Just before we sold our 2008 Pontiac G8 GT the oil change indicator came on. We had driven an amazing 13,000 miles without changing the oil. We were curious to know whether this was too long between changes or whether we could have kept rolling. We sent a sample of the oil off to Blackstone Laboratories to have them check the quality.
Here's what the lab had to say. And we also have some thoughts from our Edmunds engineering editor.
First, the report from Blackstone, which was emailed to us as a pdf. It lists all the trace metal levels and other technical data. But it also summarizes the report:
"13,000 miles on the oil seems to have worked pretty well for you. Copper, from brass/bronze
parts, was a bit high but with everything else looking good we just can't bring ourselves to get too upset about it. The average oil run for the GM 6.0L is just ~4,500 miles so your engine wears far better than most. You could try going a little longer but the excess wear metals make the oil abrasive and may limit how long you can go. Try 14,000 miles next time. The TBN read 1.5 so you still had some active additive left, though not much. 1.0 is too low."
We forwarded the report to Jason Kavanagh, Edmunds Engineering Editor and he had a few comments and explanations.
"TBN is Total Base Number, AKA detergency," Kavanagh reported. "Basically, new oil is inherently 'basic' in order to neutralize the acidity that is produced in an engine over time (that would be represented by TAN, or Total Acid Number).
"New oil has high TBN. Once an oil's TBN gets low, even if all else in the analysis is 'good,' the oil is essentially used up. It can no longer neutralize the acidity which, left unchecked, will damage internal engine components.
"It looks like 13k miles was fine for the G8," Kavanagh said. He went on to explain, "The copper and other wear metals are basically tiny bits of the engine suspended in the oil. Copper is from the bearings. Aluminum is the block/heads. And so on. Things like phosporus and manganese are part of the oil's additive pack. Basically, in UOA, you want these to be high, and the wear metals low."
So the verdict seems to be that the GM sensor accurately measured the effectiveness of the engine oil. Most of the oil was used up but not all of it. If we still owned the car, I don't think we would push the interval any higher. Going this long seemed almost like driving on borrowed time. Especially since many of our other vehicles seem to need new oil after only 7,500 miles.
I'm surprised that GM dealers aren't up in arms about this cutting into their revenue stream. A steady parade of driver's asking for oil changes is a nice chance to upsell them other services and boost dealership profits.
vt8919 says:
12:39 AM, 01/ 7/10
Pretty awesome! Looked at the site. Now I want to try it on my car's oil.
kevinlch says:
01:15 AM, 01/ 7/10
what oil are you guys using?
rayainsw says:
03:51 AM, 01/ 7/10
Interesting - thank you for posting this.
- Ray
G8 GT driver...
fundango says:
04:57 AM, 01/ 7/10
Good to know. My folks' M-B also recommends oil changes at 13k miles. After reading this entry, I feel a bit more comfortable telling them to stick with the maintenance schedule.
alex4515 says:
06:07 AM, 01/ 7/10
What oil was in the car? Also, for those that are interested, www.bobistheoilguy.com has some more great info including member's UOA results.
texases says:
06:28 AM, 01/ 7/10
Great post. I get tired of arguing with the 'gotta change oil every 3,000 miles, regardless of what the manual/computer/anybody says' folks. Nothing like cold, hard facts!
roadburner says:
06:44 AM, 01/ 7/10
I have Blackstone perform a UOA at every oil change of my 52,000 mile 2007 Mazdaspeed 3 as well as my wife's 88,600 mile 2004 X3 2.5.
On the MS3 I run a 5000 mile OCI using Mobil 1 5W-30, and I think that I could run it considerably longer. After one 5,400 mile interval the TBN was still 2.7 and most wear metal numbers were extremely low- for example, the copper number was 2 ppm while the universal average is 18 ppm based on a 4,000 mile run. I also don't have any problems with fuel diluting the oil, although a lot of MS3/MS6/CX-7 owners apparently do.
The X3 seems to be an outlier; the wear metal numbers are fine, but the TBN is at 1.0 or less by 8,500 miles- and that's using Mobil 1 0W-40 which is a BMW LL-01 oil. The SI system calls, for an oil change at @15,000 miles, but I'm not going to chance it. Right now I'm experimenting with Mobil 1 5W-40 to see if a more robust additive package will elevate the TBN number.
vt8919 says:
06:47 AM, 01/ 7/10
Well regardless, if you have a car that doesn't have this oil-checking system, it's probably better to replace the oil early than risking it.
hybris says:
07:10 AM, 01/ 7/10
If I could spare the money I would love to see where is my 160K truck is on oil based wear.
ahightower says:
07:11 AM, 01/ 7/10
Very interesting. I may have the same thing done on my own car. 08 Mazda3i (the 2.0 liter). I've been changing every 5K, per the owners manual (and because it's an easy increment to remember when due). Been using all synthetic, but different brands, whatever's on sale. I figure all name brand synthetics and higher end filters are good enough. I'm thinking of going to 7500 mile interval now that I've read so many things like this.
The other car is a GM (Yukon 5.3) and I just change whenever it says to. Nice to see further proof that the monitor can be trusted. It's been going about 6-7K, and lives a rougher lifestyle than my car. That's what makes me think the Mazda could probably do more than 7500. Probably will send off a sample to this lab before I change my routine.
redwoodaggie says:
07:21 AM, 01/ 7/10
Great information, thanks!
fuhteng says:
07:43 AM, 01/ 7/10
Very cool. Thanks so much for sharing guys.
throwback says:
07:52 AM, 01/ 7/10
"I'm surprised that GM dealers aren't up in arms about this cutting into their revenue stream."
Don't worry, my dealer still suggests 3k mile oil changes for my HHR-SS that uses synthetic oil. I am sure he is not the only one. I use the oil change indicator and change the oil when it hits 10% oil life left.
roadburner says:
08:24 AM, 01/ 7/10
"Don't worry, my dealer still suggests 3k mile oil changes for my HHR-SS that uses synthetic oil. I am sure he is not the only one."
My BMW and Mazda dealers have never pushed shorter oil changes than the OM or SI call for. My Mazda dealer does recommend a shorter change interval-30K miles-for the transaxle oil, but I think that's appropriate for a MT car.
bodyblue says:
08:42 AM, 01/ 7/10
In other words the engineers at car companies know what they are talking about and the 19 year old at Lube and Rape does not need to be listened to. I have two cars that I know the history of and one (my commuter car) that I have owned since it had 82,000 miles on it....I change the oil every 3500-5000 because it has 125K on it now. The other two I follow the man recommended intervals. The GM oil life sensors are great....why waste all of that money and create waste when you really dont need it?
cartester16 says:
09:02 AM, 01/ 7/10
Roadburner - BMW strongly recommends Castrol Full Synthetic, and not the kind you buy at Autozone. I've read that Mobil 1 is not a "full synthetic" and neither is the Castrol you buy at a retailer. Buy the stuff at the dealer - formulated specifically for BMW, and FULL Synthetic. Besides, at my dealer, it's even less expensive than Mobil 1 at Costco! ($5.50/qt). Give it a try, and let us know how it works or if BMW is full of ****. I go by my interval meter in a 325it and I just turned 150k, and motor still sounds & performs great with no leaks.
sgude says:
10:42 AM, 01/ 7/10
Although the monitor in my 325i sometimes has gone past 15K, I've always played it safe and changed it at 7,500. It helps that I've received half-off coupons from the great indy shop I use, so I don't really feel the pinch.
audisport says:
10:53 AM, 01/ 7/10
That's pretty good! I still get nervous about going 10k miles per change in my A4 especially since it's a turbo and I rev the hell out of it..
roadburner says:
11:00 AM, 01/ 7/10
cartester16:
Mobil 1 0W-40 and BMW's proprietary Castrol 5W-30 synthetic are both BMW LL-01 certified oils. Blackstone Labs(as well as several other engineers who have worked for oil companies and/or OEMs) do not believe the problem is the oil. See this thread:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Main=101065&Number=1357853#Post1357853
crowb says:
12:20 PM, 01/ 7/10
@ cartester16
Mobil 1 is a full synthetic oil using a PAO base stock. Castrol Syntec is by definition a full synthetic but I do not believe that they use any or as much PAO in their "over the counter/non-BMW German Castrol" Syntec. I think they rely mostly on a highly refined group III base stock. As does Pennzoil Platinum and Valvoline Synpower.
Regardless, by definition, they are all full synthetic oils. That definition was hashed out years ago when Castrol was sued by Mobil for claiming that certain oils were synthetic. Mobil lost and the looser definition has been adopted by most of the major oil refiners in this hemisphere when they make the stuff that goes into a bottle with "synthetic" on the label.
I believe that the European standards for a synthetic oil are stricter.
gregnv says:
01:22 PM, 01/ 7/10
one more reason to lament the removal of this car from our market : (
pontiaksolsice says:
01:33 PM, 01/ 7/10
While this is great that the car went 13,000 miles, I believe I read a post that additional oil was added, which would extend the lifetime of the oil. Either way it's still impressive.
joefrompa says:
09:23 AM, 01/ 8/10
Several comments:
1. Where's the full report? You should post it.
2. A TBN of 1.5 is too low to push to 14000 miles. I'd say the oil life monitor did it's job, but that oil was pretty much spent. I'd back it off 1,000 miles personally to leave more margin of error, since the oil life monitor is basing it's projections off fuel use and does not take into account: ambient temperature (which can enhance oil shear or contribute to oil acidity), quality of air ingested, quality of fuel, ambient humidity (which helps to contribute to oil acidity), etc.
Further, the oil life monitor does not assess the effects of any oil consumed or added to the sump. If you hadn't added a quart (say, on a car that didnt' consume some of which there will be a few), you'd probably have completely exhausted that oil.
3. Adding additional oil is a normal part of vehicle function for most cars that have long intervals. It does extend oil life, but that's part of what the long interval exists in the first place.
4. The average GM 6.0Liter that's been sampled for their universal averages is a truck engine with a far shorter oil interval duration and possibly much more severe use (truck duty). In other words, their universal averages are not very applicable here.
...
I ran my 06 Civic SI, whose oil life monitor reported a need to change at 6k, to 16.3k on Amsoil SSO 0w30 before changing and getting a blackstone report identical to this. it showed the engine oil could've gone to 18k or beyond easily. And I definitely drive very hard.
Oil life monitors are good for OEM-style oil and generic driving conditions (i.e. 15k miles a year, normal ambient conditions). As the driving conditions start to change, it's important to realize that their effectiveness starts to become more in question.
That being said, OLM's are usually a bit conservative.
estreka says:
03:20 PM, 01/ 9/10
Great site! I'd love to know the oil life of my car. Forced induction cars can be so difficult to determine, especially when the car didn't come FI. I usually change it when I note a change in performance.