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VNMOUS · 06-03-2003, 10:36 AM

The oil pressure started fluxuating on the old 350.
when it is cold the idle pressure is at 60 lbs. and when it warms up it fluxuates from 40 lbs. to 20 lbs. When the pressure drops to around 20 lbs. there is a distinct peking noise in the engine. I first thought the screen had fallen in the oil pan but now I'm not sure. Any suggestions will be apreciated. The engine has about 2000 miles.

dubie · 06-03-2003, 10:43 AM

I have heard of faulty oil filters before that screw with your oil pressure. That might be a place to start is an oil change. Any leaking under the hood, like a rear main seal?

krue · 06-03-2003, 10:44 AM

I have heard that these engines could run with oil pressure as low as 5#. Does the noise at low pressure sound like the lifters clattering? I am definitely not an expert but it sounds like you need a new oil pump.

Professor · 06-03-2003, 12:19 PM

Could be the oil pump. Could be that the engine is just loosening up after the rebuild and its the looser tolerances in the mains and rod bearings.
Or it could be the relief valve (and spring) in your oil filter adapter. If I understand correctly, this is in the fitting that the oil filter screws onto and bypasses the filter if the pressure gets too high. If it is bad (or weak) can cause low pressure and bypassing the filter.

Professor · 06-03-2003, 12:24 PM

Could be the oil pump. Could be that the engine is just loosening up after the rebuild and its the looser tolerances in the mains and rod bearings.
Or it could be the relief valve (and spring) in your oil filter adapter. If I understand correctly, this is in the fitting that the oil filter screws onto and bypasses the filter if the pressure gets too high. If it is bad (or weak) can cause low pressure, plus bypassing the filter.

71GMC_3/4T · 06-03-2003, 01:07 PM

Mine was doing some weird stuff so I bought a new oil pump. Imagine my surprise when I pulled the pan and found the sump laying in the bottom of the pan, no longer attached to the pump!
Previous Idiot induced problem.
Unfortunately, I think it did some damage since I don't have oil pressure for squat any more. I'll run her till she pukes...
Definitely try the new oil filter approach first. Don't use a Fram! Wix or Purolator are good brands, as well as the Napa "house brand".

JimKshortstep4x4 · 06-03-2003, 01:14 PM

Fluxuating pressure probably indicates that your pump is cavitating. My suspusion would be a loose pump or the screen has fallen off as you had thought of.

I would not drive it and plan on pulling the pan to check things out.

Jim

tom hand · 06-03-2003, 05:09 PM

fluxuating between 20 at idle and 40 at cruzing speed is pretty normal oil pressure... are you sure you don't have a header leak? I have seen people adjust their valves a dozen times before they figured out they had a header leak

crazy longhorn · 06-03-2003, 07:40 PM

The oil pressure should not "dance", but should go steadily up as the rpms increase, & will also drop as the rpms drop. Figure about 10psi per 1000 rpms as a rule of thumb. I like to see 20 psi @ idle on a "tight stocker"(in gear)..... but steady up/down with the rpms. If its dancing, you have problems with a sticky bypass in the pump, a bad filter,pickup sucking air, or dropped off the pump(yikes). My experience says that if the gauge is bouncing.....you have problems! You might try another guage(aftermarket mechanical), to see if the guage or sender is the prob. Good luck,crazyL

VNMOUS · 06-04-2003, 08:26 AM

Thanks Guys
I pulled the oil pan last night and there laying in the bottom of the pan laid the screen. Any suggestions on how to keep this from happening again?

MAXMEOW · 06-04-2003, 06:14 PM

Check to see if there are two of the rubber "O" ring gaskets. One might be stuck up the oil pump shaft while the other looks normal on the pick up tube. You can tack weld the screen in place for added reliability.

06-03-2003, 10:36 AM	#1
VNMOUS Step Side's Rule Join Date: Feb 2002 Location: LEIGHTON,AL USA Posts: 227	Need Help Quick The oil pressure started fluxuating on the old 350. when it is cold the idle pressure is at 60 lbs. and when it warms up it fluxuates from 40 lbs. to 20 lbs. When the pressure drops to around 20 lbs. there is a distinct peking noise in the engine. I first thought the screen had fallen in the oil pan but now I'm not sure. Any suggestions will be apreciated. The engine has about 2000 miles. __________________ DANO 07 Silverado Classic 67shortstep 76 stingray 95 cobra 66 Mustang Coupe 289

06-03-2003, 10:43 AM	#2
dubie Registered User Join Date: May 2000 Location: Flin Flon, Manitoba, Canada Posts: 8,853	I have heard of faulty oil filters before that screw with your oil pressure. That might be a place to start is an oil change. Any leaking under the hood, like a rear main seal? __________________ My name's Tim and I'm a truckaholic My 56 Chevy shop truck build http://67-72chevytrucks.com/vboard/s...d.php?t=562795

06-03-2003, 10:44 AM	#3
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	I have heard that these engines could run with oil pressure as low as 5#. Does the noise at low pressure sound like the lifters clattering? I am definitely not an expert but it sounds like you need a new oil pump. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

06-03-2003, 01:07 PM	#6
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Mine was doing some weird stuff so I bought a new oil pump. Imagine my surprise when I pulled the pan and found the sump laying in the bottom of the pan, no longer attached to the pump! Previous Idiot induced problem. Unfortunately, I think it did some damage since I don't have oil pressure for squat any more. I'll run her till she pukes... Definitely try the new oil filter approach first. Don't use a Fram! Wix or Purolator are good brands, as well as the Napa "house brand". __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

06-03-2003, 05:09 PM	#8
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	fluxuating between 20 at idle and 40 at cruzing speed is pretty normal oil pressure... are you sure you don't have a header leak? I have seen people adjust their valves a dozen times before they figured out they had a header leak __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

06-03-2003, 12:19 PM	#4
Professor Registered User Join Date: Mar 2001 Location: Fayetteville, Arkansas Posts: 160	Could be the oil pump. Could be that the engine is just loosening up after the rebuild and its the looser tolerances in the mains and rod bearings. Or it could be the relief valve (and spring) in your oil filter adapter. If I understand correctly, this is in the fitting that the oil filter screws onto and bypasses the filter if the pressure gets too high. If it is bad (or weak) can cause low pressure and bypassing the filter.

06-03-2003, 12:24 PM	#5
Professor Registered User Join Date: Mar 2001 Location: Fayetteville, Arkansas Posts: 160	Could be the oil pump. Could be that the engine is just loosening up after the rebuild and its the looser tolerances in the mains and rod bearings. Or it could be the relief valve (and spring) in your oil filter adapter. If I understand correctly, this is in the fitting that the oil filter screws onto and bypasses the filter if the pressure gets too high. If it is bad (or weak) can cause low pressure, plus bypassing the filter.

06-03-2003, 01:14 PM	#7
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Fluxuating pressure probably indicates that your pump is cavitating. My suspusion would be a loose pump or the screen has fallen off as you had thought of. I would not drive it and plan on pulling the pan to check things out. Jim

06-03-2003, 07:40 PM	#9
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	The oil pressure should not "dance", but should go steadily up as the rpms increase, & will also drop as the rpms drop. Figure about 10psi per 1000 rpms as a rule of thumb. I like to see 20 psi @ idle on a "tight stocker"(in gear)..... but steady up/down with the rpms. If its dancing, you have problems with a sticky bypass in the pump, a bad filter,pickup sucking air, or dropped off the pump(yikes). My experience says that if the gauge is bouncing.....you have problems! You might try another guage(aftermarket mechanical), to see if the guage or sender is the prob. Good luck,crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

06-04-2003, 08:26 AM	#10
VNMOUS Step Side's Rule Join Date: Feb 2002 Location: LEIGHTON,AL USA Posts: 227	Thanks Guys I pulled the oil pan last night and there laying in the bottom of the pan laid the screen. Any suggestions on how to keep this from happening again? __________________ DANO 07 Silverado Classic 67shortstep 76 stingray 95 cobra 66 Mustang Coupe 289

06-04-2003, 06:14 PM	#11
MAXMEOW Registered User Join Date: Jun 2003 Location: las vegas nevada Posts: 3	Check to see if there are two of the rubber "O" ring gaskets. One might be stuck up the oil pump shaft while the other looks normal on the pick up tube. You can tack weld the screen in place for added reliability.



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