Oil Pressure - Fluctuating, dangerously - Experts please - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-14-2007, 10:33 AM   #1
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Default Oil Pressure - Fluctuating, dangerously - Experts please

New motor w/30k on it
Just had new trans swapped in.

I did notice this a little before, but it seems worse now.

Got the car back from the trans swap, thought I heard lifter tick (not positive what that sounds like). Also saw knock counts on my AutoTap.

Drained Oil, didn't appear to have any coolant in it. Threw in some Mobil 1 Synthetic, w/ some Mobile 1 "more expensive" filter-- was kinda limited as to the choices.

Now, it is like 1' outside.

However, my oil pressure gauge, which has constantly fluctuated some, seems to do it more. I don't know how to read the 0-40-120 gauge, but at lower speeds (or gears?) it will drop down to just above the 40 mark. This morning, driving about 50mph, in D, the gauge climbed alarmingly "one line" away from 120.

Concerned, I let off the gas, which brought it back down some, and just being curious, I put it into 3rd, pressure dropped a lot more.

City driving the gauge is constantly moving all over, but never quite seems to get as high as near the 120 mark.

So--- what am I looking at here? I should add I replaced the transmission after burning what was left of it trying to get my car out of a snow bank. The oil pressure, agian, always fluctuated, even before this.

Oil pump?
Type of oil (10w-30 syn)
Oil pressure relief spring.
When doing the trans, the guy said (can't remember why), that he needed to replace the oil sensor, because it was damaged or something- probably had something to do with some debris in the snow bank, when I was pulling it out.
Other mechanical problem?

What about the knock counts? Related?

Could the rebuilt trans being doing anything somehow, interfering with the oil pressure? Don't see how...

Anyone?

Thanks!

Daron
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Old 02-14-2007, 11:06 AM   #2
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To start off, it'* good that low speeds/idle you are seeing just over 40psi. that is very normal. It will increase with rpm and decrease with less rpm. Because the pump is driven off the crank, it is "driven" in a sense by the rpm.

As for getting up near 120psi, this could be a simple oil pressure sender or it could be a pressure relief valve. The valves don't fail very often and my first suggestion would be to check/change the oil pressure sender.
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Old 02-14-2007, 12:02 PM   #3
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First, When the transmission was replaced, I thought the guy told me he had to replace the oil sender unit- unless it'* something else that was replaced? In the engine bay, lower right hand side (driver side) of the engine, below the coolant intake hose, there is a new brass colored 1 1/2 in wide cylinder shaped device, with a pigtail and wires going back into the harness. Is that the oil pressure sender? or... sensor...? same thing, two different things?

Second, would that explain the fluctuation, even at idle?

Third, what about the knock counts? Related?
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Old 02-14-2007, 01:16 PM   #4
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Knock shouldn't be related...and usually not critical like oil pressure .

Small fluctuations..yes.
Location yes..that'* the oil pressure sender. We see plenty of them fail and it'* suspect.
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Old 02-14-2007, 02:00 PM   #5
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First step would be to determine what is the actual oil pressure of the motor. Chasing an electrical gremlin is different on the priority scale of a problematic oil pump/pickup.

Hooking up a mechanical oil pressure gauge would be the best but not the easiest in your garage. I'd say a combination of scanning the car with trying a different oil pressure sender should give you the most information with the least amount of work.
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Old 02-14-2007, 03:03 PM   #6
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Quote:
Originally Posted by Daron97SSE
First, When the transmission was replaced, I thought the guy told me he had to replace the oil sender unit- unless it'* something else that was replaced? In the engine bay, lower right hand side (driver side) of the engine, below the coolant intake hose, there is a new brass colored 1 1/2 in wide cylinder shaped device, with a pigtail and wires going back into the harness. Is that the oil pressure sender? or... sensor...? same thing, two different things?

Second, would that explain the fluctuation, even at idle?

Third, what about the knock counts? Related?
What you described is the coolant temperature sensor, not the oil pressure sensor.

The oil pressure sensor is on the passenger side of the engine, below the power steering pump.
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Old 02-14-2007, 03:08 PM   #7
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it'* not directly under the coolant intake hose/tstat... its farther down the block
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Old 02-14-2007, 03:52 PM   #8
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Actually... it sounds like location I agreed to isn't 100%

The oil pressure sensor right above the oil fillter
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Old 02-14-2007, 03:55 PM   #9
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no wait

take it back

just went and looked at it

this valve or switch is located on the side of the block (towards the radiator), with a vacuum line attached to it. One end goes to the EVAP, one goes off towards the fuel rail, etc

Unless this is a transmission part?

And again, the guy told me they replaced the oil pressure "switch"
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Old 02-14-2007, 04:02 PM   #10
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No, that'* ...uh.. got a picture?
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