When to change low mileage conventional or synthetic oil, 6 or 12 months

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Jun 22, 2016
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MI
I know the low mileage OCI has opinions all over the place but I don't get why this isn't more agreed upon. After engine oil has been put in an engine and run a few hundred miles does it start to break down faster than oil new in an open bottle? If it does begin to break down faster than unused oil does it break down to the extent to benefit from replacement at 6 or 12 months? I know oil has lasted in the ground for millions of years and in sealed bottles for several years just fine but that doesn't apply to oil that has seen a few hot/cold cycles and been introduced to the combustion environment. I guess I can do an oil analysis at 6 and 12 months myself to see how the additives have aged but I would think someone who reads this forum would have done that already.
 
The challenge is that engine varies from car to car, even cars from the same make/model/year made in the same factory using the same machine.
I know you may think that the machine can create something exactly the same but not so.
Engineers work with tolerances when they design a mechanical system while the machine that manufacture the mechanical system have tolerances too. So, nothing will be exactly the same.

On the oil side, it is also varies from batches of oil made even in the same.
The spec is specified with tolerances NOT absolute.
 
It makes no difference whether you do it at 6 or 12 months.

Look in the manual for their suggestion.

Which one makes you sleep better?
 
I change it at 6 months or 3,000 miles I was doing 3 months but that was wasting oil for the amount I drive. I wouldn’t go past 1 year based on what I’ve read here. So either way would be fine.
 
The OLM on my wife's 2018 Honda CRV went off at 12 months. With her working at home due to covid and the vehicle being driven infrequently, it was the first time I've ever had a car require an oil change due to time rather than mileage.

I wouldn't worry much at all about a car that had been driven a few hundred miles. I'd still change it at 12 months I suppose, but the one I'd be more worried about would be a car that had 4,000 - 5,000 miles on the oil. Presumably you'd have eaten into the TBN appreciably at that point and I'd worry more about that oil sitting in the sump for a longer time than basically new oil with hundreds of miles on it.
 
FYI - some of these short drain intervals hark back to the days before oils had additives to make them somewhat basic. So oil in the bottle was essentially pH neutral and as soon as you put them in the sump and starting driving on them they became more and more acidic.

Now that TBN is a thing and most oils start in the 6 - 8 range you're not going to get into acidic territory until the oil is near the end of it's life.
 
FYI - some of these short drain intervals hark back to the days before oils had additives to make them somewhat basic. So oil in the bottle was essentially pH neutral and as soon as you put them in the sump and starting driving on them they became more and more acidic.

Now that TBN is a thing and most oils start in the 6 - 8 range you're not going to get into acidic territory until the oil is near the end of it's life.
It harks back to those days, does it?
 
After reading this article:
I've had a change of heart. Before reading that, I felt I should change my low mileage vehicles every 6 months, even if there was <3000 miles on the oil. After reading, I'm confident going 12 months. At the rate of my current driving, that means 3-4k miles on my Civic, 5k miles on my Ranger, and 5k miles on my CR-V. In general, I'm pretty comfortable with 6k miles or 12 months, whichever comes first. Read the article and do what feels right for your needs.
 
If you're not hitting the mileage stated by OLM/owners manual and don't want to spend money on a UOA then a year is what is suggested by most. I noticed on the Wix oil filter box it says not to exceed 12 months.
 
I change it at 6 months or 3,000 miles I was doing 3 months but that was wasting oil for the amount I drive. I wouldn’t go past 1 year based on what I’ve read here. So either way would be fine.
And you're still wasting oil.;) I did 3K mile intervals for the first 30K miles then decided to start doing 5K mile intervals on my '97 Ford Escort with 41K miles on it. It's probably been about 3 years since it's last oil change and has only been between 1-2K miles but about 1K miles of that was a road trip from KY to NC and back. I'm also using conventional 10w40.
 
And you're still wasting oil.;) I did 3K mile intervals for the first 30K miles then decided to start doing 5K mile intervals on my '97 Ford Escort with 41K miles on it. It's probably been about 3 years since it's last oil change and has only been between 1-2K miles but about 1K miles of that was a road trip from KY to NC and back. I'm also using conventional 10w40.
You are definitely more brave than I am.
 
I'm on the same conventional oil (10W-30) for 2 years at 2K miles in one of my car. I'll probably change it at around 3-4K. Oil is under a lot more stress while the car is in operation than it is just sitting in the oil pan and engine. The small amount of evaporation or chemical rx is trivial compared to when the oil is in use in cars. Blackstone UOAs have said that oil in cars can't tell time, it's largely dependent on mileage and driving habits.

Have a listen to Blackstone's podcast about this:
 
Correct, oil essentially does nothing while sitting in the pan as it is the products of combustion that cause it to degrade.

The reason an automaker sets a calendar limit is because they do not necessarily know the conditions of operation for the oil. Lots of short-trips in a cold Wisconsin winter is vastly different than long drives in the summer.
 
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You are definitely more brave than I am.
My mom still has the 1999 Grand Marquis that my dad had when he passed away in 2010. She doesn't drive so the majority of the miles it gets now is when I take her places in it or if we're going on a highway trip together. I think I've had the oil changed either 2 or 3 times since dad passed away in 6/2010. It was getting 5K mile OCI's when dad was living and that's what I'm still doing with it. I'm very comfortable with 5K mile intervals as long as it's not mainly short trips. Dad bought a new Mercury Montego in 1968 but had another car that he used as a daily driver. When he took the Mercury for a daily driver in 1974 I think it had about 30K miles on it and had had an oil change every 3K miles although it wasn't continually used for short trip/towing/etc. This was with late '60's and early 70's era oil. When dad sold the Mercury it had 168K miles on it. Sometimes it used a quart between changes and sometimes it didn't. In 1968 Ford's recommended OCI was 6K miles and 3K for severe duty.
 
My mom still has the 1999 Grand Marquis that my dad had when he passed away in 2010. She doesn't drive so the majority of the miles it gets now is when I take her places in it or if we're going on a highway trip together. I think I've had the oil changed either 2 or 3 times since dad passed away in 6/2010. It was getting 5K mile OCI's when dad was living and that's what I'm still doing with it. I'm very comfortable with 5K mile intervals as long as it's not mainly short trips. Dad bought a new Mercury Montego in 1968 but had another car that he used as a daily driver. When he took the Mercury for a daily driver in 1974 I think it had about 30K miles on it and had had an oil change every 3K miles although it wasn't continually used for short trip/towing/etc. This was with late '60's and early 70's era oil. When dad sold the Mercury it had 168K miles on it. Sometimes it used a quart between changes and sometimes it didn't. In 1968 Ford's recommended OCI was 6K miles and 3K for severe duty.
Wow 2 or 3 times in almost 11 years 😳!. I suspect it would start to really break down by then.
 
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