Oil Life Question

[frank1492]

I have a friend who has a Nissan Murano that is driven very sparingly.
Sometimes at the end of a five or six-month period, she has not accumulated
enough miles to reach the oil-change interval, but she will change the
oil anyway.
Logically, it would seem to me that if oil is not circulated
through a running engine, it cannot deteriorate because it's not
building up grit or impurities. But is there any possibility that time
alone can be a factor?
I tell her she's just wasting her money and to always wait until she reaches the interval before changing. What would you say?
Help much appreciated.
Frank

[shorod]

I'm not an oil expert, but I've read that the oil exposure to moisture in the air and being in contact with the metal parts of the engine still cause the addititives to deteriorate, which is one of the reasons they often used to suggest 3 months or 3000 miles. However, I don't remember seeing very many owner's manuals that suggest anything other than the mileage.

So, my suggestion would be to read the owner's manual for the vehicle and, when using the grade of oil specified in the owner's manual, go off of what the manual suggests for the type of driving your friend exposes the vehicle too.

Ultimately though, it would take a lot of oil changes to exceed to expensive of any major engine bearing/crankshaft/camshaft repair though.

-Rod

[curtis73]

She's absolutely right. Oil is kinda like wine. Once its opened, it starts oxydizing. There are a small percentage of volatiles in oil (things that evaporate), and the additives start breaking down. Moisture in oil is not a problem in an engine that is run consistently because the hot oil evaporates the water out, but left to sit the water can mix with some of the additives and become acidic.

Having said that, old oil doesn't mean instant death. Its still oil, and it will still lubricate the same for the most part, but its pH and other chemical properties will reduce its ability to neutralize blowby gasses and soot and other things. Physically it is the same oil after 6 months, but chemically it is not.

I guess if I had an old rusty pickup with a tired V8 in it, I would change it based on mileage, even if I only put 3000 miles on it per year. The $30 cost of a preventative oil change at 1000 miles and 4 months isn't worth it on a $300 pickup... but, on a more high-end vehicle, or for an anal car owner, its $30 of cheap insurance.

[MagicRat]

Good answer.
One more thing........ going strictly by mileage for oil changes is often misleading. Car companies have a tendency to overestimate the mileage that can be driven before a change is required, given many people's driving habits.

You may note on many owners manuals, they indicate different maintenance shedules for 'normal' and 'severe service'. Usually the latter includes more frequent oil changes.

However, they do not indcate or downplay exactly what is meant by 'severe service'. Anyone who regularly drives in urban conditions, colder or extremely hot weather and/or short trips is in the 'severe service' category.

Imo they do this for marketing reasons, fearing they may lose sales or customer's confidence if they recommend frequent oil changes.

Recently. I read that car manuacturers consider virtually all car owners who live in Canada and the northern US fall under into the 'severe service' category. (can't find a reference for that right now). So the oil changes are not a waste at all.

[CL8]

What about a quart of oil thats been sitting in your garage for a year unopened, would that also deteriorate?

I recently found a container of brake fluid, with no lid on it sitting in my garage probably two years old or more, would that be safe to put in my vehicle, or should it be thrown out?

Thanks, Cl8

[curtis73]

Oil has a shelf life (just like wine) but 1 year should be safe. Most oil tested at 3 years still sealed is on the borderline, but a sealed container of oil will last a long time.

Brake fluid is not oil, nor is it petroleum based. Its a glycol-based fluid that is VERY hydrophillic, meaning it is very absorbent of water. If its sealed it will last practically forever, but once opened its only good for a few months, even WITH a cap. If you have some without a cap, I wouldn't use it after a week let alone a year.

[shorod]

Originally Posted by curtis73

Brake fluid is not oil, nor is it petroleum based. Its a glycol-based fluid that is VERY hydrophillic, meaning it is very absorbent of water. If its sealed it will last practically forever, but once opened its only good for a few months, even WITH a cap.

I believe you meant "hygroscopic."

I'll give you another chance to correct/clarify what I type now. As for oil sitting in a sealed bottle on a shelf, part of the reason that does not deteriote as quickly as when sitting in an engine is because it is not in contact with metal and the combustion byproducts mentioned above, plus it is not exposed to the atmosphere which often contains a fair amount of moisture.

-Rod

[MagicRat]

Originally Posted by shorod

I believe you meant "hygroscopic."

Like Curtis, I also have seen the term "hydrophilic" used in technical articles to describe the water-absorption characteristics of brake fluid.

I agree that "hygroscopic" also seems to describe the same characteristics.

But I suspect the two terms are not exactly synonymous and may describe different mechanisms of water absorption.
As I am not a chemist, I do not know which term is more accurate with respect to brake fluid.

[CL8]

Originally Posted by shorod

I believe you meant "hygroscopic."

I'll give you another chance to correct/clarify what I type now. As for oil sitting in a sealed bottle on a shelf, part of the reason that does not deteriote as quickly as when sitting in an engine is because it is not in contact with metal and the combustion byproducts mentioned above, plus it is not exposed to the atmosphere which often contains a fair amount of moisture.

-Rod

So would you agree with Curtis73 that oil sealed in its container is good for 1 to 3 years?

[CL8]

Originally Posted by curtis73

Oil has a shelf life (just like wine) but 1 year should be safe. Most oil tested at 3 years still sealed is on the borderline, but a sealed container of oil will last a long time.

Brake fluid is not oil, nor is it petroleum based. Its a glycol-based fluid that is VERY hydrophillic, meaning it is very absorbent of water. If its sealed it will last practically forever, but once opened its only good for a few months, even WITH a cap.

unless you leave it out in the rain, how can water affect it when the cap is off? (especially in a dry climate such as Arizona)
Or does it deteriorate in other ways as well?

If you have some without a cap, I wouldn't use it after a week let alone a year.

[curtis73]

I don't care if you live in Arizona, New Mexico, or the Serengetti... there is always moisture in the air. I'm sure you've picked up a piece of cloth on a humid day and felt that it was a little damp. Now imagine that times 10. Glycol based fluids (like brake fluid) are very quick to absorb any ambient moisture in the air. The only safe brake fluid is in an unopened, sealed container. Even if you opened a container, used half, then put the cap back on, you have replaced half of the volume of the container with ambient air. The moisture in that air will absorb into the glycol.

Then what happens a month later when you dump that fluid into the master cylinder and bleed it through, you have a fluid with small amounts of water in it. It doesn't matter if you have the tiniest bit of water, what happens is the brakes get screaming hot. The water evaporates and makes a tiny gas bubble. And, as you know, gasses compress, fluids don't. All that time you spent getting air out of the system is ruined by a tiny steam bubble.

And, to clear things up...

Hygroscopic has come to mean the same thing as Hydrophillic. Hygroscopic is not widely accepted as the best definition, since it was a term derived from the instrument used to detect water; the hygroscope. If you translate the latin, hygroscope basically means "looking at water." The word hygroscopic was adopted to mean anything that tested positive using a hygroscope. But, literally translated, hygroscopic is basically an adjective that means "water looked at."

The term hydrophilic comes from the latin roots of "hydro" (water) and "phil" (love of). Such are derived the words; philanthropy (love of humans), the name Phillip (love of horses), philander (love of a man - from the latin andros). In scientific circles, the hydrophilic word is the proper designation for a substance that readily absorbs water.

Put it this way... if you get a positive result for water from a hygroscope and call it hygroscopic, that is like getting a positive result with a metal detector and calling the discovered substance "detectorous." You don't use the machine to describe what you've found.

The proper scientific term is hydrophillic, but since hygroscopic has become so widely used, I accept it as well as I've accepted the phrase "cummings diesel." I don't like it, but everyone uses it, so I have to put up with it

[shorod]

Originally Posted by curtis73

And, to clear things up...

Hygroscopic has come to mean the same thing as Hydrophillic. Hygroscopic is not widely accepted as the best definition, since it was a term derived from the instrument used to detect water; the hygroscope. If you translate the latin, hygroscope basically means "looking at water." The word hygroscopic was adopted to mean anything that tested positive using a hygroscope. But, literally translated, hygroscopic is basically an adjective that means "water looked at."

The term hydrophilic comes from the latin roots of "hydro" (water) and "phil" (love of). Such are derived the words; philanthropy (love of humans), the name Phillip (love of horses), philander (love of a man - from the latin andros). In scientific circles, the hydrophilic word is the proper designation for a substance that readily absorbs water.

Put it this way... if you get a positive result for water from a hygroscope and call it hygroscopic, that is like getting a positive result with a metal detector and calling the discovered substance "detectorous." You don't use the machine to describe what you've found.

The proper scientific term is hydrophillic, but since hygroscopic has become so widely used, I accept it as well as I've accepted the phrase "cummings diesel." I don't like it, but everyone uses it, so I have to put up with it

Once again you've impressed me. I even did a quick Google "define: hydrophillic" before making my post since I had never heard that term, but had heard "hygroscopic." Google "define" yielded no results. Now I see that the word only has one 'l' -> hydrophilic, which Google would have told me if I didn't do such a quick check. So, I'm still impressed with you and with Google.

Once again, this forum has taught me something!

-Rod

[MagicRat]

Originally Posted by curtis73

The only safe brake fluid is in an unopened, sealed container. Even if you opened a container, used half, then put the cap back on, you have replaced half of the volume of the container with ambient air. The moisture in that air will absorb into the glycol.
substance that readily absorbs water.

This is why, whenever I leave a partially-used bottle of brake fluid, I squeeze the plastic bottle until the fluid level is flush with the top of the bottle, then put the cap on. This way, the fluid is left with no trapped air in the container.

[curtis73]

Originally Posted by MagicRat

This is why, whenever I leave a partially-used bottle of brake fluid, I squeeze the plastic bottle until the fluid level is flush with the top of the bottle, then put the cap on. This way, the fluid is left with no trapped air in the container.

Now who's the smart one that's a great idea.

[CL8]

Thanks Curtis73 for the answer about brake fluid and an informative English lesson

Bear with me if you would (I have no formal education in auto mechanics)
But does anything keep the brake fluid from absorbing water once it is in the master cylinder of your vehicle?
The only time I have had to replace brake fluid was in vehicles at the driving school I work for that have had a leak in the brake fluid.
I can't remember any of my personal vehicles that I have had to even open the cap for the brake fluid.

Thanks, Cl8