Does motor oil break down over time with little mileage or engine hours?

I have a 2010 Silverado with less than 3500 miles and is now a year old. On Star says I need to change the the oil now. Is it really needed? I also have a tractor with low hours and the oil is several years old (same type question).

Yes, the GM oil life monitor puts the various factors in to estimate oil life. I’d follow it. And ‘several years’ is too long for me. Once a year is my maximum time. What does the tractor owners manual say.

It’s not a question of the oil breaking down in 3,500 miles/1 year.
Instead it is a matter of the oil likely being diluted by water vapor (a normal byproduct of combustion), as well as the potential for oil sludging to take place.

The problem with a vehicle that logs only 3,500 miles in 1 year is that–in most cases–those miles are accumulated mostly with short-distance local driving. That type of driving does not allow the engine and the oil to become hot enough to evaporate the water vapor, and the oil becomes diluted over time.

The process of dilution of the oil, coupled with an engine running on a richer than normal mixture when it is not fully warmed-up, can create the perfect storm for the formation of sludge, internal corrosion, and resulting engine damage.

Normally, I don’t trust the automated oil life monitors on cars to tell me when to change the oil, but in this case, I would suggest that you take its notification very seriously. Even if you are skeptical of an oil change being necessary at this point, the reality that you will void the warranty on your engine by failing to change the oil on the recommended schedule should prod you into action.

If you look in your owner’s manual you will see that GM advises an oil change when the monitor specifies and at least once per year. I can’t say how oil in your little used engine deteriorates but once per year is a tolerable expense. If you made only a few long trips to total 3500 miles, your oil might be ok and you could stretch the change interval to two years. The small savings, however, is not worth encountering the possibility of subtracting from the far end of your engine’s lifespan.

No, oil does not break down just by sitting in your crankcase. But you have been given a number of reasons favoring an annual oil change nevertheless. A change may not be totally necessary at this time but it is a sensible precaution.

It’s unanimous. It should be changed.

As others said, the oil itself doesn’t technically “break down”, but there are very good reasons to change it anyway.

I’d change the tractor oil annually too. Engines…and tractors…are expensive. Oil is cheap. Oil is an engine’s lifeblood. Kept fresh it can do a much better job.

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I agree with all of the above.

I used to have a car that I drove about the same 3,500 miles per year as you. I changed its oil once a year, despite the fact that the specified oil change interval, in miles, was 7,500.

I don’t agree that oil should be changed every six months on low mileage vehicles, but I can’t see leaving it unchanged for more than a year. The reasons why have already been listed by others.

My mechanic for our low-mileage classic says the oil should be changed at least every six months any time after the car is driven, since some of the additives added by the manufacturer will probably be less effective after six months once they are exposed to engine operating stresses. Modern oils are quite good and it’s not like the oil is going to suddenly change into mush after six months, but you are stacking the odds in your favor, and an oil change is relatively inexpensive.
Unlike modern oil, modern ethanol-based fuel is worse than it used to be and that may be even more of a problem for cars which are not driven very often.

I drive my car about 4000 miles a year. Driven 2-3 times a week
The Operator’s Manual says change the oil every 6 months or 5000 miles.
So I change it every 6 months.
However, I change the oil filter once a year.
I don’t think water and unburned fuel get trapped in the filter.

Motor Oil seldom if ever “breaks down”…It’s very stable and retains its properties for a long time. What happens to Motor Oil is that it becomes CONTAMINATED with the by-products of combustion…This contamination can lead to sludging and the corrosion of internal engine parts…

While Motor Oil is no longer cheap, it’s still a lot cheaper than rebuilding engines…

"Motor Oil seldom if ever “breaks down”

Oil definitely does break down…Ever see an engine with Sludge in it?? That’s the result of the oil breaking down…NOT Contaminates…

All oil…after time (even synthetic) will break down.

Transmission oil and other gear-box lubricants can perform for YEARS, operating at high temperatures, WITHOUT “breaking down”…They remain serviceable because they are uncontaminated by combustion byproducts…

“Sludge” in crankcases results from water-vapor collecting in oil or from the oil being partially BURNED by collecting in pockets, hot-spots on top of the head with very little oil circulation and temperatures over 350 degrees…You can call that “breakdown” if you like…I call it poor engine design…Failure to change engine oil in a timely manner compounds these problems because the oil becomes so contaminated with combustion products it can no longer hold them in suspension…

"The Story Of Why Engine Oil Becomes Engine Sludge

By Don Fedak

Fresh engine oil is a clear, free-flowing liquid blend of base stock and additives that contains no fuel, water, coolant, dirt, or other contaminants. In engines that have failed prematurely, the oil has very often been transformed into a high viscosity deposit of brown or black goo, commonly referred to as “sludge.”

When regular engine oil changes are neglected, normally free-flowing lubricating oil breaks down, becomes contaminated, ceases to flow, and is transformed into a thick soup of waste products. That’s when serious engine damage is imminent."

This writer feels that “breakdown” and “contaminated” are the same thing. They are not…

Way back, when multi-viscosity motor oil was first being developed, the “viscosity index improver” which transformed 5 weight oil into 10W-30 oil would indeed breakdown in a process called “shear stability” or lack thereof…These problems have been solved long ago and viscosity stability is no longer an issue…

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I took some time to do a search on the subject and discovered that oil compabies recommend a maximum of 5 years as a shelf life for unopened motor oils, including synthetics. I was unfortunately unable to find anything on the reasons. The American Petrolium Institute ( site has standards established, but I was unable to find the one for motor oil shelf life.

In short, it appears that even unopened oil experiences changes over time. While I’d guess the changes had to do with stratification over time due to different specific graties of the oil’s component elements, I was unable to find anything definitive.

“This writer feels that “breakdown” and “contaminated” are the same thing. They are not…”

I didn’t read that…

The writer did make the statement that as the oil breaks down it becomes more contaminated…That’s true…but he never said they are the same.

Want to create sludge…Pour oil into a frying pan…put on stove and turn on high…In about 10 minutes or so you’ll have sludge…no water needed.

With that kind of mileage I would change it every 6 months at the latest. That type of driving can easily contribute to oil sludging.

Caddyman is correct about the cause of oil sludging. Often this is something that worsens progressively due to the crankcase ventilation system.
Car owner does not have PCV system serviced for whatever reason (how many actually do), oil is contaminated more, PCV system clogs even more, oil is contaminated even faster, PCV…yada, yada, yada.

As the VW service people explained to me at a school one time, engine oil (like transmission fluid or power steering fluid) does not break down. The additives in the oil or fluid do break down an contamination (not related to additive breakdown) can occur.
Place a spoon of tap water into a pan of fresh motor oil and allow it to sit for a few weeks to see what happens.

OK…maybe we’re all just saying the same thing, but differently.

Oil DOES break-down…And when it does break-down it produces contaminates that will turn the oil into sludge.

Water or other contaminates in the oil will also turn the oil into sludge.

Today, the plastic bottles they package oil in will break down before the oil inside will…The oil itself is about 10 million years old when you buy it…

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Yea…but that 10 million year old oil is NOT the same as when it’s brought up from the ground…it goes through a lot of processing.

I just posted this in another thread…Back in the 70’s we started seeing a lot of vehicles with sludge problems…Mainly due to Unleaded gas and their higher temps…Some oils handled the higher temps…others didn’t (like quakerstate).

ALL engines, WAY before 1970, had sludging problems if they were neglected…

“Kendal, the 2000 mile motor oil” This was a big step up from the normal 1000 mile service intervals common up until 1950…

Before engines or heads could be rebuilt, they had to soak 24 hours in a big tank of boiling lye…Man, that was NASTY business…