A while back Fleet and Travel updated its maintenance program on newer vehicles and directed that these vehicles should be changed at 7,500 miles regardless of what the vehicle’s oil life meter recommended. This gave many of the drivers pause as extended oil change intervals are unfamiliar to them. There are some that simply felt that 7,500 miles on an oil change is simply too long. Others became uneasy when the vehicle is indicating that an oil change is required thousands of miles before the 7,500 interval specified by Fleet and Travel. The common thought, from those who cared, was that “we are ruining our vehicles” by running such long intervals.
Since the time this change was initiated, I took the opportunity to solicit oil samples from vehicles in the Sioux Falls Area Office and had oil change technicians sample some the oil when it was being changed. The analysis reports attached took about a year to collect and one vehicle was sampled twice. I took the time and spent my own money on the analysis because I have a natural interest and I saw it as an opportunity to learn. Unfortunately, most of the samples I was able to obtain were on 2018-2018 Ram 1500’s. I would have liked to have gotten some samples from some Chevrolets to compare, however I did sample one older Ford F150.
With the understanding that the algorithms used to calculate oil change intervals are quite complicated and generally do a good job predicting the service live of the engine oil, reviewing the analysis reports was, to me, very interesting. In every case above, the vehicle was telling the operator to change oil thousands of miles before the 7,500 mile mark. Knowing that going in, I was expecting to see reports with some very high wear numbers, and very low TBN numbers. Upon review, they look better than I expected, however there are some values in the report that are a bit concerning.
Looking at any given report, there are a few numbers that generally track with vehicle use and the condition of oil. Iron (Fe), Aluminum (Al), and Total Base Number (TBN) are the three values that one can use to determine if the service interval is appropriate. Looking at the reports as a whole, the TBN at the bottom is all better than I would have expected. There is only one report that has it listed as “cautionary”. Looking at the Iron and Aluminum, all of the reports are indicating very high wear metals. None of them are listed as cautionary by the lab, but generally speaking a report above 50 ppm of Iron and above 10 ppm of aluminum is not great. None of these are high enough to condemn the oil, but they are certainly high enough to take notice.
Another takeaway from these reports is that we are certainly pushing the oil far enough to approach the true end of its useful life. It would appear that the algorithm RAM uses to calculate oil change interval has at least *some* reserve, it would appear that we are using up all of that reserve at the 7,500 mark as indicated by the TBN in the low 2.0’s.
Specifically, on the report for CG040, the TBN came back at 1.7 and is listed as “below the recommended limit” and indicates that the oil was probably in service too long. Looking at that report deeper, you will see that the Iron = 133 ppm, and Aluminum = 11 ppm, further indicating that this oil should have been changed sooner. The viscosity on this sample is also indicating that some significant oxidation has occurred and it is outside of the range for a SAE 5w-20 oil. While this has not been flagged by the lab, it has indeed thickened one grade from a 20-weight to a 30-weight. Taken as a whole on this sample one can conclude that the oil was run too long and should have been changed earlier.
Looking at the samples for CG097, you can see some of the same trends starting to develop. The viscosity is nearing the upper limit, the TBN is near the lower limit, and the wear numbers are higher than ideal.
The two samples for CG038 show a varied use in operating conditions. On the second sample the wear numbers look better, and on the first sample the physical properties of the oil look better. Focusing on the second sample, the vehicle saw predominantly short trips to the construction site and as a result, the TBN was lower and the Viscosity was higher. On the first sample, the vehicle saw more road miles per day – which doesn’t deplete oil additives as quickly – even though the Iron was still rather high.
As a comparison, I included the report for CF734. This oil was changed with 5,300 miles on the oil. On this report the wear numbers are still less than ideal, but the oil viscosity is more in the middle of the range. With the TBN above 2.0 and Viscosity being in the middle of the range for a 5w20 oil, this looks to be a good interval for this vehicle’s use.
Looking at all of the reports as a whole, and trying to look at it from a “big picture” perspective, it appears that the 7,500 mile interval on the newer vehicles may not always be appropriate. In some cases, this interval is extending the service life of the oil beyond the oil’s ability to protect the engine components and beyond the oil’s ability to resist thickening and creating internal deposits within the engine. With just this small sample size of 4 vehicles, one of them is showing clear signs of an over-extended oil change interval, and two more are showing tale-tell signs that the oil is at the end of its service life.
In my opinion, at the 7,500 mile oil change interval, we are not guaranteed that our vehicles are being properly maintained. In the more severe cases, a 7,500 mile interval is clearly pushing the oil in service too long. The manufactures of these vehicles spent a lot of time, effort, and money to develop algorithms which can accurately predict the need for an oil change based on the vehicle’s use. Using the onboard oil life meters on the vehicles equipped with an “intelligent” oil life meter would do a much better job of protecting the investment we made in our fleet vehicles. Vehicles without an “intelligent” oil life meter (older vehicles and many HD pickups) would need a different service plan, of course. Based on a sample size of one (CF734) there is some indication that a 5,000 mile interval may be appropriate.