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Old 09-02-2004, 10:26 PM   #1
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oil pressure drops at idle raise right back up when cruising

My oil pressure when cruising acording to the dash gauge is at 30 psi or slightly above. once the car is run for 15 - 20 min and i stop at a light the gauge is at the first tick mark or slightly below(right before the red). as soon as i start driving again the oil pressure goes back to 30 psi . I have replaced the sending unit within the last 8 months because i was having this problem before. at the same time i replaced the sending unit i also changed my oil to 20 - 50 and have been using napa gold filters. After all that was done my car ran steadly at 30 psi ( or slightly higher) even during the hot summer days . yesterday it began to drop as described above again and it was only about 80 degress out. my oil was changed a little over 1000k miles ago (aprox 1.5 months). my car has 135K miles on it now. Do you think i should be concerned about this or is it just another bad sending unit.


BTW : I CAN'T HEAR ANY ABNORMAL NOISE COMMING FROM THE VALVETRAIN.

ANY HELP WOULD BE APPRECIATED
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Old 09-02-2004, 10:52 PM   #2
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You too huh?

Yeah, I have got the same issue. I also moved to a thicker oil, and my ticking goes away after the car has been running for a good 5 minutes or so.
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Old 09-02-2004, 10:54 PM   #3
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the warmer the engine usually lower the oil psi is.

every 1,000 rpm is around 10 psi is the norm. i think.

i would be happy with the guage going up when the rpms rise and goes down when u let off.

what does the guage read when u first start the engine up after the sitting for awhile... mines up to at least 50 because the oil is so thick and cold..
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Old 09-02-2004, 11:37 PM   #4
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my 350 reads 50 when the engine is off but when i start it, it goes up to 60 then when i get on it it goes up around 100? is that bad. the guage is not in the dash its a newer one and i recently changed the pressure line because it was old and had a crack in it. im alos using 20w 50 motor oil
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Old 09-03-2004, 01:59 AM   #5
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a good rule of thumb is 15 psi for every 1000 rpms. the moment you stomp on it, it should fly wayyyy over to the 50/60 mark lol. and if it doesn't... then you've got a problem you really don't need, or want for that matter.
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Old 09-03-2004, 02:08 AM   #6
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this is all well and good but the real issue is that it didn't used to do that before.

Right?
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Old 09-03-2004, 03:06 AM   #7
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ha

no my oil pressure as always been at 50 since ive changed the oil and the sending unit. guess thats just how its gunna read for me must be off or something reading 50 as zero and 100 as around 50+:werd:
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Old 09-03-2004, 03:08 AM   #8
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i'd say he's using too thin of an oil... but he's not.
he replaced the sending unit a few months back. maybe he needs to do it again. wouldn't hurt to do it just to illiminate it as a reason the oil guage is retarded. maybe you need to switch oil brands. what brand oil are you using now? i don't know if it'll work, but have you tried to add a qt of greased lightning or slick50?
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Old 09-03-2004, 01:16 PM   #9
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when i start my car up in the morn it reads just above 30 psi.

I am using castrol gtx dino oil
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Old 09-03-2004, 02:41 PM   #10
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its funny cause when i idle ruff my oil gage need has a ruff idle look to it.

but its normal to go up and down when im at idle 500-550 rpms (after engine is warm) its like dead center pointing west and when i hit the gas it goes up. kinda like a tach lol
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Old 09-03-2004, 09:39 PM   #11
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OIL PRESSURE

According to the specs book I have the oil pressure according to GM should be no less than 18 PSI at 2000 RPM and above.

I have had a slew of these cars with various engines. Some have had high pressure continually and others not, it all deals with the tolerances of the pump and the bearing clearances.

According to GM your pressure is fine for a stock application. I would not be worried about a problem unless the pressure hits the redline. Sending units dont go bad that quick so I bet the pressure is accurate. You could confirm with a mechanical guage if you wanted.

About the only way to raise the oil pressure would be to install a high pressure spring in the pump cover, or install a new oil pump...
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Old 09-05-2004, 03:46 PM   #12
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is there such thing as too much oil pressure though?

because as you increase pressure you decrease volume for the same orifice size.. obviously you want a bit to keep the whole system charged with oil but on high demand conditions, too much oil pressure will lessen the amount of oil coating your rotating parts..

anyone know?
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Old 09-12-2004, 04:01 PM   #13
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that would only be the case if you were increasing the oil pressure by decreasong the size of teh orafices. the "volume" of teh oil system galleries is difficult to change, and a loss in pressure is usually caused by a bad pump or pump cover spring.

I have never heard of too high oil pressure, although high pressure could be caused by tight bearing clearances i would imagine
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Old 09-12-2004, 04:01 PM
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