Here is an exchange I had with Lake Speed and Blackstone Laboratories regarding time versus mileage as it relates to oil change intervals. I'm assuming these answers apply to all automotive lubricants. No one else needs to make the same assumptions though.
My question to Blackstone:
I have read several of your reports stating that the length of time oil sits in the engine has very little impact on its effectiveness and service life. Instead, miles driven (engine operating hours) seem to be the more important consideration.
Is this accurate, or have I misunderstood? If it is accurate, is there an article, blog post, video, or other resource you could refer me to that explains this in more detail?
Blackstone’s response:
Great question.
You are correct. In modern automotive engines, calendar time does not have a significant impact on wear metals found in oil analysis. This is largely due to modern emissions systems, which keep engines sealed and prevent moisture accumulation. In older engines (particularly those from the 1970s and earlier) with open breathers, atmospheric air could enter the engine, allowing humidity and condensation to cause internal corrosion.
We still observe corrosion related to calendar time in engines with open breathers—primarily aircraft engines—so time remains a factor in those applications. When corrosion occurs, it typically appears as elevated aluminum and iron in the analysis.
There are many examples of newer vehicles running oil for several years with little change in wear, which is why we do not place heavy emphasis on calendar time. That said, if the manufacturer specifies oil changes at certain time intervals, it is wise to follow those guidelines—particularly while the vehicle is under warranty. The manufacturer would be responsible for any warranty claims, so staying within their parameters is advisable.
Based on our data and experience, however, using mileage alone as a measure for oil changes generally does not present an issue.
We checked to see if we have published any articles or media on this topic, but it appears we have not. That is not because we are unwilling to share this information—we provide the same explanation to anyone who asks—but likely because of the warranty considerations mentioned above. We would not want to recommend relying solely on mileage, only to have a warranty claim denied because the oil remained in service longer than the manufacturer’s time-based recommendation.
Once warranty coverage is no longer a concern, you likely have flexibility to experiment. Assuming the engine is mechanically sound and the oil is not contaminated, I would be surprised if leaving oil in service for longer than a year caused an issue.
Thank you for contacting Blackstone.
Lake Speed’s response:
Thanks for the email and the question. I concur with Blackstone’s opinion on this matter.
Thanks,
Lake Speed Jr.
STLE Certified Lubrication Specialist & Oil Analyst
SPEEDiagnostix
