Filed under: Maintenance, Green, Tech
Determining oil change intervals via analysis
by Eric Bryant on Aug 2nd 2006 at 4:04PM 
John's post on Valvoline's oil change interval survey results got the attention of our readers, so perhaps now it's time for a slightly different perspective on the topic. If one accepts the fact that each combination of driver and engine is likely to require its own oil change interval, then the idea of some sort of "blanket" recommendation on the topic seems almost silly.
With this in mind, we decided to run some analysis on a couple of vehicles in our motor pool. Due to the mileage put on our 2001 Honda Accord V6 during its daily commute, the 3,000-mile interval suggested by ASE Master Mechanics would require a change every month and a half. The service manual, on the other hand, suggests that the oil need be changed only every 8,000 miles - an interval a bit more practical for busy DIYers. A couple simple and affordable tests from Blackstone Labs offered some insight on who might be right. And what sort of stress does the high-revving stroker V8 in our Impala SS impart upon its oil? Click through to find out.
The sampling process is simple enough - just use one of Blackstone's free kits to grab a few ounces of oil during your next change. It's best that the sample be taken from somewhere in the middle of the drain process, and obviously a bit of caution is required if doing this if the engine has been recently run. Next, fill out the necessary information on the included paperwork, including the make and model of the car, the type of engine, the brand and weight of oil, and the number of miles put on the vehicle since the previous oil change. Include the necessary payment ($30), and drop it in a mailbox. Blackstone analyzes the oil using inductive coupled plasma (ICP) spectrometry, and in about a week, the results will show up in your inbox (or snailmail box) looking much like this [click on the photo for a larger version]:
You can see here that results will show the levels of a variety of elements (additives and contaminants), some physical properties of the sample, and some commentary from the lab. Additionally, the element levels from previous samples are shown, as well as averages from that testing, and averages from other users who have the exact same type of engine.
In this particular case, we're looking for any signs of excess wear, which would come in the form of elevated levels of iron, aluminum, lead, and copper. While the sample from 5/1/05 shows some wear results that are slightly above average, the results from the 9/11/05 test are actually a bit less than average, even after 8,700 miles of usage. Additionally, the Total Base Number, or TBN (an indication of the oil's ability to neutralize acid) is low but still safe at 2.1. The subviscosity and flashpoint were also within the acceptable range for this oil viscosity. While Blackstone states that it may be possible to run this oil change out to 9,500 miles, we'd probably consider the factory recommendation of 8,000 miles to be just about right.
Castrol GTX 5W20 was used for the first test, while Valvoline 5W20 was used for the second round of analysis. This doesn't necessarily mean that the latter should be called a better oil, but it does seem better suited for this particular engine.
Obviously, each engine, driver, and environment will have different effects, and that doesn't even include the variables that we can add with all the different oils and filters that are available on the market. Some experimentation will be required to determine the optimum change interval for any particular car, and it's always going to be better to err on the side of caution until sufficient data has been accumulated.
So, what about our resident hot rod?
We run Castrol 20W50 in this engine to give it just a bit of extra protection at high revs and temps, and yet the subviscosity was below the expected value after only 2,600 miles. We've been trying to maintain a change interval of about 2,500 miles on this engine (which works out to be once a year), and that seems about right.
Due to the relative newness of this engine, we're not yet worried about the high levels of iron, but we will be looking for that to decrease over time. The copper and lead look good, so we're not in the process of wiping any bearings. One can also note the high level of silicon in this sample, although this is likely explained not by contamination by dirt but rather the use of silicone gaskets and RTV silicone sealer that was applied during its most recent reassembly. We were definitely happy no fuel dilution had occurred, despite the fact that this engine tends to run a bit rich while warming-up.
Hopefully we've demonstrated the value of oil analysis. We certainly regard it as a good value, and will continue to utilize it on the large variety of engines that we maintain here at the Autoblog Garage.
_opt_thumbnail.jpg)
Reader Comments (Page 1 of 1)
Jason 4:24PM (8/02/2006)
If this sort of thing interests you, read this also:
http://neptune.spacebears.com/cars/stories/mobil1.html
Reply
johdaxx 5:27PM (8/02/2006)
Excellent Work! The above linked article makes a good point, even a snapshot analysis isn't as valuable as the trends that arise over time. It will be interesting to see how the Autoblog cars pan out. In my experence the values will fluctuate over time, just like the living breathing thing each engine is.
I'm amazed that the SS beat up its oil as quickly as it did, though - yikes!
Reply
Perry 5:37PM (8/02/2006)
The Silicon and Molybdenum are likely from your pistons. You probably used a coated Hypereutectic piston in the rebuild, right? The coating is Molybdenum. Hypereutectic pistons have 18% silicon IIRC.
Reply
T. Fowler 6:08PM (8/02/2006)
It would also be interesting to see a test of a Bypass Oil Filter on oil quality / degradation. The manufacturers *claim* that bypass oil filters can significantly increase oil change intervals. Independent verification (or disproval) of those claims would be very interesting.
Reply
mehool 7:04PM (8/02/2006)
great post Eric! I find your posts to be some of the most useful and interesting on the blog, so keep it up.
Reply
Jim D. 8:16PM (8/02/2006)
While this information appears helpful, it is still impossible to really know which oil and viscocity combination is the best for your particular car without numerous trials and errors. And even then, will your normal engine "break-in" period negate those results? Probably.
If you want to skimp on oil change intervals, be sure to use a more proven oil, such as full synthetic in order to preserve oil properties for longer periods of time. Also, a quality filter (not the orange one) is extremely important.
In my opinion, take my advice, spend more for synthetic oils and quality filters and save your $30 per trial test.
Reply
laserwizard 8:21PM (8/02/2006)
My latest car which I've had since it was new has been on the manufacturer's suggested interval of between 4,000 and 7,500 miles - the more highway driving I do, the longer I wait for the oil change. The vehicle is using 5w-30 Penzoil. Changed by a local shop using a Penzoil oil filter. Fram filters have never touched this vehicle. Odometer reading is 113,000. Oil usage - neglible - not even enough to show on the dipstick. Burns and leaks no oil. No valve noise. Temperature gauge remains midway between cold and the middle and has never gone above that point.
Other vehicles that I've owned since new following the old 3,000 mile range were never as tight as this engine. Either the cars are better now or changing the oil frequently causes wear at startup that builds with each ensuing more frequent change. All vehicles were made by the same manufacturer - Ford. Most of those cars had Fram oil filters. After reading about Fram filters, I'll never use them again.
Reply
mKonkel 8:33PM (8/02/2006)
Penzoil is just a relabeled fram filter look it up.
Reply
APD 5:18AM (8/03/2006)
I drive in the UK and my car's (diesel) engine service interval is 12,000 miles - that's the only time I ever think about changing the oil. My father also drives a diesel engined car which has a 20,000 mile service interval. It amazes me that someone would have to change the oil in an engine as frequently as 3000 miles!
Reply
Eric Bryant 6:14AM (8/03/2006)
"You probably used a coated Hypereutectic piston in the rebuild, right?"
No - it's packing a set of JE/SRP forged pistons.
Reply
MikeW 10:20AM (8/03/2006)
Any makeup oil on the Honda?
Reply
Ben Piller 3:09PM (8/03/2006)
Please name a top quality oil filter brand and why it is considered so.
Reply
Jim D. 6:20PM (8/03/2006)
To #12: One example is a WIX (Napa/Carquest, etc.). It's very good quality due to the quantity and density of the filter media as well as the metal cap rather than cardboard used to maintain filter integrity during operation. A simple test is to simply cut the "can" away to expose the filter. There is no comparison between WIX and Fram. I'm sure there are many other good brands out there also besides WIX.
Reply
David Miller 10:23PM (9/19/2006)
Someone mentioned bypass filters. I've been selling these for 10 years, and if you're looking for documented proof that they work, check out the oil samples on my website: kleenoil.net There is history from a heavy-duty diesel engine (Cat)in a Peterbuilt, with over 700,000 miles, and if you'll notice, he changes oil about every 100,000 miles. He's been using these for 10 years or more. And they're not hard to install.
Reply