 (I think you'll find 5w20/30 is for gas engines). Whatever you use be sure it has the "CJ-4/CI4" recommendation...the C rating is for diesels.
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Old 01-01-2007, 09:13 AM   #10
Montana Sky
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I run 3,000 mile oil changes on my Duramax. I have the Oil Life feature on my DIC, have never followed it since day one. If I am on a road trip with just the truck (no towing) I will run the oil to 5,000 miles between changes. Otherwise I stick with 3,000 miles. I only have GM shops work on my truck so the oil is what ever they use. I will be rolling 70,000 miles sometime in Jan. You are not going to see your best fuel mileage until you get that motor broke in. My average in town mileage has been 17-18 mpg and my highway has been 21-22 mpg.
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Old 01-01-2007, 11:02 AM   #11
Mac
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OntMont,

I was going to say the same thing that Cat said, the Classic 07 is the same recommendation of 15/40 and I think he's right it's in the supplement. As for me, I think I'll go the 5000 mile route for oil changes, I would rather "waste" a few bucks here and there and be on the safe side.

mac
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Old 01-01-2007, 11:54 AM   #12
illapah
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Actually, if you want to really know if you are on the right schedule, send in a sample (or few) for analysis. Not that expensive and could be an eye opener to our customary oil change thoughts. I probably go for the longer intervals.
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Old 01-01-2007, 11:57 AM   #13
illapah
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BTW, here is one lab to consider:

http://www.blackstone-labs.com/index.html

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Old 01-01-2007, 11:57 AM   #14
markwick
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I don't have a problem with GM saying stick to the Driover's Information System (DIS) and change the oil when the system says so. It would probably save a bit of money - HOWEVER - if there is going to be any problems caused to the engine and parts by not changing the oil as frequently as every 3000 towing or 5000 regular driving, these problems will not show up until well after the warranty has run out out. The Duramax is a great engine - should last 250,000 to 300,000 if looked after. For my money I will stick to the 3000 and 5000 mile changes - If the Duramax really does not need new oil at that time it still can't do any harm at all to put in fresh oil. I intend to keep mine for a long time. For my peace of mind I will continue to keep to my own oil change schedule. I don't profess to be an expert on this but at least I feel good even though I may be wasting a few $'s per year.
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Old 01-01-2007, 01:05 PM   #15
Illini Trekker
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I follow the school of 5000 mile oil changes. If it were me I'd change at the first 1000 mile to get that new oil OUT. With the new engine and the metal wearing in, IMOE it would be best to change the filter and oil and start the engine with the oil you'll run from now on out.
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Old 01-01-2007, 04:20 PM   #16
OntMont
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Thanks Guys, looks like I made a mistake and read the gas version of the manual. Please everybody, do whatever the owner's manual for your particular year, model, and engine says!

John.
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Old 01-01-2007, 10:12 PM   #17
cmp-shooter
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3 to 5000 for mine, I get the shell rotella for free
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Old 01-02-2007, 03:52 AM   #18
ARJ
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I have spoken with quite a few folks both at dealers and at my local freightliner dealer about frequency of oil changes. The consensus is 3k miles even if using synthetic (this applied to 18 wheelers too from what I understood). The reason I get is because of the crap in the oil rather than the oil breaking down. I suppose one could change only the filter and extend the change cycle. However, the price of oil vs the price of an engine is enough to convince me to stick with my 3k interval.
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Old 01-02-2007, 05:32 AM   #19
illapah
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I found this on the Blackstone lab web:

Do I Need a TBN?

What is a TBN, and who uses it? In short, a TBN (total base number) measures the amount of active additive left in a sample of oil. The TBN is useful for people who want to extend their oil usage far beyond the normal range.

By comparing the TBN of a used oil to the TBN of the same oil in virgin condition, the user can determine how much reserve additive the oil has left to neutralize acids. The lower the TBN reading, the less active additive the oil has left.
(Note: You only need to send in a sample of virgin oil if you want to know exactly where the TBN of your specific oil starts out. The TBN of most gasoline engine oil starts around 8 or 9. Diesel-use TBNs start around 11 or 12.)

An oil's function is to lubricate, clean, and cool the engine. Additives are added to the oil to enhance those functions. If the oil becomes too acidic, it will corrode the engine. A good TBN result, meaning plenty of active additive is left in the oil, is usually in the 6.0 to 14.0 range (depending on whether the oil is for gas or diesel engines). A low test result, meaning very little additive is left, is down around 2.

Scientifically speaking, the TBN is one of two "neutralization number" tests run on oils. The TAN (total acid number), which is used for hydraulic oils, is the other. The TBN measures the total basedity of an engine oil; that is, how much base (as in, a base vs. an acid) additive is in the oil to offset the deleterious effects of acids coming into the oil from combustion and other sources.

However, the TBN is not the only factor to consider when determining how long an oil can be used. If wear accumulations and insolubles in the oil build up and become abrasive, we would recommend changing out the oil, no matter how high the TBN reading.

Case Scenarios

Case #1
Joe Owner has a new engine and wants to determine how long he can keep a fill of oil in place. He sends in a sample of his virgin oil (with no miles on it) and a sample of his used oil (with 3,000 miles on it) for an analysis and a TBN test.

The virgin oil has a TBN reading of 12.0. His used oil has a TBN reading of 9.5, and his wear levels are fine. Joe decides to leave his current fill of oil in place, and resamples in another 3,000 miles. This time, the TBN reads 6.0, still an average amount, but his wear accumulations and insolubles have built up to a level that causes the oil to become abrasive. We recommend that Joe change out this oil.

Case #2
Jill Owner has a new engine and wants to determine how long she can keep a fill of oil in place. She sends in a sample of her virgin oil (with no miles on it) and a sample of her used oil (with 3,000 miles on it) for analysis and a TBN test.

The virgin oil has a TBN reading of 7.0. Her used oil has a TBN of reading of 5.0, and her wear levels are fine. Jill decides to leave this fill of oil in place, and she resamples in another 3,000 miles. This time, the TBN reads 4.5, and her wear levels are still low. Jill decides to leave her oil in place a bit longer, and she resamples in another 1,500 miles. This time, the TBN reads 2.5, and although wear accumulations are still normal, we recommend she change out the oil.

Do you need the TBN test in your maintenance routine? Only you can answer that question. We offer a TBN test on any gasoline or diesel oil sample for an additional $10.
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Old 01-02-2007, 07:50 AM   #20
Montana Sky
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A test sample is $10? In Case two scenario Jill sends in her original $10 and sample in, tests fine. She resends another sample and $10 in 3,000 miles, test fine. She then sends in a 3rd sample and $10 in another 1,500 miles, they tell her to change her oil. If I understand this correctly; Jill has spent $30.00; more than half the cost of an oil change to have someone tell her she needs to change her oil. Wouldn't she have been better off to just pay the dealership $58 at the 3,000 mile interval and have her oil changed instead of spending $30 to have someone tell her to change her oil and then going down to the dealership and paying the original $58 for her diesel oil change? Sounds to me like Jill got ripped off; well at least paid $88 for an oil change. Am I missing something here??
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