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Decreasing engine oil pressure

Marcin

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Hi All

Sometimes I have problem with too low engine oil pressure. Sometimes when RPM go down below 500RPM my oil pressure indicator shows almost 0 (it is analog gauge with tip). It happens when I try turn turn steering wheel when car is stopped or changer gear to reverse.

Sometimes that extremely low pressure occurs also when car is leaning to the left. Sending unit is new. What is your advice - should I change oil pump?

The car is 1999 year, 4.0 SOHC.

Marcin
 
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2000StreetRod

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oil pressure switch

The oil pressure sending unit is merely an electrical switch that closes when the oil pressure exceeds about 5 psi (don't know exact number) and opens otherwise. I assume that you have recently replaced your oil filter so it is not clogged and that your oil level is normal.

Your problem may be electrical. Does your instrument cluster battery voltage gauge drop when the oil pressure drops? Have you checked the battery voltage when the engine is running to see if your alternator output is adequate?

How many miles on the engine? What weight and type of oil (synthetic)? Do you have a buildup of sludge in the engine causing the oil to accumulate in the heads and galley and not return to the oil pan?

With oil pressure actually being that low you might hear timing chain rattle and valve train clacking. I would be concerned about possible engine damage. If you can't find an electrical problem I suggest removing the oil pressure switch and connecting a mechanical oil pressure gauge to the port and read the actual pressure. If low, you might try an engine flush and oil change to see if that helps.

Replacing the oil pump is not easy. The oil pan and block cradle must be removed which is an unpleasant task when working under the vehicle.
 
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joecrna

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I know there are times when my SOHC idles at about 400 rpm when in gear but remember, this is very low. Im surprised anything (alternator, power stearing, AC) works at this point. Having said that, the correct oil pressure at idle for another vehicle I own is 4.6 psi, then 35-60 psi at 3000 rpm. Who can measure 4.6 psi? I wonder if your "idiot" lights come on when you say your pressure is low or did you just notice this on an aftermarket gage?
 
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Marcin

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Hi

The first thing is that my Explorer has gauge like this
images

so it is not only simple light. Oil pressure is almost "L".
I use oil Ford Formula F 0W30.

I had to replace crankshaft bearings - they were damaged I thought because of too low oil pressure. Car mileage is 80k miles.

Maybe to flush engine is good idea?

Marcin
 
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2000StreetRod

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glorified idiot light

Hi

The first thing is that my Explorer has gauge like this . . . so it is not only simple light. Oil pressure is almost "L".
I use oil Ford Formula F 0W30.

I had to replace crankshaft bearings - they were damaged I thought because of too low oil pressure. Car mileage is 80k miles.

Maybe to flush engine is good idea?

Marcin

If the indicator jumps from nothing to something then the oil pressure switch is being closed by oil pressure. The indicator is analog and will vary some because of varying battery voltage. If your engine speed is below 500 rpm then your alternator voltage is probably low resulting in a lower reading on the indicator. The sending unit is only a pressure sensitive switch and has been since the early 2nd generations came out. Do a search on "oil pressure switch" or something similar to learn more. I added an AutoMeter sending unit and indicator in my pillar pod so I could read actual oil pressure. See posts #41 and #43 of this thread: Oil pressure gauge

Was the oil pump replaced or rebuilt when the main bearings were replaced?

Why does your engine speed drop below 500 rpm?
 
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snoranger

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Dale's right. Its an "idiot gauge". It doesnt show the actual oil pressure, it just shows that you have oil pressure.

I would be trying to fix the low idle RPM problem. It seems your trying to fix a symptom, not the problem.
 
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Marcin

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Hi

Oil pump was not changed when they change main bearings. It may be interesting that they told me during bearing change that engine was repaired before (bearing were not nominal). So it seems possible that the engine still have the same oil problem.

RPM sometimes is below 500RPM when I start to move steering wheel on the parking or switch reverse gear on (sometimes engine stops then). Generally RPM is more or less 1000.

Another idea is that maybe indicator resistance depends on oil pressure so gauge is not so "idiot"?

Regards, Marcin
 
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SoNic67

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They stopped using real indicators for oil pressure in 1984. The ones that are now are just pressure switches.
I did add a mechancial pressure gauge on mine and find out that below 5PSI, the switch will go off and needle drop to zero. Actually, arround that 5PSI will pulsate, based on the variations of oil pressure.

Images of the switch and the analog transmitters below (small one is the switch, big one is a proportional sender for a 1984 F-150):

P1020200.png
P1020206.png


And the analog pressure gauge with engine warm, low idle - at that level the needels where flickering.
P1030578.png
 
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my98nnj

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Another idea is that maybe indicator resistance depends on oil pressure so gauge is not so "idiot"?

No, it's an IDIOT gauge, it's either ON or OFF it does not indicate variable pressure.

Your low idle speed may be causing a low voltage issue which in turn is causing the gauge to dip. Fix the low idle, verify proper voltage (13.5 - 14) while the engine is at idle in gear. If the voltage drops below the specified range, you might have a weak alternator or battery, cable, connection issue.
 
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joecrna

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It does seem that his engine is going through bearings awfully fast, 80k miles. Factory gauge is just a deacorration for an "idiot" light though. You guys say that your trucks idle higher than 500 rpm when in gear. Mine never has. As I said originally, at times (AC on, leaving a parking space with wheel turned sharp) it will drop to 400. Obviously its not stable and will occasionally stall at this point. However, it never idles above 600 rpm exept when very cold out. What do you all think is a "normal" idle speed for a SOHC?
 
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SoNic67

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I would check the IAC valve first... That "sets" the idle rpm's.
 
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