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it is a pressure sensitive unit in the side of the block that register oil pressure in the oil galleys of the engine
in vehicles with an oil light only it will switch off once a preset pressure is reached and turn back on when the oil pressure falls below that pressure
on other vehicles with an oil pressure gauge, it is a variable resistor unit that changes the resistance of the power from the gauge as the oil pressure fluctuates so altering the reading on the gauge
it is a different unit to an oil pressure sensor which conveys readings to the ECM
Suggest you find a garage/auto repair who will remove the oil pressure sending unit on the motor and insert a oil pressure gauge and read the pressure. Sounds like you have either a bad sending unit or maybe a plugged up oil filter. You are changing your motor oil every several thousand miles, right? Be blessed.
If you check the oil pressure with a mechanical gauge and the pressure is steady, the problem would be in the gauge on the dash if you have replaced the sending unit and there are no problems with the circuit. The mechanical gauge could verify a problem with the actual pressure in the engine.
oil sending units go out occasionaly and dont really mess anything up other than leaking oil on the ground just make sure you have the correct amount of oil in the motor and youll be fine. i just changed mine it quit working around 75,000 miles and i helped change my friends on his dodge he was around 87,000 miles. we both done this last year and no problems have come from it....
Sounds to me like it could be a bad oil sending unit or gauge. I would take it in to a shop and have them test the oil pressure with their equipment.
If they tell you the pressure is good try changing the oil sending unit first then if that don't work, replace the gauge.
Intake gasket has nothing to do with oil pressure unless you have coolant in the oil. Several items in play here...You either have a poor connection at the pressure sending unit, the pressure sender wire is chafed and grounding, the sender itself is failing or the oil pickup screen on the pump is partially blocked with loose carbon debris. I'd replace the sending unit first as they are inexpensive. If the problem continues then do some testing. A mechanical gauge can be put in place of the sender. That will tell you what the actual pressure is. If actual pressure is normal and does not fluctuate as does the dash gauge, then the problem is in the wiring. If the mechanical gauge reads the same as the one on the dash, then the problem is inside the engine and will need some teardown to find the reason. If the pressure does not drop below 15-20 psi, you may want to add a quart of Marvel oil to the crankcase. Sometimes that will help dissolve internal deposits without causing further problems. (takes a few weeks though)
You'll need to determine if the oil pressure is actually changing, or if the sending unit or gauge is lying to you. Be certain the oil level is up to normal, then check the actual oil pressure with a test gauge. If the pressure varies (drops) at engine idle, perhaps your pressure bypass is defective, or perhaps the oil pump is worn. Testing with a known good pressure gauge should lead you in the right direction.
The oil pressure sending unit is a sensor with an internal diaphragm, if the internal diaphragm is damaged , or the line to the diaphragm is blocked you can get this kind of fluctuation on the oil pressure gauge.
The oil pressure value must be read by installing a mechanical gauge near to the oil pressure switch and checking the pressure.
If pressure is ok, replace the sending unit. If there is a real pressure drop, check the oil pump.
If you still get fluctualtion after replacing the oil pressure sending unit, replace the oil pressure gauge.
I believe your sending unit is located on the top of the block, towards the fire wall. You can get an inexpensive pressure test gauge and put in place of your sending unit. It should be a 1/4" NPT fitting. Does the pressure gauge fluctuate between low and high RPM? If so, chances are that your oil pump may need to be replaced.