Article: How fine is too fine?

[Hohn]

I like this article, because it shoots down a lot of the myths and old wives tales associated with the "hazards" of finer filtration. For engines, the takeaway here is that there's really no such thing as too fine until you are stripping out defoaming silicon particles which tend to be larger and up to 10 microns and potentially filtered out by extremely fine filtration.

Aside from that, there's no downside to going as slow as even 7 microns with very high (beta >1000) efficiency.

https://precisionlubrication.com/articles/how-fine-is-too-fine-in-oil-filtration-systems/

Is Micron Size Alone Enough to Specify a Filter?​

What irks me most is when people talk about filtration and discuss the micron rating without stating the Beta Ratio or Capture Efficiency. The observant amongst you will have noted that my guidance on the filter sizes stated above was with a Beta Ratio (ß) of 1,000 or a Capture Efficiency of 99.9%. This is three times better than a Capture Efficiency of 90% or a ß of 10.

This is a critical point-- one without the other is incomplete and not a sufficient basis for comparison.

 

[Carlostrece]

So based on what the OP said about silicon and defoaming, would that mean 11 microns is the smallest you'd want to go?

The smallest particle rating I'm aware of for oil filters is 20 microns @99.x%. I don't know what the x is.

 

[Patman]

I’ve often wondered what is the best possible filtering we could see from a full flow filter. I know with bypass filters it can be super low but will we ever see a spin on filter at 99.9%/10 microns?
It doesn’t seem like the industry is going that way as there really haven’t been massive improvements in filtration in the last 20 years

 

[JohnnyJohnson]

If it doesn't filter out the ad pack or restrict flow it isn't too fine.

 

[UNC054]

Certain Donaldson filters with the synteq media offer 99% @ 15 micron which is the lowest I’ve come across regarding full flow.

 

[Patman]

Certain Donaldson filters with the synteq media offer 99% @ 15 micron which is the lowest I’ve come across regarding full flow.

But is it really the lowest? Don’t we have other filters that claim 99.5% at 20 microns? (And then that might make it even finer if converted down to 99.0%)

 

[EvoMan]

PG filters are reported to be 99.5@ 20 microns.

G

Post in thread 'Not another Valvoline Restore and Protect thread'

Aug 11, 2025

Love talking filters!

Yes, I’ve called PG several times now and the official PG EX(Extended Life) efficiency range is as follows. This also applies to the 10k filters made by PG for others.(Carquest Premium, Microgard Select etc.)

98.7%@15 microns(absolute)
99.5%@20 microns
99.9%@25 microns

The website has finally been updated for the EX showing 25 as the micron rating. The regular 5k filters are still incorrect and show the EX range like above(15-25).

PG has factories in Vietnam, China, and S. Korea. You will see some slight differences between factories but QC remains fantastic...

• GW.

• 
• 

 

[Carlostrece]

Certain Donaldson filters with the synteq media offer 99% @ 15 micron which is the lowest I’ve come across regarding full flow.

What is the x in that 15 microns @ 99.x% Donaldson filter? We have to know x to know if we should be impressed. We can't compare to other filters until we know the x value of each filter.

 

[ZeeOSix]

What is the x in that 15 microns @ 99.x% Donaldson filter? We have to know x to know if we should be impressed. We can't compare to other filters until we know the x value of each filter.

The old yellow PureOne (before M+H got Purolator) were rated at 99.9% @ 20u. There are some old threads about that.

 

[ZeeOSix]

But is it really the lowest? Don’t we have other filters that claim 99.5% at 20 microns? (And then that might make it even finer if converted down to 99.0%)

The OG Ultra in Ascent's ISO efficiency test was 99.8% @ 15u. Re post 368 in the Ascent testing thread.

 

[ZeeOSix]

So based on what the OP said about silicon and defoaming, would that mean 11 microns is the smallest you'd want to go?

If filtering out addives was a big concern, I'd think it would be a published issue with a bypass filter setup, but doesn't seem to be any info about it from people who sell bypass filters.

 

[EvoMan]

What is the x in that 15 microns @ 99.x% Donaldson filter? We have to know x to know if we should be impressed. We can't compare to other filters until we know the x value of each filter.

Here’s what @Glenda W. found out about the PG filters.

G

Post in thread 'Not another Valvoline Restore and Protect thread'

Aug 11, 2025

Love talking filters!

Yes, I’ve called PG several times now and the official PG EX(Extended Life) efficiency range is as follows. This also applies to the 10k filters made by PG for others.(Carquest Premium, Microgard Select etc.)

98.7%@15 microns(absolute)
99.5%@20 microns
99.9%@25 microns

The website has finally been updated for the EX showing 25 as the micron rating. The regular 5k filters are still incorrect and show the EX range like above(15-25).

PG has factories in Vietnam, China, and S. Korea. You will see some slight differences between factories but QC remains fantastic...

• GW.

• 
• 

 

[kschachn]

If filtering out addives was a big concern, I'd think it would be a published issue with a bypass filter setup, but doesn't seem to be any info about it from people who sell bypass filters.

I think the concern is way overblown to be honest. If you're not filtering out the multi-million molecular weight VII then you're not filtering out the smaller siloxane molecules.

That's just my opinion.

 

[Carlostrece]

If filtering out addives was a big concern, I'd think it would be a published issue with a bypass filter setup, but doesn't seem to be any info about it from people who sell bypass filters.

How fine do bypass filters filter?

 

[ZeeOSix]

How fine do bypass filters filter?

A good bypass filter is typically 98-99% at 2 microns. So if filtering out additives was a big concern, I'd think the companies that design and sell them would be saying something if it was a big concern.

 

[Carlostrece]

A good bypass filter is typically 98-99% at 2 microns. So if filtering out additives was a big concern, I'd think the companies that design and sell them would be saying something if it was a big concern.

What micron rating @ 99.9%?

 

[SubieRubyRoo]

What micron rating @ 99.9%?

Read 2 words further in the post

 

[ZeeOSix]

What micron rating @ 99.9%?

Doesn't matter if it's already capturing 99% of 2 micron particles. If it was stripping out a lot of the oil additives, then I'd think the makers of these super efficiency bypass filters would say something about it.

 

[twX]

Apparently viscosity modifier can also be filtered out with filters that are at least 99% at 10 micron. From the ISO 3968 standard for hydraulic filters:

Caution should be exercised when testing fine filters (β10 > 75) on hydraulic fluids with viscosity index improvers at lower temperatures (<30 °C), as the additives can be temporarily removed and can partially block the element.

It probably only applies to certain types of VM with very long chain polymers. It sounds like they only get filtered temporarily until the oil warms up, with the issue being that it can temporarily restrict the filter element until then.

 

[Carlostrece]

Apparently viscosity modifier can also be filtered out with filters that are at least 99% at 10 micron. From the ISO 3968 standard for hydraulic filters:

Caution should be exercised when testing fine filters (β10 > 75) on hydraulic fluids with viscosity index improvers at lower temperatures (<30 °C), as the additives can be temporarily removed and can partially block the element.

It probably only applies to certain types of VM with very long chain polymers. It sounds like they only get filtered temporarily until the oil warms up, with the issue being that it can temporarily restrict the filter element until then.

Could that cause the filter to go into bypass mode for a while?