OIl Pressure Change with Bypass Installation

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I installed a bypass filter kit onto my '86 F-250, 6.9L diesel. I installed the unit with the flow coming off the oil gallery in the block, very near the inflow from the oil filter, and the return goes into the oil filler tube on the timing gear cover. The unit comes with a .040 restrictor, which is installed. The oil pressure gauge sender is plumbed into same gallery about 8 inches away. I noticed a small drop on the oil pressure gauge. The gauge is one of those without numbers, but it does read actual pressure but the needle just moves within a ranged denoted "Normal." I would kinda expect to see some drop at idle but but it's lower by about the same amount at all rpms. I have not hooked a second gauge up yet (mostly because I used that easily accessed port for the filter), but based on my previous testing with an external gauge, I think it's dropped by around 5 psi, which would still put it well above the minimum number listed by the engine manufacturer. Any thoughts... Gary.... anyone? Is a slight drop somewhat "normal?"
 
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I'm sure it's related to your feed point being so close to the pressure sensor. I have not heard of this before - we can contact tech support at amsoil and ask - they certainly would know.
 

Jim Allen

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Well, I checked the pressure with a mechanical gauge and guess I was "chicken-littling" myself. The gauge is lower but the pressure is still very good and above "normal" levels. I could temporarily block off the filter and check again but the gauge numbers are very close to what I got when I checked a few years back (to see if there were any pressure changed between 15W40 and 10W30), so I will no longer worry about it. It could well be the sending unit because it seems a little erratic. On cold start, when the temporary gauge was reading 50 psi, the dash gauge was reading at the low end of normal. After the engine was warm and the mechanical gauge was reading 20 psi at idle, the dash gauge was closer to the center.
 
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I have a '94 Ford diesel and I know the factory gauge will read in the "normal" range so long as it sees 7 psi oil pressure. With your erratic readings, sounds like yours might be similar.
 

Jim Allen

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On my'86 IDI engine, it supposed to be a "real" gauge and it does react to changes in pressure but, lately, not the way I expect.
 
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Although I never installed it, I bought a check valve to install in my bypass to keep the pressure up. I searched for on with a "cracking pressure" of around 15psi, which should not allow oil to pass at pressures under 15 psi and therefore not starve the engine.
 
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 Quote:
Any thoughts... Gary.... anyone? Is a slight drop somewhat "normal?"
I suppose it's possible, but with a .040 restrictor I have a hard time figuring a measurable drop in reading. That system has a very high volume potential. The full flow is rated for around 30 gallons. If you have a real gauge, it should respond to engine speed. If it's mostly numb, then I would suspect it is an idiot needle. I think that they even engineered it so that as the wire warmed, it would allow a lower reading. The only way to tell is to verify it with a mechanical, as was mentioned (I think).
 
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Depending on engine wear and oil pump condition, any oil used for 'other' purposes will reduce flow&pressure in the rest of the engine. Now, a robust diesel engine should have plenty of surplus oil flow so it isn't something to worry about. Simply use a .030 orifice and see if you notice any changes.
 

Jim Allen

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I should add as a followup that when I unplugged the oil sending unit and cleaned the connector, the gauge began to read as normal. I guess the gauge malfunction was what my dad used to call a "co-inki-dinki." But one perfectly timed to get my bowels needlessly achurning.
 
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 Originally Posted By: Jim Allen
I should add as a followup that when I unplugged the oil sending unit and cleaned the connector, the gauge began to read as normal. I guess the gauge malfunction was what my dad used to call a "co-inki-dinki." But one perfectly timed to get my bowels needlessly achurning.
You should do like I did and replace every sensor on the engine, and vacuum lines. I cleaned every connector, as well. Made a huge difference in drivability and fuel economy.
 
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