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Lcubed (Structural) (OP)
18 Jul 05 13:43
Hi All,
Could anyone tell me the direction and (ball park) rate of flow through an automotive oil filter? Thank you.
amorrison (Mechanical)
19 Jul 05 16:14
IRstuff (Aerospace)
19 Jul 05 17:19
Not specifically related, but at least, it gives some values:

Also, in confirmation of previous posts about the direction of flow in the filter:


Lcubed (Structural) (OP)
19 Jul 05 18:38
I think I have what I need. Thanks to you all for the help.
patprimmer (Publican)
19 Jul 05 18:53
It definitely goes from outside to inside. Built in check valves and bypass valves will not work when you try to flow it the other way


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evelrod (Automotive)
20 Jul 05 12:15
Many, if not most, filters have "anti drain back" features that prevent the filter from draining out on shut down.  This little feature makes reverse flow impossible.

   [Pat, guess how I figgured that one out.]

Flow rates are determined by filter size and filter medium.  Larger filter...higher flow (generally)...smaller filtration (partical size) lower flow.  Racing filters tend toward full flow, high flow/low filtration (e.g., Fram HP-1 or Wix 51515R)  whereas "street" filters usually compromise with a small particle filtration capability (as low as 5 microns in some cases) and a "safety bypass" valve in the event flow becomes unduly restricted. This "semi full flow"(my term) is usually ok as long as it is changed often and is NOT used in a high performance application. Street equivelents of the above examples would be Fram PH-8 and Wix 51515.  Big difference in filter flow and capacity.  Like anything else, use of the proper filter in each application is paramount.

Lcubed (Structural) (OP)
21 Jul 05 11:03
How many gallons per minute for the higher filter flow types?
evelrod (Automotive)
21 Jul 05 12:15
Sorry.  I don't have access to that info any longer.  You can Google up  "Oberg",  "Canton/Mecca" or "Canton Racing Products" for oil filter "screens" and filters that flow very high rates (but with only something like 250 micron filtration).
The only "off the top of my head" numbers I have are for Wix and KN racing filters and they are in the 16 gph range as I recall, when new.  I change filters and oil after each race and cut open the filter to check for condition.
IMO, there just is no need for ultra high filtration media in a racing application.  Basically, all you need is to catch "the big chunks" to keep a race engine alive for the few hundred hours it is ever likely to see. I would, however, always use at least a 25 micron screen in the fuel filter, if that's any help.

As to maximum flow rates of oil pumps...all I can say is that I saw some specs on a Hoburn/Eaton I used once that flowed something like 70gph, unrestricted.

Take all this with a grain of salt as I am working from memory.  Check with each mfgr before installation for up to date specs.  Better safe than sorry.

DaveBidner (Automotive)
25 Jul 05 23:12
Hi Lcubed,
Something else to consider, seems to me that the pressure regulator is build into the pump meaning the spill never made it to the screw-on filter and it was a partial flow of the pump. The particular one I last had apart any way.
Dave B
evelrod (Automotive)
26 Jul 05 11:47
Yeah, Dave, the bypass flow generally goes directly  back to the sump and thereby bypassing the filter.  On my UK Ford based engines the pump bypass is blanked off with a core plug and, of course, on the dry sump pumps there is only a small drilling to lube the gear drive on the jack shaft/camshaft. (It's pretty obvious that there is no bypass on externally driven pumps).
Most oil filters have built in bypass valves so if you want a true "full filtration" filter, check the specs. On regular "high filtration" filters, as low as 5 micron but generally around 25, full flow never happens.  Over the average of many miles and hours, it is assumed that all the oil eventually goes through the filter media.   That is not what I need for a race engine, for sure. A high flow/low filtration race type will do it for me.  All I need catch is the "big chunks". It's uncommon for a race engine to see 100 hours of service without a teardown. Indeed, my last one only did 16 hours!!!

patprimmer (Publican)
26 Jul 05 18:39
My interpretation of full flow is that all oil is filtered on its way to the bearings. Any oil bypassed to the sump does not really matter, so I don't take pressure relief valve flow into consideration other than the waste of pumping and heating it.

Bypasses in the filter are only momentary as the pressure equalises after start up, however as the oil that bypasses is in the bottom of the filter and has had time for foreign body settlement, it is a bad thing in my opinion.

In race engines, I block the bypass as I expect the filter and oil will be changed so often, that filter blocking is not a risk.

In road engines I normally run a filter with a built in bypass.


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evelrod (Automotive)
27 Jul 05 11:40
Well, so far, no one has mentioned my error in the post of 21, July---filter flow rate for the Wix and KN racing oil filters should be "gpm" and not "gph".  Sorry.

Pat, some of the filters with built in bypass are set at rather low pressure differential. Often around ten psi in some cases.  That would mean the filter could get bypassed rather often on cold start up, I  would guess.  I have never really checked...maintenance on my street stuff lacks enthusiam and race filters have no bypass. Pressure drop across a Wix 51515R, 19 row Mocal and, ~8' of -010 hose was about 5 psi with 20W50 Castrol @ >200f on the Lotus if my memory is correct (that assumption is ALWAYS suspect).


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