Can someone explain to me how a relief valve works on an oil filter. I was recently cross referencing one brand of oil filter to another brand for a part number when I came across some specs for each filter that didn't match. The relief valve PSI's were different - 9-11 PSI vs. 12-15 PSI. I'm just a guy who likes to know how things work. Thanks.

 

Supposedly when the differential pressure across the filter reaches the claimed value the relief, (or bypass), valve opens. In other words, for the two filters you were looking at, if they started plugging up, the one with the lower setting would bypass the oil sooner.

 

To simplify, if the filter plugs up, the bypass valve will open allowing the engine to get oil. Even dirty oil is better than NO oil.

The way to keep from having to worry about this is to change oil and filter FREQUENTLY rather than leaving it in there so long that it plugs up. If you're changing oil and filter as often as you should, it won't even get close to being so stopped up as to utilize the bypass valve.

Good luck,
Doc

 

I guess technically speaking, as the others have noted, the oil filter has a "bypass valve." The relief valve is at the oil pump and ensures that you don't get too much pressure under high rpms and or too thick of oil (either from wrong grade or cold oil). There has been some talk at the oil guy site that the filter bypass valve pressure setting has more to do with the individual filter than the engine the filter goes on, that is, the bypass protects the filter from damage. You can look at different brands of filter for the same application and get quite a variation in bypass valve pressure settings, which tends to support what I just noted. So bottom line, I would not worry about the bypass setting too much, just that it does have a bypass valve.

As for how it works, well there are two locations, dome end of the filter and threaded end. I prefer the threaded end like my favorite FL1A Motorcraft filter has (you can see the spring just inside the hole). Purolator is a nice filter but the FL1A version has a dome end bypass. I had some sludge in my filter during a cleaning and found it in the dome end, which means it would pass into the engine on bypass with a dome end bypass--not so with the threaded end bypass.

If you go with a dome end, make sure it is a spring version (you will see a raided part in the center) and not a clicker (you will see about 6 small holes in the bottom of the filter), which is a piece of metal that bows out (clicker) under pressure to let bypass. The new Champion brands e-core filter is interesting with its combo antidrainback valve and bypass all in one rubber piece. But I tore one apart and the filter element end caps were not glued on very well at all and would come apart. Your safest bet is Motorcraft, Wix, or NAPA Gold, or others with threaded end bypass.

If you want an oversized FL1A, get the 1.5 inch longer FL299, but not Motorcraft as it is too expensive. Instead get the Purolator L40017, which is the only Purolator I have seen that has the threaded end bypass. You have to special order at Advance Auto and they will have them in a couple days at $6 each. BTW, Purolator makes Motorcraft filters (except for those coming from the factory on new cars are Champion).

Antidrainback valve is a rubber flap to keep the oil in the filter so you get quicker oil flow on cold start.

If you have a Ford 3.0 V6 that specs a FL400 filter you should be able to run the bigger FL1A on it, at least it works for my wife's '92 Aerostar. The gasket is slightly different size, but the mating surface is the same on her 3.0 and my F150 which takes FL1A. The Wix site has gasket dimensions.

Did I forget anything?

 

Thanks for the info. Now if I could just figure out how my wife works . . . . . makes automotive lubrication sound like a piece of cake.

 

There are two times when a man does not understand a woman: before marriage and after marriage!