Something my mechanic said. True or False???

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My friendly neighbourhood mechanic has a theory that I wonder if it is true. He believes that when the oil is changed and the filter is NOT changed the new oil pushes contaminants out of the old filter. Essentially causing excess wear.

Your thought BITOGers.
 
False. The only problem I see w/ reusing a filter is it getting clogged.
 
While the mechanic may be wrong on this 95% of the time, I think it would be possible for this to happen IF

1. The OCI was WAY too long and the oil had time to break down and form gooey sludge that then was caught by
2. mediocre filter (sub-PureOne grade)which was left installed when
3. new oil with fresh additives was put in, which broke down some sludge and allowed the fine contaminants trapped in it to pass through the filter
 
The only thing new oil would push out of a dirty oil filter is the dirty oil that's in the dirty oil filter.

Why folks don't change their filter when they change their oil is beyond me.
 
If the filter media becomes restricted and the system to go into relief and will wash some of the particals back into the system from the dirty side of the media.
 
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Originally Posted By: Johnny

Why folks don't change their filter when they change their oil is beyond me.


Me too! People outsmart themselves, IMHO.
 
Originally Posted By: rshaw125
Why would you ever change your oil and not the filter???


If you were me and you installed an oversized synthetic filter (check out my FleetGuard LF3554, baby), you may not need to change the filter every OCI.
 
Originally Posted By: Johnny
The only thing new oil would push out of a dirty oil filter is the dirty oil that's in the dirty oil filter.

Why folks don't change their filter when they change their oil is beyond me.


We've seen wear numbers decrease in UOA's on the second use of a filter.
 
No doubt your synthetic filter media in your Fleetguard does an excellent job of filtering. However, your oversized filter just has more dirty oil in it than the regular size filter does.

Change the oil and filter at the same time for the best protection. Filters are the cheapest part of the oil change.
 
Originally Posted By: chevrofreak
Originally Posted By: Johnny
The only thing new oil would push out of a dirty oil filter is the dirty oil that's in the dirty oil filter.

Why folks don't change their filter when they change their oil is beyond me.


We've seen wear numbers decrease in UOA's on the second use of a filter.


...which is due to "caking" that occurs as the filter pores start to fill up. With a premium, high-capacity filter, this can result in a very loooooooooong filtration "sweet spot" where efficiency is very good.

K
 
Well, I almost always change the filter anyway. I just can't stand the idea that "some" oil, a half-quart or maybe a quart stays behind and doesn't get changed when you change the oil.

I'm far from a tribologist, so you might shoot my reasoning full of holes. I am an engineer...

If your OCI is 5K, then if you change the filter only every other time, some significant amount of your oil will be in there for 10K. Would not that portion of the oil, those oil molucules, be more apt to break down, to form acids or sludge?

For me, particles are not the issue. If you're going to change the oil, why not change ALL of the oil (as much as is possible)?
 
Originally Posted By: Johnny
Why folks don't change their filter when they change their oil is beyond me.


When you change your oil with a fluid extractor (Mityvac in my case), and the filter is at the bottom of the engine, it allows yourself to get dirty only every other time.
Since it is in the manufacturer recommendation to change the oil filter every other time, I take advantage of it and stay clean.
 
Originally Posted By: Johnny
No doubt your synthetic filter media in your Fleetguard does an excellent job of filtering. However, your oversized filter just has more dirty oil in it than the regular size filter does.

Change the oil and filter at the same time for the best protection. Filters are the cheapest part of the oil change.


There is so much more to this, beyond the quantity of "dirty" oil contained by the filter can.

1. Oil stored upstream of the filter media must be filtered before it can reach the engine
2. Oil stored downstream of the filter media has been filtered already
3. The recontamination caused by reusing a high-quality filter I am sure is less than that caused by sediment and residue left in oiling passages and the disturbed oil pan.
4. Filters always work worst the very first time they are used. They have to settle in, and in the case of cellulose-based filters, they must settle AND stiffen/harden. Flexibility and shifting of the media allows particles to pass through
5. Cellulose media has many irregularities that become filled with particles, which can actually lead to a better Beta ratio over time because a smaller number of "medium" to "large" particles can pass through with smaller particles lodged in the media "in the way". The reverse mechanism also occurs, where large particles become lodged in the media and prevent passage of smaller particles. This is referred to as "caking".
6. Thus, an undisturbed, used filter with remaining capacity and acceptable pressure drop is better prepared to filter well on the next startup as compared to the same filter brand new.

K
 
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The filter doesn't know the oil is new, so it will work exactly the same. However the dirty oil in the filter will mix with the fresh clean oil. Something I would rather avoid, so I change my filter when I change my oil. Some people feel a used filter is better than a new filter. My feeling is if there is any benefit it is negated with dirty oil mixing into the new oil. JMO
 
Originally Posted By: Kaboomba
Originally Posted By: Johnny
No doubt your synthetic filter media in your Fleetguard does an excellent job of filtering. However, your oversized filter just has more dirty oil in it than the regular size filter does.

Change the oil and filter at the same time for the best protection. Filters are the cheapest part of the oil change.

6. Thus, an undisturbed, used filter with remaining capacity and acceptable pressure drop is better prepared to filter well on the next startup as compared to the same filter brand new.

K

AND it will be a while before the new filter "catches up" to the old one

AND you should avoid opening any hydraulic or lubricating system if at all possible. Learn to use the oil pressure gage to tell you when to add oil.
 
What since does it make to add 4 qts. of clean oil to 1 qt of dirty oil. Don't do it. Change all the oil and a new filter. This is oil change 101.
 
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