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Oil Pressure Gauge Fluctuating

Ok… So I have a 2001 Mercury Grand Marquis. When I turn the car on the oil pressure gauge acts normally, but if I have been running it for awhile, and I pull up to a stoplight, or have to idle for any period of time while in Drive and not Neutral, my Oil pressure gauge will fluctuate slightly. It doesnt’ drop the whole way up and down, it just shimmies and shakes This is new for my car and I’m wondering if it’s a problem foretelling bad stuff down the road or just an older car with over 200,000 miles on it showing wear and tear. Thanks in advance for letting me know what might be wrong guys

One thing that can cause this problem is a defective oil pressure sensor.

It’s cheap and easy to replace.

If that doesn’t fix the problem, then a separate oil pressure gauge would be installed in place of the sensor to monitor the real oil pressure.


My Ford truck has an oil pressure gauge, and it holds pretty steady. It does tend to drift up and down +/- 10 psi or so over long periods of time, based on the engine oil temperature I think. But it doesn’t jitter. What I’d do is take it to a shop and ask them to use their shop oil pressure gauge to see if they notice anything like that with a calibrated known to be working gauge. If it doesn’t do that on the shop gauge, you know the problem is with the sensor, gauge, or other electronics between the two. Another idea, a faulty voltage regulator can cause this, either in the alternator, or the one that regulates the voltage to the dashboard electronics. My guess, most likely just the sensor or its connector.

Thank you. Would that cause it to only jump at Low RPMs though, which is
what mine does, or wouldn’t that make it jumpy all the time? Also is this
something I need to fix for the safety of my car, or because that gauge is
only a “feelgood” gauge anyway, is it fine the way it is?

do garages normally look at stuff like that for free? does your truck do
it while driving, or while stopped and idling?


The car has an oil pressure indicator but its only function is to operate like an idiot light. When the oil pressure rises to about 10 psi the gauge needle moves to the NORMAL position and remains there unless the gauge fails or oil pressure drops. There is no relationship between oil pressure rising and falling and the pressure indicated on the gauge but voltage rising and falling will cause the needle to rise and fall a barely noticeable amount.

There are youtube videos demonstrating how to clip a resistor out of the dash printed circuit and replace the on-off switch on the engine with the proper pressure sending unit in order to have a working oil pressure gauge.

I’m not worried about having a working oil pressure gauge. I just want
that needle to stop bouncing because it bothers me, and I want to know if
its an indication for a big or coming problem with my vehicle. What would
cause my voltage to be jumping around like that to make it happen, because
that sounds like my issue.

A cheap digital voltage gauge that plugs into a power outlet (cigarette lighter) is available at many parts stores and with it you can compare voltage variations to the movement of the gauge. But without a gauge you might try turning on a heavy electric load while idling and watching the oil pressure needle. Does your car have a working heated rear window? If so it will drop voltage significantly when on at idle.

It’s possible that the connection between the sensor and the wire coming off it is dirty and/or loose. When the engine is idling in gear it shakes more than at any other time, and the shaking will create a “hit or miss” contact in a poor connection. Next time you get your oil changed go to a real shop, not some “Hurry-Up Lube” place, and ask the mechanic to check out the connection at the pressure sensor.

Sorry to seem silly I just don’t know much about cars. Also my cigarette
lighter doesn’t work to be able to test that. I can see if that affects
the issue or makes it more prominent. But how do I fix the voltage problem
if it is an issue, and do I need to because it portends a bad problem for
my car in the future, or should it be ok for the next year that I want to
drive it.

Most parts stores will test the battery and charging system on your car for free in their parking lot if you go there when they aren’t busy. If you try that route I suggest you take your car to every nearby parts store in hopes of getting some consensus regarding the situation.

Your problem may be as simple as a corroded connection or as expensive as a new alternator if your problem actually is the result of fluctuating voltage. And no one knew anything about cars until they got under the hood and got greasy.

haha I do do some of my own work,and have been doing various work on the
spark plugs, ignition coils, etc, and some other things that can touch base
on the electrical system. I try my best and do what I can, I’m just not
super knowledgeable and I’m learning terms, etc. If it’s a voltage problem
would it be centered around my battery, or my sensor, or could it honeslty
be anywhere in the electrical system and just affecting that part. Also,
if I saw no other effects to my car other than that fluctuation, is it
something I would need to get fixed asap?

Thank you very much. I think I will have to do that. It sounds a lot like
what the issue may be, just a shake rattle and roll with a bad connection
in an older large car.

A practical approach would be to replace the suspect failing oil pressure switch and live with the results. If that doesn’t solve the problem it is not worth the expense of replacing the engine to get the oil pressure you would like to see.

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It would be best to verify that switch first @Nevada_545. In fact, just pulling the wiring pigtail off and checking for oil leaking from the top of the switch might be enough to confirm that the switch has failed. It is often oil leaking out to the spring side of the diaphragm and onto the contacts that result in failure. Maybe @savinimark can get lucky today.

Yes, verify but I would have a new switch in my hand before bending over to look at the old one.

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I agree it’s not worth the expense of a new engine. That’s for certain.
If it is just the oil pressure switch, is that something I will absolutely
need to fix, or will it just be causing that slight fluttering of the oil
pressure gauge. If it’s only the fluttering I can live with no fix. If it
will damage my car in the long term though I will fix it. I only want this
car to last me another 6-18 months.

So in short, you are saying cleaning/replacing the cheap oil pressure
switch should fix the issue. Are a switch and sensor the same thing in
this regard? If it does not, does that mean it’s a voltage issue. If it’s
voltage issue, what would my next step be, to look at my voltage
regulators? I just want to make sure I understand the exact 1.2.3. I should
do. Like i said, I’m capable of doing things on car, but don’t know enough
about terminology or have the innate knowledge to think next level.

It’s called an oil pressure sensor if there’s an oil pressure gauge, and It’s called an oil pressure switch if there’s an oil pressure light.

The oil pressure sensor is mounted to the engine block, next to the oil filter.


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