Strange oil pressure activity - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-21-2008, 02:21 PM   #1
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Default Strange oil pressure activity

So I realize these are stock gauges and if it continues to be a problem I will get a mechanic to verify it for me and replace the sending unit if need-be, but has anyone heard of this...?

This is the first time I've noticed this happening, but it'* also the first time I sat in traffic fooorreverrr with this car. It always starts and runs like a dream () with the oil pressure ~60ish comfortably.

Suddenly when I looked over (still in traffic), I see it jiggling around 35ish. It'* pretty jittery down there, but not fluctuating much. When I give it some gas, it shoots right up with the RPMs to reach its normal level and caps there. when I let off the gas, it follows the drop in RPMs back to 35ish. The old girl did had jittery pressure like that the whole drive home that day as well. Just some strange activity I've never experienced...

When I started her up today and let her get to regular temperature, she seems go to 80, then slowly drop as she gains regular temperature but doesn't drop like that again at full temp... but again the engine wasn't running nearly as long either.

NOTE: It was a warmer yesterday than usual (or at least the sun was bright and hot but wind was cool) as well. Could that affect it?
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Old 03-21-2008, 02:35 PM   #2
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sounds completely normal to me.
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Old 03-21-2008, 02:56 PM   #3
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heh well i guess i'm just a bonne noob.

I'm actually pretty intelligent with reasoning of engine dynamics and whatnot, i guess I've just never noticed an oil pressure gauge on a car that'* so responsive. guess i always thought they seemed (or should be) static at normal operating temp, along with the electric and temp gauges.

Thanks anyway Haro!
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Old 03-21-2008, 03:03 PM   #4
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it all depents on what oil and filter you are running, the engine RPM'* and what load is on the engine. At startup on a cold engine 60psi is normal. When you get up to temp crusing down the highway at 60mph, 40-50psi is normal. When you are stopped at a red light with the car in gear, 30-35psi is normal. Try putting it in Neutral when you are at the stoplight to take the load off the engine and watch the psi rise a bit.
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Old 03-21-2008, 06:26 PM   #5
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Ah, I did that actually. I'm actually pretty accustomed to driving a standard, so I tend to shift into neutral even in an automatic when sitting in place for long periods of time (It'* weird, I know) and I can't drive a console shifter without keeping one hand on it these days. luckily my car'* not one.
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Old 03-21-2008, 06:30 PM   #6
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Just to back up what'* already been said, I experience similar things on my '93. For example, one time I got off the highway, drove another mile or two, and when I parked it, it was registering about 30-35 psi. Otherwise, it never dips below 45. Just very odd and random. Might have been due for an oil change too though.
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Old 03-22-2008, 07:15 PM   #7
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I had sort of the opposite problem - at around 110K miles the oil pressure was rising. It was not pegging the high limit, but close. It would drop a little when it warmed up, but it was still way high.

I changed the filter and the sending unit. No pressure change. I took the filter mount off, cleaned the pressure regulator spring and plunger. (they were not very dirty) Still no change. Took it to the dealer for a special "system flush". Still no change.

Took the filter mount housing off again and replaced the spring with a similar one I had just laying around the garage. That solved the problem. Oil pressure back to normal. Not sure why.

That was 6 years ago and I just turned over 200K miles. Oil pressure has been fine ever since...
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Old 03-23-2008, 02:21 PM   #8
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Our oil pressure gauges tend to be flaky. On my 96 its around 45-50 at cold startup, and on a hot day at idle in gear it will be about 20 psi at idle, but no lower. My 93 registers the same behavior.
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Old 03-23-2008, 03:13 PM   #9
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Quote:
Originally Posted by red454

Took the filter mount housing off again and replaced the spring with a similar one I had just laying around the garage. That solved the problem. Oil pressure back to normal. Not sure why.

That was 6 years ago and I just turned over 200K miles. Oil pressure has been fine ever since...
Spring rate, diameter, number of coils, compressed length, etc all have a bearing on this. I think it'* safe to say your oil pressure is simply dictated by the spring, in the same manner as the INTENSE oil pressure kit does it. You want to be careful not to use this procedure for a bandaid on a car that already has low pressure. It'* only delaying the inevitable.
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Old 03-23-2008, 08:16 PM   #10
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Oh - I absolutely agree - and while trying to make sense of it, I was expecting something really bad was happening in the engine. I thought maybe a bearing had spun and was blocking an oil port. I hooked up a mechanical gauge and confirmed what the dash gauge was telling me.

Nothing made sense. I consulted with two dealer service managers and one seasoned mechanic. They were all baffled. And I still don't understand what the problem was with the factory spring. If a coil had broken, I would have expected to see a pressure drop. If the plunger bore was packed with crud, then maybe that would explain the high pressure.

But it was clean. I have a box of springs and dug through it until I found one similar and figured what the heck - and gave it a try. Now I don't recall the coil count or wire dia. but it was similar in size and fit the physical constraints of the original.

The pressure has been in the normal range ever since. And that was nearly 100K ago...
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