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Thread: How Do I Verify Oil Pressure?

  1. #1
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    Default How Do I Verify Oil Pressure?

    Is there an easy way to verify what my oil pressure gauge is reading? I installed a remote oil pressure sensor, wired up to a light on my dash. The remote sensor is *supposed* to be calibrated at 20psi. However, according to my stock, dash gauge, the extra light I installed comes on once the pressure drops to about 30-32 psi. I'd like to figure out which is correct - the stock, dash gauge or the new, remote sensor.

    This picture shows the oil pressure sensor (blue shrink wrap):

    1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor

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    Ahhhh one of my personal questionable and still not satisfied understanding of oil flow specifics.

    How long have you been running the warning light and has it worked as intended before?

    You could rig up a cheap mechanical guage to that port and see what it sees for pressure. That would diagnose the warning light function. Depending on speed of switch see below.

    Find out specifics for the switch function does warning light come on at instant of 19.99 psi and or 2-3 seconds of <20 psi and it turns off with 2-3 seconds of >20 psi etc that might make a difference. Are you measuring the pressure pre or post filter media? That could dampen pressure spikes of oil flow especially as media plugs more. My guess is the complex flow path and bypass valves are messin with the light. If you measure downstream of filter and bypass's in an oil gallery I bet your oil pressure is close to what your dash gauge reads.

    I personally don't believe 100% of the oil goes through the filter or cooler for that matter in normal driving 100% of the time. But I won't tangent for now until I understand more of your problem.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

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    Also explain how its worked so far.

    I interpret light goes out when dash gauge reads above 32 psi. Is that cold and you are reading what about 60 psi idling then warm it dips to 30 ish psi idling and up to 50-60ish at 2000 rpm the light goes on and off depending on what???
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  4. #4
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    Couple of things to consider:

    The oil pressure depends in part on where you measure it. Don't expect 2 sensors at different places in the engine to read the same.

    The switch turns on and off in response to changing pressure. The gauge may respond more or less slowly to the same changes.

    10 psi at idle is more than enough. 45 psi is more than enough for all operations.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
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  5. #5
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    What size hoses are you running to the filter?
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    One thing I hesitate to question is how does that pressure switch work? Because I don't know exactly. Is it one wire one terminal or is it 2 hard to tell from pic looks like one wire and its suppose to ground to achieve ok signal. But looks like you have rubber for shock absorbtion in mounting filter head and again inbetween mount fixture and truck body so can it achieve good ground or is it open without vibrations or intermittents ???
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  7. #7
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    Quote Originally Posted by Hubert View Post
    One thing I hesitate to question is how does that pressure switch work? Because I don't know exactly. Is it one wire one terminal or is it 2 hard to tell from pic looks like one wire and its suppose to ground to achieve ok signal. But looks like you have rubber for shock absorbtion in mounting filter head and again inbetween mount fixture and truck body so can it achieve good ground or is it open without vibrations or intermittents ???
    Well, that's a good point - and a mighty keen eye, as well! Yes, it is a one-wire hookup. Yes, there is a rubber gasket between the mounts for vibration dampening. However, I think it ends up grounding through the SS lines. Now, I must say that this was not my intention. When I put this together I was well aware of how it's supposed to ground, but in the process I simply overlooked that step. Looks like I got lucky, 'cause the light on the dash seems to be working quite well - never any "intermittent" on time to indicate bad grounding. At night, it's awful bright! By the way, with the install of the new engine I cleaned all ground mounting points, replaced all ground straps with new/larger ones, and replaced all battery cables with 1-gauge. I even replaced the + cable that goes from the driver's battery to the main fuse box with a new cable about 2 sizes larger.

    OK, here's some more detail. I used -8 hoses as I was concerned about -10 possibly causing a slight drop in oil pressure. To keep things simple, I'll refer to things as "DG" (the PSI reading at the "Dash Gauge") or "RL" ("Red Light" on the dash, wired to the remote sensor).

    I just recently hooked this up with the install of the new engine (less than a week ago) - although I have been using the remote oil filter for some time, just not the oil pressure sensor. So, I don't have a comparison. What I can say, is the DG seems to operate the same as it did before. Meaning, how quickly the needle reacts/the extent of the high and low swings/what the PSI reads when the engine is cold or warm/how the needle reacts to RPM's. So it seems as the DG is operating exactly the same as before.

    At cold idle, the DG reads close to 60. At warm idle, it reads about 25. So once the engine warms up, then the RL will come on at idle. After the engine is warm, if I increase the RPM's to about 900 the RL will go out. This corresponds to about 32 PSI on the DG. The RL will come on and off very quickly - faster than the needle swings.

    By the way, the pressure sensor is actually located in an "IN" port on the filter mount as I'm intending the other "OUT" port for a bypass filter. However, my thought was there should still be the same pressure at the "IN" port since fluid takes the path of least resistance. I discussed this with a guy at my local injection shop and we both agreed. Does this make sense or am I missing something?

    I guess what I need to do to really know for sure is hook up a mechanical gauge (as suggested above) where the sensor is? Is there a better place to hook up a gauge?

    Sorry for the long reply!

    This is the filter mount: http://static.summitracing.com/globa...prm-1793_w.jpg
    1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor

  8. #8
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    The -8 lines should be fine. A -10 should not drop psi as it's just a vessel carrying oil to the point of leak which is the bearings...
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  9. #9
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    I am very interested in the outcome of this. I THINK the oil filter bypass valve is the reason the light comes on and its normal. Probably a bit less oil goes through your remote mount but its still operating as intended and ok.

    I think for the scope of engine oil passages pressure should still be higher upstream than down stream. As flow will take path of least resistance.

    OK JMHO lots of thought and some looking into.... I think the oil filter bypass valve works 2 ways:
    1. As a direct path pressure relief bypass. (At low flow and/or lower pressure)
    2. As check valve with a differential pressure release across filter media. (at higher flow and/or higher backside pressures).

    OR it provides for a minium of 17-19 psi differential to the filter media not sure exactly what is going on here. Its a parallel path of oil flow for sure with a checkvalve and restriction.....

    Looking at it its a built like a check valve and a direct pressure release with a spring. It has differing piston face sizes exposed to the check valve sealing piston/operation. So that on initial exposure to flow it opens at about 17-19 psi but once flow stabilizes it will shut and stay shut until some larger differential and or check valve operation opens it due to plugged media. I can't remember I tried back of envelope calculation and wasn't sure of outcome on differential pressure release opening (I think it varies according to backpressure somehow and or flow properties). But to me it has 2 modes of bypass direct and differential checkvalve of sometype. In actual operation it will open at plugged media and it also won't restrict oil flow to main galleries at low oil flow. I think its a simple neat little mechanism operation hard to explain with text.

    The oil pump pumps volume of oil depending on rpm. Oil pressure will rise as a restriction to oil flow downstream.

    At idle the OP supplies enough volume of oil to build approx 20-35 psi at the oil gallery warm due to the size of bearing clearances and remainder of oil path vs the volume of oil supplied at RPM. --- Increase the RPM ( OP flow volume) and oil pressure goes up as restriction to flow downstream. But the oil gallery doesn't care where oil came from.

    So here is what flow does oil pump is pumping and it bypasses filter because not enough backside pressure on bypass valve to hold it shut but the orifice size in bypass is small it still restricts flow so some oil will go to filter too. Enough oil volume is pumping to build 32 psi at gallery but filter head see less than 20 psi because not sure but maybe 10-19 psi of oil pressure flow is bypassing with the valve.

    Now increase rpm more oil flow from the pump the orifice in the bypass valve is a restriction so pressure increases on flow to the filter head at that point. Now the filter head sees more than 20 psi and light goes out. Oil gallery sees more flow from bypass and filter so pressure reads >32 psi because downstream restrict stays the same.

    Cold the orifice size in bypass valve is such that filter head sees more than 20 psi light is off. As it warms more oil can go through bypass valve oil orifice and filter head sees less than 20 psi. Cold the down stream of oil gallery path sizes/clearances build 60 psi of oil pressure.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

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    I think your warning light is a safety and if you use a lower pressure switch say 10psi maybe 15 psi it will work as intended and you'll know a tinsy bit faster if you loose oil flow due to cooler or remote line to filter failure. You'll still have to watch oil pressure guage for safety but warning light will be a earlies catastrophic failure alert. Or put warning light at 20 psi in main oil gallery and that will work too until engine is old and won't maintain 20 psi oil pressure
    hmmm
    AND or also might alert you to bad DG or hot oil that drops below 20 psi.
    Last edited by Hubert; 02-27-2008 at 08:07.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  11. #11
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    I still get a bit confussed on actual operation of this bypass valve. It may open if greater than 19 psi differential is on filter media and provide some lesser retricted flow to bearings at low volume flow say at idling 32 psi dash guage. But due to its orifice size will always provide some restriction to flow bypass and push oil through filter too. So in which case why the spring is it just a checkvalve so oil won't drain back out of oil galleries?

    I have read marine gassers up the bypass spring pressure when running remote mount oil filters and wonder why and if its important to do so. I have seen oil bypass plugs too and wonder if they are dangerous for daily drivers as cold start up would see some reduced flow to bearings.

    Comments welcome.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  12. #12
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    OK, I think I'm pickin' up what you're puttin' down. If I'm understanding you correctly (and JohnC.), both the remote sensor and the DG are probably correct. It's just that the oil pressure is actually different at the remote sensor and wherever the sensor is for the DG (by the way, where is it?).

    I certainly would prefer that this red light doesn't come on all of the time. However, I would also prefer to keep the 20psi sensor instead of dropping down to 10 or 15 - simply as it would give me more "heads up" time.

    Where is this "oil gallery" that you speak of?
    1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor

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    The oil gallery is up in the valley of the motor feeds the cam bearings and or then mains etc There are 2 one for each side of V. The dash guage sensor is ported to one of the galleries (think its the left one) at the upper or rear of engine the poplular oil pressure switch I believe. I think Jim's pic of the AMG/GEP engine block differences points the port out.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  14. #14
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    I don't think the oil filter bypass valve should be bypassing under normal circumstances. If it is, unfiltered oil is getting to the engine.

    Put a mechanical gauge on both ports (one at a time) and get readings under comparable RPM and oil temperature and compare them. The accuracy of the gauge is not important; you're just trying to quantify the difference between the 2 positions. The panel gauge is nortoriously inaccurate; better for trend analysis than absolute readings.

    Unless they have come up with a new numbering system, a -10 hose is bigger than a -8 and would have less effect on pressure, not more, right?

    Having 2 oil pressure sensors is like having 2 watches. You'll never know for sure what time it is...

    Less than 20 psi at hot idle is not necessarily something to worry about.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
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    Quote Originally Posted by JohnC View Post

    Unless they have come up with a new numbering system, a -10 hose is bigger than a -8 and would have less effect on pressure, not more, right?
    Well, my thinking is that the larger the vessel (hose), the lower the pressure will drop. Same amount of fluid pumped through a larger tube will decrease pressure in the tube. -8 and -10 are awful close, so maybe the difference is negligible. As stated above, maybe it's not so much the size of the hose and more what's at the end of the hose that controls the pressure (unless we start exagerating the hose size).
    1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor

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    I don't disagree with that JohnC but stand behind all that I wrote. I have read lately that Ford's oil pressure gauges are "fake" and if minium oil pressure is measured the guage needle sits in middle. I thought GM's gauges were real psi measurement and not that fake and is in the ball park of accurate. Hopefully at least within 10-12 psi but have also always wondered about the specs being so low in relation to gauge.

    Would you or anyone care to comment on just how the bypass valve works? I would like to understand initial and steady state operation of flow.

    Not having 100% of oil filtered 100% of the time is more the reality from my research. Its the constant loop and refiltering that keeps the oil ok. Oil filters are not absolute filtration but multipass effeiciency is pretty good.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  17. #17
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    I asked Dr Lee this very question several years back, and, unless I missunderstood his answer, he said that the bypass should not open under normal circumstances.

    The purpose of the bypass is to prevent oil starvation should the filter become plugged, not to dampen momentary pressure variations. Seems to me the proper choice of valve would take normal pressure variations into account. Oil picks up its debris on the way back to the filter, not between the filter and it's appointed rounds (barring catastrophic failure), so there is no guaranty that oil from the sump doesn't have something damaging in it no matter how often it has been through the filter in the past. Seems like a bad bet to me!

    Dennis - I think the pressure-velocity relationship is inconsequential at these flow rates. Regardless, any pressure change in the lines is nullified once the oil reaches the filter. I'd go for the larger lines to cut down on frictional losses. Pressure lost due to flow changes can be recovered. Frictional losses are forever...

    The gauge on my '95 was not fake, I just don't think it was intended to be accurate. Besides, a 10 psi error is more than enough to account for the differences being discussed here.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

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    True and I need to rethink it AGAIN because I am not sure flow would not reverse some if gallery is at 32 and filter inlet was at 20 as oil pressure as in general flow travels from hi to low.

    More thoughts to come the oil bypass is killing me.
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  19. #19
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    Oil contamination is cumulative and continuous filtration removes the big stuff. You can run an engine on unfiltered oil ok for a while you can do partial filtration per loop and circulation and run a really long time (idea behind oilguard type systems). I think the amount of oil that actually gets filter is a bit of an unknown when running a remote mount filter with bypass not adjusted. Why have different bypass pressures?

    I can see the oil pressure being slightly higher in the oil gallery than the filter inlet due to the bypass but not excessively.

    Other ideas on how it works?
    97 5spd K2500 Ext Cab short Bed ~160K miles.
    TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.

  20. #20
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    BTW, good catch on the missing ground wire!

    The bypass valve opens in response to a differential pressure between the filter inlet and outlet. If the valve is open, then, by definition, the pressure at the filter outlet must be lower than the inlet. The outlet is plumbed directly to the gallery in question. No way the bypass can raise the gallery pressure above the pressure at the filter outlet. It's the salamander eating its tail...

    I might buy it if the bypass emptied into the opposite end of the gallery, but it doesn't. It empties right at the filter outlet, or, in this case, where the return hose enters the engine.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

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