Here is some info lifted from selected sites on the AC PF35L oil filter:
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25013454 Synthetic Oil Filter
The AC PF-35L heavy-duty spin-on oil filter can replace any PF-25 or PF-35 filter on 1968 up Chevrolet V8 engines. It has a 100% synthetic element that is rated at 12 microns. Its synthetic glass filter media provides finer filtration than conventional cellulose (paper) filters. The individual strands of synthetic glass used in the PF35L are smaller and more consistent in size than cellulose fibers. These glass fibers are supported by a polyester sheet laminated on both sides, and the pleated synthetic filter element is backed by a metal screen. This extremely efficient filter can reduce engine wear by 75% compared to conventional filters without restricting the flow of oil.

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This is the same diameter oil filter as the PF25 (standard 350 ci engine) filter, except it is longer. The standard one filters down to 30 microns, which means any particles 29 microns or smaller will continue to circulate. The PF35L has synthetic filter element which filters down to 12 microns which means 11 microns or smaller is the circulating chunk size. Because the filter is larger, it requires almost an extra 1/2 quart of oil to be added to crankcase. This longer filter fits and aligns flush with oil pan on 305 and 350 cubic inch engines in the the 3rd and 4th generation F-bodies, so there's little risk of having it bottom out on bumps. But BEWARE if you have a 1995 model with an oil cooler housing since GM redesigned the '95 cooler which causes the PF35L to hang slightly below the oil pan thereby taking the risk that it may hit the ground on bumps and dips. No 1996 or later models got a cooler so there should be no problem there.

------------------------------------------- Quote from Hot Rod: > > "FILTER TIP" > > "Chevy's new V8 heavy-duty "race" oil filter (GM 25013454 or AC PF-35L) can replace any PF-25 or PF-35 filter. Its 100-percent synthetic element is rated at 12 microns and is so efficient that engine wear is reduced by 75-percent in comparison to conventional filters-all without restricting oil flow.

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Terry Quinn (tquinn@heartland.bradley.edu) wrote: > The following information is not specific to the PF35L, but I'm hoping that it applies. > A few years ago, we were working with a filter manufacturer that was promoting synthetic (glass fiber) powertrain oil filters. They had extensive data on the difference between that type of filter and a conventional paper filter.Ø While the synthetic filter is rated for smaller particle collection, that is not the only significant advantage. When filters are rated, they frequently do a so-called "multi-pass" test. I don't remember all the particulars, but contaminated oil is circulated through the filter, under constant flow, a number of times, and the amount of particle removal or collection (cannot remember which way it is tested) after a specified number of passes, determines the micron rating. All the dirt is not removed in one pass. This standard steady state test, with a constant flow, does not tell the whole story, however. What this filter company demonstrated was that when a filter is subjected to pressure or flow surges (such as when starting with cold oil, or even as the flow changes), the filter media will flex. Paper media will then tend to release some of the contaminants back into the flow stream, in a process termed "desorption The standard multipass test will not show this to be a problem, but the release of the contaminants was very significant, and negated much of the advantage of the filtration. The glass fiber media was much more resistant to desorption than the paper media. It also took out more of the contamination in the first pass. But was also considerably more expensive. My employer, Caterpillar, then co-developed a filter with a patented spiral wrap strap around the media to prevent flexing and desorption. So, lacking the ability to use a Caterpillar filter (I don't yet have one of our 10.2 liter diesels in my 93 T/A :-), I'm using the PF35Ls with great confidence that they will make a big difference in engine life.

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