Oil Life Question

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

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

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.

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.

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

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.

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

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. :confused:

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?

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.

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 :D

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 :D

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

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. :smile:

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. :smile:

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

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

I'll chime in again. While there is a seal on the master cylinder cap, the fluid can still absorb moisture. I'm a believer (now) in flushing the brake fluid regularly. Like most people, I had never changed the brake fluid in my Stealth twin turbo. I took the car to a local track to see which had more guts, me or my car. After a couple of laps to get familiar with the track, I started to push the car a bit. I got to the end of the straight, going around 130 mph, then stabbed the brakes to make the 90 degree turn, there was virtually nothing there brake wise. I mowed a little bit of the grass and putzed back to the pits.

The moisture in my brake fluid turned to steam which easily compresses, causing poor braking. After the car sat for a few hours, the brakes were back to normal and I was able to drive home. During the 4.5 hour drive I had no issues. Under normal driving, no issues. But, after that one experience, I now flush the brake systems in my cars as soon as the fluid starts to noticeably change colors. I also make sure to activate the ABS to get fresh fluid in the ABS pump so the moisture won't corrode the valves, etc. in the expensive ABS pump.

I've since had the Stealth back at the track and never experienced brake fade again.

BTW, the car had more guts than I do, especially with sticky tires installed.

-Rod

I'll chime in again. While there is a seal on the master cylinder cap, the fluid can still absorb moisture. I'm a believer (now) in flushing the brake fluid regularly. Like most people, I had never changed the brake fluid in my Stealth twin turbo. I took the car to a local track to see which had more guts, me or my car. After a couple of laps to get familiar with the track, I started to push the car a bit. I got to the end of the straight, going around 130 mph, then stabbed the brakes to make the 90 degree turn, there was virtually nothing there brake wise. I mowed a little bit of the grass and putzed back to the pits.

The moisture in my brake fluid turned to steam which easily compresses, causing poor braking. After the car sat for a few hours, the brakes were back to normal and I was able to drive home. During the 4.5 hour drive I had no issues. Under normal driving, no issues. But, after that one experience, I now flush the brake systems in my cars as soon as the fluid starts to noticeably change colors. I also make sure to activate the ABS to get fresh fluid in the ABS pump so the moisture won't corrode the valves, etc. in the expensive ABS pump.

That's a good point. As you say, periodic changing brake fluid is necessary but is ignored by most people, (imo) partly because very few manufacturers place it in maintenance schedules.

Face it, there are many people who think that regular oil changes are a mechanics scam to make money. :headshake . Convincing these people that they should spend money to flush brake fluid when no manufacturer suggests it would never fly.

In the classic car world (aka old crocks) most owners change brake fluid regularly or put in DOT 5 fluid, which is silicone based and does not absorb moisture.
(But I read that it is more viscous than regular fluid and does not work as well in some systems)

Agreed. Every other brake pad change I flush the brake fluid. Most of the "wet" fluid is in the master cylinder, so its away from where heat can cause boiling and loss of braking, but water in the master cylinder can cause rust where you don't want it.

The hydrophillic nature of glycol fluids was the main reason behind developing DOT 5 silicone brake fluid. The problem is, silicone fluid requires specific brake parts that won't get eaten by the fluid.

Glycol is cheap, and its not that tough to replace. :)

Brake fluids are hydrophillic by design.
If they weren't, then any moisture which got in the system would sit at the lowest piont (your brake calipers, which are also the hottest point) and would boil at around 100 degrees C.

But hydrophillic brake fluids can absorb some moisture and keep a boiling point well above the boiling point of water.
Brake fluids are rated with two boiling points. Dry and Wet.
Dry is devoid of moisture (like when you first open that brand new bottle), wet is fully saturated but still holding all the moisture in suspension.

As the others have mentioned, keeping your brake fluid fresh and dryest is the best way to keep the boiling point up so they don't boil and fade.

As for engine oil. If you really want to know, then pay to get your oil sampled at the recommended change interval. This will let you know exactly how the additives in the oil are holding up.
It'll cost a similar amount to an oil change, but it has the potential to save you many un-necessary oil changes.

FWIW, I never change my vehicles oil at 5000km (3,000miles). Two of them get oil changes at 10,000km, the other 20,000km.
The militarys that use the same engine as my 4wd change the oil at 16,000km (if the military doesn't count for severe use then who does?), I change it at 10,000km as it's easier to remember.
The shopping basket's recommended interval is somewhere around 14-17000km (can't remember, not looking it up right now), 10,000km is easier to remember and I'm making up for an unknown service history.
My work car is recommended 20,000km intervals.

Thanks guys for the replies.

I'll chime in again. While there is a seal on the master cylinder cap, the fluid can still absorb moisture
Now I was taught, through driver instructor education, that, that seal on the brake fluid cap was to keep DIRT out, not moisture out. I guess I was taught wrong, or is keeping dirt out a factor too?

Anyone have any suggestion on how often the brake fluid should be replaced?
(Maybe we need to start a separate thread about brake fluid.):rolleyes:

I wouldn't say you were taught wrong. I didn't specify what the seal was for, but implied it wasn't for moisture. That just happened by coincidence though and you kindly left me an "out." ;)

The old rule of thumb used to be the brake system should be flushed and new fluid installed yearly. I doubt that frequency applies when DOT 5 fluid is used, and the materials used today may be sufficiently better to increase that interval.

-Rod

This discussion sort of morphed into a brake fluid convo, but from what I know, not all master cylinder caps are airtight. Some will allow air through a small valve or cap to equalize the air pressure as the fluid is drawn into the system from brake pad/shoe wear and operation. Because of this, fresh water-laden air does come into contact with the fluid regularly.

I've also had some MC caps that are truly airtight...as the fluid is drawn down, the rubber seal inside the lid has those nubs that extend down to fill the void. I recall these being better, though messier when you remove them.

I've also had some MC caps that are truly airtight...as the fluid is drawn down, the rubber seal inside the lid has those nubs that extend down to fill the void. I recall these being better, though messier when you remove them.

Another example of an "airtight" system. The hayes brakes I use on my mountainbikes have a completely sealed bladder as the reservoir on the master cylinder.
As well as keeping the fluid away from the atmosphere, it means you can turn the bike upside down without worrying about fluid spills or air entering the system.

Another example of an "airtight" system. The hayes brakes I use on my mountainbikes have a completely sealed bladder as the reservoir on the master cylinder.
As well as keeping the fluid away from the atmosphere, it means you can turn the bike upside down without worrying about fluid spills or air entering the system.

Are you an Evil knevil type that does tricks like that while riding your bike?:smile:

(Did he ever do flips in the air with his bike?)

Are you an Evil knevil type that does tricks like that while riding your bike?:smile:

(Did he ever do flips in the air with his bike?)

Yes, but never intentionally.:smokin: