I'm no automotive engineer either, but I take pride in my common sense.

Could the manufacturer's spec of the bypass opening at 12-15psi simply refer to the difference (delta?) between the flow coming into and exiting the filter? For instance, if you have 60 psi coming in and 58 psi exiting, the difference is two, and no bypass results. Meaning, the filter wouldn't bypass at 60 psi unless the pressure drop was more than 12 psi (48 psi exiting).

I expect the pressure relief valve rarely opens in any filter, on any engine, other than when clogged. Bypassing is a last ditch effort to prevent a total engine failure, as in, it is better to have contaminated oil flowing through the engine, vs none or not enough!

 

I very much like this explanation of how it might work. But it would have to work with an oil pressure relief valve somewhere in the system. Otherwise, it might be possible for the oil pump, as a positive displacement device, to put out too much pressure. Is there such a release in the pump housing - I haven't a clue.

 

Lexus Champion is right. Operating oil pressure doesn't mean squat. The relief valve only comes into play when the difference between input and output pressure exceeds the bypass valve setting. The valve opens and allows unfiltered oil to continue to circulate. That is the reason a larger capacity filter is a good idea. Just to stir up things, a filter filters the least when it is brand new and filters the best the instant before the by-pass opens. The smaller the filter pores the quicker it will plug up. As the filter filters the pores get clogged. The more it filters the better it filters. If there was no by-pass valve the filtration would be best when the filter is totally clogged, no flow means 100% filtration, nothing is coming through. Electro-mechanical engineer.

 

Seems pretty much unanimous. We are all learning something new here.
The university of u tub just explains how the relief valve works on videos I have found. Not "when" it works.
Differential pressure across the filter element is the key of course. And contaminated filters can increase filtration efficiency which will increase differential pressure over time. The typical 20 micron filter actually allows a lot of harmful contaminants even when operating as designed. And will ONLY work at that peak efficiency for a relatively short period of time.

That about covers it so far?

Paul

 

I would assume so, although, luckily, I have yet to go that deep into a Toyota/Lexus engine. I rebuilt a number of other engines in the past and all had pressure relief valves in close proximity to the output of the pump. I believe it is a necessary component to prevent blowing seals and such, or, damaging the pump itself.

 

Well, without actually becoming an expert on oil filters, I accept the fact that the relief valve is there, and with the larger FRAM XG3600 filter media, the valve will open much less. 😁 Alls' good. Unless someone has a filter that fits our ride with even more filter area 😏 and full synthetic compatible.

Paul