My oil pressure gauge is acting like a tachometer?

[LeSabreUltra]

Can't say it's ever done this before...

I was driving it today, and I don't think it was doing this initially...but then again I wasn't really paying attention either...but when I looked down I noticed that it was sweeping back and forth with engine rpms. It never dipped below 40, but it would push 90-100 psi before shifting, and I wasn't pushing it hard, maybe 2500 rpms or so. I think at idle it would dip down to 40-50 psi but I can't really remember. I had been driving it maybe 10-15 minutes when this happened. It never pegged 120 psi that I could see. It's pretty warm outside, maybe 65 degrees, and I had driven it earlier in the day so the oil was fairly warm, however when I started the car it had cooled off enough that it was operating in open loop.

It continued to do that for a while, but it got more and more subdued as time went on. I was actually on my way to Advance Auto to get some motor oil for an upcoming oil change. Instead I returned here to go get my camera to take a video for you guys, but by then my OP had returned to normal. It still shifted with rpms, varying between 40-65 psi over a range of 600-2500 rpms. That's pretty normal for it, I've always had pretty responsive oil pressure, but not 100 psi responsive, lol.

I should have used the video recorder in my phone, but oh well.

5k on Mobil 1 currently. Oil is pretty dark but my OLM hasn't set the change oil soon light yet.

What do you think might be happening here? Dying oil pressure sender? Sludge? My car is becoming sentient?
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[Jrs3800]

Your oil pressure sender is starting to fail...

[LeSabreUltra]

Cool, perfect timing then. I'll get one and replace it when I change my oil.

Where is it located, generally? Will I need a gasket for it or does the new part usually come with one?

Thanks Don.
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[willwren]

Buy an AC Delco sender ONLY. I've used 2 other brands and both sucked within a month.

It's down on the back of the passenger side of the engine above your oil filter. Screwed into the back of the oil filter adapter. Just above where your axle exits the tailshaft housing on the passenger side. The sensor screws in from the rear of the engine. You can't miss it from underneath.

[LeSabreUltra]

Thanks for the tip, I'll go pick up some Pennzoil Platinum and a Purolator P1 later, cause I can get a pretty good deal on it at Advance Auto right now but I'll pass on their aftermarket brand.

On Rock Auto, they have an "Oil Pressure Switch" listed but not a sending unit. This is the picture they have associated with the AC Delco switch.



Is that what I need?

Description "SWITCH,F/PMP & ENG OIL PRESS IND w/SPEEDO & TRIP ODOM(U23)"
Part # 25535479
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[00Beast]

That switch looks right, but it's been a while since I've seen one up close.

[myfirstbonnie]

Yes, that is the one you want.

[LeSabreUltra]

Great, thanks. I'll pop it in there and see what happens.
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[Pontiac1]

ACDELCO Part # 25627057
SENSOR,F/PMP SW & ENG OIL PRESS GA w/GA(UB3) +
I would look again at the rock auto website,they list the correct part as a fuel pump pressure switch,I had to re-order because the first one I got was too short and made for a car without gauges,just a heads up.

[J Wikoff]

A couple years ago, I ordered one from RockAuto. Got a box labeled with the right number, but it was the wrong sensor (the short one). Emailed them, and they sent a replacement. Again, it was the wrong sensor in the right box. At that point they gave me a refund. I'm left with two sensors that I can't use, and not sure what can use them. Maybe it's the same batch and they never fixed it?