Oil filters pass grit

[bbs]

So this was a surprise, but not on an engine but a modified Harbor Freight solvent tank.

I'm rebuilding my transmission and I need very clean solvent. On my solvent tank I added an external automotive oil filter and replaced the pump with good flow but near zero pressure.  I used an STP S5 filter (20 micron), and solvent pumped out left fine material in a white plastic bucket.  Not good for cleaning transmission parts.  I bought a Mobil 1 M1-302A thinking as it was designed for synthetic oil it would filter better, but it left even coarser material in the white plastic bucket. Both filters are tested to 20-30 microns and honestly the vendors don't claim micron ratings, but visible grit is larger than tested.  Maybe the oil filter bypass valves leak and need pressure to seal? 

Since I need cleaner solvent, I used a big blue 10" housing filter I had and bought 5 micron 2.5 x 10 sediment filters from Lowes.  Clogged up in 10 minutes, flow slowed to a trickle.  Replaced the filter, all three are in the photo below.

I also had the pump running for a while to clean the solvent through each filter, stirring up the solvent and the flow never slowed. Seeing the grit in the filtered solvent makes me worry about the oil filters I buy for my engines.   

[Katfish]

Interesting, wonder if a transmission filter would be better or worse.

[dodj]

Ya there has to be a compromise between filtration and flow. I know on the diesel forums I check in on from time to time there are threads about bypass filtering. That's where you use a much better filter, like 5 micron and only filter a portion of the oil flow. Because if you filtered the full flow of the oil to that level the engine would get starved for oil.
Engines put up with a lot of crap in the oil when you think of it....and survive.

[pschlosser]

Most automotive oil filter systems have a bypass for when the filter becomes too clogged.  in those cases, the oil filter doesn't filter at all, more or less.  I think the bypass can engage when starting in cold climates, too, as the oil is more viscous.  but once things warm up, the bypass is off.  I'm wondering if the OP is using a housing with a bypass.

TL;DR filtering to 5 microns may be impractical.  my advice, clean the parts with your parts wash, and disregard the particle sediment.  after cleaning, spray the parts down with a degreaser, and rinse them with high pressure hot water. after rinsing, blow them dry with compress air, and submerse them in clean oil, and allow to drain on a rack.

most auto parts store cartridge filters only filter down to 30 microns, or so.  the particles that get through can also clump and be seen in areas where there is little oil flow to keep them moving.  

I saw this at a print shop, where we had a large parts wash basin filled with digital press imaging oil running through a FRAM automotive filter.  in the far corners of the holding tank, that should only be filtered oil, one could see these clumps and when squeezed between your fingers, would sort of disappear and dissolve into a smudgy dirty oil.  I don't think this can easily occur in our mopar engines, because the bottom of the oil pan, the sump, is small enough that all areas get sucked by the pickup and things stay moving.

back in the late 1980s, a friend put an external oil filter that used a fine screen filtering to 5 microns on the family Mercedes diesel wagon.  the idea was to filter the oil so well, that it removes the carbon particles common to diesel engines, and the idea was the engine oil would not turn black after an oil change.   it was observed after an oil change, the oil to be dark and near black within a few days of driving.  

the external filter housing was like 8-inches square, and about 2-inch thick.  it had an indicator to show when it was clogged enough to be on bypass, and signaling it needed to be cleaned.  it worked!  it kept the oil clean enough it stayed golden brown. 

initially, after it was installed, we had to clean it about 6 times that first day, maybe more in the days after, but I was not following along with the number of times it was cleaned.  we figured there was carbon trapped in places within the engine, so we expected more frequent cleaning at first. one lost some 4 ounces (1/8-quart of oil) with each cleaning, so even the first day, we had to top things up.

but in the end, it proved too impractical. it evolved into a need for cleaning about 2 times per week.  he got sick of cleaning the filter, and just ignored it, allowing the cartridge filters (still in place) to do its filtering.

for an automobile, I'm not sure how practical filtering to 5-10 microns will be, given it won't last the 5000 miles or 90 days (for those you change frequently)