Oil Filter and Oil Pressure


IHC in the early to mid-fifties.

Golden Jubilee
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Post Mon Jun 17, 2019 7:54 am

Oil Filter and Oil Pressure

I'm wanting to know how much my bypass oil filter on my SD220 figures in to overall engine oil pressure.
56 S120 4x4,
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Golden Jubilee
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Post Mon Jun 17, 2019 9:51 am

Re: Oil Filter and Oil Pressure

Mike,
A bypass filter should have little to no effect on oil pressure unless it is plugged, since it only filters oil that goes back to the oil pan when the oil pressure relief valve opens. The oil pump supplies the oil gallery with increasing amounts of oil as engine speed increases, which causes pressure to increase. At some preset point, the relief valve begins to open, sending oil to the filter, and in turn back to the pan.

Dean
Lifelong Kansan
Grew up with red paint
Moved off the farm 28 years ago.

Golden Jubilee
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Post Mon Jun 17, 2019 2:14 pm

Re: Oil Filter and Oil Pressure

Dean,

Thanks, its been some time since I've dealt with that type of system and I'm sketchy on the details. The relief valve you are referring to is the one built into the canister base correct? I have two filters but unfortunately the one with the easy to access relief valve is damaged. The one I have on my truck now has a relief valve but it is not easy to service.

I bring all this up because when cold I get 35-40 psi at idle and hot those same numbers at speed under load but my hot (normal operating temperature) is about 10 PSI at idle. Not a bad reading but I'd be happier with 15 psi. I have had stovebolt six's in the past that worked well and were reliable at 5-7 psi idle.
56 S120 4x4,

Golden Jubilee
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Post Mon Jun 17, 2019 2:30 pm

Re: Oil Filter and Oil Pressure

A bypass filtering system is not the same as a bypass in a filter or at the oil pump. The bypass system on your engine gets a metered amount of oil through a flow restrictor . The bypass oil in reduced quantities goes through the filter and unrestricted to the oil pan. If the oil pump is working as it should, the small amount of bypass oil should not have any affect on the system main pressure.
Knowing this, any oil filter will work. This will include a modern spin on system. An OEM system will require a n OEM filter.
Pumps move oil in volume. Restriction to flow makes pressure.
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Golden Jubilee
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Post Mon Jun 17, 2019 2:41 pm

Re: Oil Filter and Oil Pressure

Yeah, it is just a fix size orifice in the filter housing, If you have trouble with hot oil pressure suspect bearings not the filter. The orifice is open at all times regardless of system pressure, it is just another path for the oil to flow to the pan.
With oil flow is more important than pressure. As long as you have some pressure at idle I wouldn't worry about it. Two Stroke Detroit's had a low oil pressure switch set a 1-3 psi!.
If you hot oil pressure at speed is less than 10 PSI per 1000 RPM (I.E. 20 psi at 2000, 30 psi at 3000) then it is time to look at bearing clearances.

Golden Jubilee
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Post Mon Jun 17, 2019 4:20 pm

Re: Oil Filter and Oil Pressure

Thanks guys, knowing all that makes me think I'm in pretty good shape with my engine oil pressure.
56 S120 4x4,

Golden Jubilee
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Post Mon Jun 17, 2019 4:57 pm

Re: Oil Filter and Oil Pressure

Thanks for clearing that 2 stroke mystery up, for me. I was under the impression the low to no oil pressure was because the oil had leaked out of the engine. The name Green-Leaker was well deserved. My employer had 1500 of them we kept topped up.
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Golden Jubilee
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Post Mon Jun 17, 2019 7:13 pm

Re: Oil Filter and Oil Pressure

JUST FOR THE FUN OF IT:
https://www.macsautoparts.com/ford_merc ... -only.html
the pictured mounting bracket is for a Flathead Ford V8. The bracket can be discarded and replaced with an owner built bracket/adapter to fit a different application. This filter unit could be mounted remote on a firewall and connected with oil resistant hose.
I would prefer to see the flow restrictors mounted in the block oil passage outlet, rather than at the filter.
The oil that returns to the oilpan does not enter the pressurised lubrication system.
Attachments
bypass restrictor.png
bypass oil flow restrictors
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Golden Jubilee
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Post Mon Jun 17, 2019 7:23 pm

Re: Oil Filter and Oil Pressure

I had 2 6-71's neither of them leaked. Very little out the slobber tubes, I've had 855 Cummins put more oil on the ground then they did.
V8's always seamed to leak.

Golden Jubilee
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Post Mon Jun 17, 2019 7:38 pm

Re: Oil Filter and Oil Pressure

To be clear, and fair, some heavy diesels do use a bypass system like Dean describes, The Cummins Big Cam 3 comes to mind. They have a piston pressure valve that opens to the bypass filter when the pressure rises but they flow a lot more thru the bypass filter then the engines we are talking about.
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