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Oil pressure drop on fillters...

Old 06-01-2007, 07:46 AM
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Question Oil pressure drop on fillters...

Anyone know the oil pressure drop across a Merc oil filter (the 1 qt, black filters)? I assume oil pressure sender measures oil pressure after the filter?

Anyone have an oil routing schematic just to become familiar with the system?
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Old 06-01-2007, 10:11 AM
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The oil drop through just about anyfilter will be a max of what the pressure relief spring in the block is rated at , usually either 11 or 30 psi depending on the relief installed.
Any clogged or damaged filter will drop to these levels where the pressure relief will open and the resulting pressure will be dropped by these amounts, however at this point no filtering is taking place which is dangerous for the motor!
Most clean filters depending on size and media type will drop pressure about 3-6 psi versus no filter at all in the system. This of course will depend on the type and condition of the oil pump, oil viscosity used, and overall condtion of the engine and bearings. Now that I have thoroughly confused everyone, just keep a clean quality filter installed with good oil and don't worry about it unless you have an oil pressure problem.

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Ray @ Raylar
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Old 06-01-2007, 10:20 AM
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Originally Posted by Raylar
The oil drop through just about anyfilter will be a max of what the pressure relief spring in the block is rated at , usually either 11 or 30 psi depending on the relief installed.
Any clogged or damaged filter will drop to these levels where the pressure relief will open and the resulting pressure will be dropped by these amounts, however at this point no filtering is taking place which is dangerous for the motor!
Most clean filters depending on size and media type will drop pressure about 3-6 psi versus no filter at all in the system. This of course will depend on the type and condition of the oil pump, oil viscosity used, and overall condtion of the engine and bearings. Now that I have thoroughly confused everyone, just keep a clean quality filter installed with good oil and don't worry about it unless you have an oil pressure problem.

Regards,
Ray @ Raylar
Ray,

Was trying to get an idea of what the filter deltaP would be. I am running 50wt full synthetic Royal Purple. A clean, new filter should not be bypassing, but will see a pressure drop.

If it's bypassing, engine oil pressure should read low at the gauge, correct? (ie. 50psi at the pump, 30psi if bypassing, would read 20psi at the gauge/sender which is after the filter base?) If not bypassing and 50psi at the pump, then should be slightly under the 50psi after the filter.

I am trying to discern if 50wt petroleum based oil will act the same as 50wt full synthetic. Afterall, they are both 50wt. So, shouldn't they both read the same on the gauge? Or is synthetic that much easier to flow and would read less gauge pressure?
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Old 06-01-2007, 11:59 AM
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Originally Posted by razor1115
.

I am trying to discern if 50wt petroleum based oil will act the same as 50wt full synthetic. Afterall, they are both 50wt. So, shouldn't they both read the same on the gauge? Or is synthetic that much easier to flow and would read less gauge pressure?
In theory, they should act the same but...........different oils from different blenders are never the exact same viscosity even though they are both (in your case) 50wt. One blender may formulate to the low end on viscosity while another my go to the high side.
A product formulated on the low end of 50 will react like a really strong 40. While one on the high side will react like a weak 60.


Ken
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Old 06-01-2007, 03:00 PM
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Originally Posted by minxguy
In theory, they should act the same but...........different oils from different blenders are never the exact same viscosity even though they are both (in your case) 50wt. One blender may formulate to the low end on viscosity while another my go to the high side.
A product formulated on the low end of 50 will react like a really strong 40. While one on the high side will react like a weak 60.


Ken
So...how do you know what you are purchasing?
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Old 06-01-2007, 05:48 PM
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you buy good quality name brand oil in the viscosity that suits your clearences and keep it at between 220 and 240 deg and thats all there is too it. pressure drop thru any membrane (filter) is a function of viscosity and membrane density.... a 5 micron filter will have more pressure drop than a 10 micron etc... so it comes down to flow rates etc ... none of which really matters to us. that engineering has been done elsewhere by competent engineers. for we the consumer, if you are concerned, you do some subjective testing with a gage on either side of the housing... then you will know, in absolute terms, what the delta p is at a given temp w/ a given oil across as many filters as you choose to measure. my belief is that you will find precious little difference between any of the good name brands.

and i am still confused by all this talk of " clogged" filters.... i would suggest that if your filter has seen enough trash to be clogged then the root source of that trash is the cause of your engine failure... not the filter that caught it.
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Old 06-01-2007, 09:29 PM
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Good discussion and good points here. We just had a case where a new 496HO engine with one of our Raylar kits installed was put in a boat by an installer and the scan tool and the dash guage were both reading about 20psi at idle and about 40psi at 5000rpms with the engine oil and coolant at operating temperature. We felt this was a little lower than we normally see in these motors, where we normally see about 40psi at idle and 60psi at 5000 rpms with standard Mercury 20-40w oil at temperature. We reccommended that the motor not be used in the boat until the lower oil pressure problem could be investigated and corrected. We were pretty sure either the bypass was opening or an oil pump was in trouble. We did two things, one, we dropped the pan and checked the pump, everything was ok and looked good at the pump including the pressure relief valve in the pump. We then used a tool to cut open the oil filter and examine it and its contents (we should have done this first as its much easier.) Low and behold we found the media inside the filter coated with a sticky goo, that had "CLOGGED" the filter and hence the bypass was opening with the pressure buildup in the prefilter circut. What was the goo, were not sure but we suspect a contamination of the oil or filter before it was installed at the factory. In any event we drained all the oil, cleaned the oil system parts and replaced the filter and the oil pressure is now 40psi at idle and 60psi at 5000 rpms where we felt it should be. So the point here is that filter clogging can occur from things other than internal metals and debris from engine mechanical problems. This is why bypasses actually help protect oil starvation with filter or system obstructions. So know your motors normal operating oil pressures at idle and high rpms, hot and cold when all is well and if you see any substaintial change in those numbers when running the boat then reduce rpms and use and investigate to find the causes and hopefully avoid damage to expensive engine systems. Just some real world findings that may help preserve motors.

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Ray @ Raylar
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Old 06-01-2007, 09:53 PM
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Great discussion...and Ray, the "know your boat" is exactly what I'm investigating. I bought a new-to-me boat 4 weeks ago and run full syn oil in the engine. The pressure seems a little low, but it is that way on both engines. Originally, it was a touch higher before I did the oil change. The previous oil was Amsoil 20w50. I replaced with Royal Purple 50wt as there was no local dealer (I knew of at the time). That is why I was wondering if syn actually, somehow flows "better" even though they are the same weight. And would petroleum oil at 50wt act any different.

Pressure is a touch lower, but the same on both engines. Seeing 45psi warmed and up running. To me, that is a little low. I am learning all the nuances of the new ride...

45psi seems a little low. Would prefer to see 60. Engines are just redone and dynoed with~70hrs total use.
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Old 06-01-2007, 11:46 PM
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razor 1115:

I understand your question and both those oils are good product. I am surprised though you are using straight 50wt in the motor, that seems a bit to much viscosity as a single grade? If its a single 50wt grade when your motor is cold you might not be getting the best oil flow and protection you need. I feel that multi-grades of the 20-50w, 20-40w and such do an overall better protection as the motor goes through its temperature cycles. What pressures do you see at idle and what pressure at lets say 5000 rpms? Also obviously helpful to know a little spec on the motors, type, size, power levels, etc.

Thanks,
Ray @ Raylar
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Old 06-03-2007, 10:23 AM
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Originally Posted by razor1115
So...how do you know what you are purchasing?
You don't. You hope that the oil blender has morals and is building a legit product,......or, you can have a viscosity check done on your oil before you install it in the boat by an oil lab, or you can just ask the manufacture of the oil what are the typical inspections of the product you intend to use.

Ken
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