Originally Posted By: lockguy
So when a filter says 98% multipass efficiency for 15 micron size particle for instance, is it getting that from the start or is that after some of the "cake" build up?
Also, I was looking on the Purolator website awhile back, they recommend 3k change intervals on one of their filters, I believe the classic. Is that a marketing thing to get us to buy more or is there some science to it? Even a bosch distance plus is only recommended to 10k I think.
I honestly thought somewhere between 5-7k was a good interval for a filter, maybe even pushing it a little considering some recommendations.
I put both of my work vehicles through [censored] and back running 5-7k intervals with oil and filter being changed every time. I just cant see a reason to push it to 10k plus. Still seems unnecessary regardless of efficiency when the filters are so cheap.
Unless your engines have a lot of contamination input, i.e. inefficient or defective air filtration/PVC systems, a lot of soot generation, or oxidation residue (sludge) generation (short hopper), the average fitler is nowhere near full at the end of an OCi. Even a long one. In researching for this:
Oil Filters I asked about how much the average filter was loaded at the end of an average OCI. Nobody could cite a particular study on that but these guys had seen a lot of fitlers so thereir educated guesses have some value. When I asked for an educated guess, I got either "under 50%" or "around 50%."
So far my own tests are bearing this out, as the P1 I am running, which has 12K miles so far, is still showing very low differential pressure. WIth oil at ~180F, it's showing 3-4 psi DP, which is under 50% of the listed bypass pressure of that filter. I have a growing stack of new filters that I will be testing for DP on this truck in a few months so I'll soon find out what various new filters looks like for starting DP.
Your question about efficiency: The rating is taken at the end of the test, when the filter reaches it's maximum differential pressure, but oil filters are not like air filters in that they don't change efficiency as much between the the first and last part of the test. They also don't take in as much junk as an air filter, nor as big a size of junk and don't really build up a "cake." The pores in the media do fill up and that aids filtration somewhat but when I asked the various oil filter people I have interviewed more or less your same question, they say an initial test is not commonly/routinely done but they have done it just to see and there may only be a percent or so difference between the efficiency with a new filter and one that is at the end of it's life.
To run an oil filter efficiency test you have to inject a certain amount of test dust (they use the same fine-grade test dust as is used for air filters) to be able to measure and count the particles before and after the filter. As with air filters, they just stop the test at some early point (measured by flow resistance and differential pressure) but the filter has been loaded to some degree.
A good wearing engine is a product of it's design and the lubricant. Modern engines, especially those with roller cams and no timing chains, once broken in, generate very little in the way of wear metals. An average oil filter can hold 16-18 grams of material before it reaches a high enough differential pressure that it begins to bypass often. If 18 grams of metal, about 6/10s of an ounce, came various parts in your engine over a normal OCI, you'd have other things to worry about besides whether your oil filter was full.
Much, most of what a filter catches is other stuff... dust that gets in through the intake somehow, carbon or soot, and oxidation residue. If you eliminate/minimize what comes in thru the intake, and eliminate the oxidation residue part by using a good oil and having a good driving routine, all you have left are combustion byproducts like carbon and soot (in a diesel). These can be minimized as well and the efficient combustion of a modern EFI engine does that... especially if the owner uses good fuel that leaves few deposits or ash. So when you get right down to it, there is very little for the oil filter to do with a modern EFI... if the outside inputs are low... and that's why oil filters can last a long time.
I have asked for an average engine contaminant generation rate from various industry people and they don't have one. If it's ever been tested, it would be specific to one engine in a particular situation. The only answer I get is "low" with the caveat that "low" only applies to engines with efficient air filtration systems. Almost everyone agrees that an efficient air filtration system is the most important part of controlling contamination inputs. Anything that comes into the combustion chamber is going to get into the oil. Those particles will cause wear, which creates more particles and an endless chain of wear is begun. In many ways, the air filter is the most important part of having clean oil, low wear and long life. An efficient oil filter comes into play more when there are high contamination rates from outside sources...such as from an inefficient or defective air filtration system.
On top of that some oil filters have higher than average capacity. As I said, from the specs I've gathered, the average sized oil filter can hold 16-18 grams. Some premium (syn) filters can hold around 30 grams before nearing their bypass limit.
As to FCI recommendations, most of them are based on a CYA. They want the engine manufacturer to take responsibility for that. If you see a 3K interval, there is usually a caveat nearby that says "or according to the OEM recommendation." A "worst case" situation is envisioned and then it's given a safety factor (in industry typically X2 or X3) and there you have it... CYA.