OIL FILTER BYPASS --EGG ON MY FACE -- Correcting the Record!
 

PROOF POSITIVE: I'm Never too old to learn. At the young age of 72 1/2 yrs, I have always LOUDLY debunked the theory that any Oil Filter would allow (or be designed to allow) unfiltered oil to 'bypass' the filter element and enter galleries unfiltered and thus there was no way junk or sludge could get into galleries. Although, others have occasionally CHALLENGED me on the issue.

Most recently - I posted this erroneous / misleading / uneducated "opinion" in this post.

https://www.f150forum.com/f4/sludge-...2/#post6113629 . No-one 'Blasted' me over it. Such 'opinion based' misinformation occurs all too frequently on forums and largely goes uncorrected. I wish mine had text in disappearing ink - BUT IT DON'T. so I will be editing the above post soon as I post this.

I recently saw a post by my highly respected fellow member @redfishtd (another old fart like me) that caught my attention.
https://www.ford-trucks.com/forums/1...l#post18518330 . I was about to blast HIM, when, as I often do - and should always -, I did a little research on the subject hoping to include some reference material or additional smarts. With sources more reliable than 'YouTube' videos or other Forum Posts, I soon begin to wise up. It FORCED ME TO THINK ABOUT OIL "FLOW" -as it relates to "PRESSURE" and something seldom mentioned - "DELTA PRESSURE".

I LEARNED:
OIL FILTERS ARE IN FACT DESIGNED WITH A BYPASS MECHANISM (or Bypass Valve) to bypass on 'delta pressure' across the filter element! Although their still seems to be some misconceptions about the bypass PURPOSE and numerous VERY important effects that "FLOW RATE" has on a hydraulic system --- (such as which weight oil we should use). ///NOTE: Thicker weight oil - especially cold - IS proportionately more likely to force Oil Filter into bypass///

The OIL filter bypass is not primarily to prevent the filter case from swelling or bursting as freequently suggested. That is controlled by the Oil Pump bypass setting. Two failures would be required to swell a filter housing. a.) Clogged filter or galleys -AND- b.) failed oil pump bypass. Physics of hydraullics dictates that (without 'FLOW') pressure throughout the system is constant from the Oil pump bypass to Chain Tensioners. With FLOW, pressure will drop across each restriction to that flow (ie: delta pressure @ restriction). Hence, restrictors in the heads are sized specifically to provide correct flow (and thus pressure) with 0-20W on new engine surfaces. Restrictors in the heads insures higher pressure is maintained for lower end bearing surfaces while providing proper oil flow for drain back to cool heads, oil lash adjusters - rollers - phasers - timing chains, leaving adequate pressure to operate chain tensioners.

That 'FLOW' should typically be below what would cause restriction (thus delta pressure drop) aross the filter media to force the oil filter into bypass condition. Increased FLOW (High volume pump) increases delta pressure across each restriction. Basically - the filter bypass "SHOULD" never have to be employed unless the filter media is allowed to become overly dirty / clogged, or Oil flow is increased too much by HV Oil pump, or we use OIL too thick to pass through the stock filter media, or run engine RPM too high before EOT comes up to proper range. BUT many factors get involved - and under certin conditions an OIL FILTER can bypass unfiltered oil into the engine.

I guess it is better for it to OPEN and provide 'some oil' to the engine - even if it risks putting unfiltered debris into the galleys.

Hope this helps clear certain things up for anyone as misinformed as I was.

It's rare that people openly say why they were "wrong" and provide proof. I think that is more respectable than knowingly defending wrong information, or saying "I've been doing this for xxxx years, I know what I'm talking about".

So thanks for that.

More great information. I'd known about oil filter bypasses in my other vehicles, but coming from a world of old GMs and Germans, figured the Motorcraft filters had a different design, because Ford. Glad to see that unfiltered oil is still better than no oil (in an emergency)!

Raises awareness of other stuff I don't know that makes me question other decisions I've made. I used the Melling 10340 --- even though couldn't get a direct answer from factory whether it prouced more volume - or just had a stronger spring in the oil pump bypass valve. It prouduces 90 lbs pressure at cold idle (with 5w30 oil). Idles 24 to 27 full EOT temp (after a 30 mile trip). B U T. Now, I also find the oil filter sandwich adapter ports (where my pressure gauge is connected) are in the oil filter 'INPUT' side. !!!! That is reaing oil pressure output from the oil pump ---- NOT the filtered galley pressure like it would be if connecte at the oil pressure sensor location.

SO. While galley pressure does not tell anything about pressure in the heads (at phasers / tensioners), my setup doesn't even tell me what oil pressure is in lower end galleys. (depends on pressure drop across filter element)

We need THREE (3) Pressure gauges tapped in at three places. One at sandwitch adapter. One at oil pressure sending unit port. (Difference = delta pressure across filter element - max would tell you it is in bypass), and One in head galley for phaser / tensioner pressures.

An they say knowledge is 'power'. My '04 runs beautifully and VVT works perfectly (per Torque Pro monitor) 30k miles post timing job. But - Just more questions and stuff I have to be careful not to post too assertively.

Not questioning what FORD uses ... but I live in the industrial filtration world, and bypass valves in cartridge style definitely exist. They are not common, however; bypass valving is usually in the "housing", whether cartridge or spin-on.

F150Torqued, an industrial worry is that a clogged element might collapse with media getting into the system.

Thanks @gbynum Lot of it makes sense. Fascinating how strong opinions about subjects (both right and myth) originate and how hard it is to shake them.

As a young kid (60 + years ago) I lived on a Texas planes farm in irrigation country. The irrigation wells (pumping a 12" columns of water back then) were powered by big block V8s with pretty much deafening straight pipes. They were equipped with twin filter systems with valves to allow changing filters hot -without shutting them down-, and a sight gauge for live oil level. They would sit there running 2700 to 3300 rpms, 24/7 during the irrigating season. I recall seeing the exhaust manifolds 'glow cherry red' at night from the punishing load. I well remember my father changing filters often, insisting that if they clogged up - with west Texas dust (which gets EVERYWHERE) - the engine would be starved of oil and destroy itself. (OR if the Oil Pressure caused a shutdown while unattended, with the transfer case engaged, the 12" column of water rushing back down the well would spin the engine backwards and disintegrate it. What ole daddy believes is gospel truth - right. But I have seen those ole engines run season after season without rebuild - literally multiple millions of miles if on the road at hwy speed. Wouldn't have believed ANY unfiltered oil could EVER get into the oil galleys.

He was close; it'd be starved of filtered oil, and destroy itself. The bypass on my Olds 350 is in the filter adapter, same as my '84 GMC, and my BMW has the bypass build into the filter housing (has cartridge filter). This was done as a failsafe because dirty oil is still better than no oil.