Low oil pressure

Tiny
BEP123@YAHOO.COM
  • MEMBER
  • 2006 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 92,000 MILES
'Has low oil pressure at idle/stop. Gauge goes to 8lbs, chimes go off. PSI's go up as RPM's go up. Truck is making no noise and no smoke. Changed the sending unit. Mech. Gauge shows low pressure as well. What could be cause of low pressure? Do these engines have plastic check valves?
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Wednesday, December 22nd, 2010 AT 5:13 PM

36 Replies

Tiny
JDL
  • EXPERT
My info shows 6 psi@1000rpms. Shows 18 psi@2000rpms. MOD shows these specs. They are probably minimum specs, so the reading could be a little higher. These databases are not always correct, but, I don't carry these specs in my head, so I have to look it up.
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Wednesday, December 22nd, 2010 AT 5:43 PM
Tiny
CWALBY
  • MEMBER
  • 2005 CHEVROLET SILVERADO
  • 6.0L
  • V8
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
I am getting my oil pressure low warning on my display on my 2005 Chevy Silverado HD1500. I had it looked over by a friend, changed the oil. Seemed to go away. Now that it is getting cold, it's a daily occurrence. Once the truck warms up, It's fine, however I don't want to be running my engine with insufficient oil coverage.
What do you recommend? I have very little mechanical experience but also don't want to take it to a shop and get taken to town on my charges.
Is my oil pump shot? Any other things I can try to rule out before biting the bullet on a new oil pump?
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
The oil pump is the last thing to think about. First, have the oil pressure checked with a mechanical gauge to see if it really is low. If it's okay, suspect the sending unit. If the pressure is low, suspect worn bearings. The clue to worn bearings is the oil pressure will come back up when you raise engine speed a little. Typically a defective sending unit that's reading low will do it at any engine speed.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
CWALBY
  • MEMBER
Thanks for your timely response!
I am wondering what kind of bearings you are referring to? When I do increase the RPM's (whether in neutral or in drive), the oil pressure does increase - sometimes a little, sometimes a lot - again depending on engine temp (more if warm, less if cold).
And the warning message (and constant chiming) will remain until it reaches a sufficient pressure (approx. 135 kPa/20 psi).
Thanks again for your help!
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
The bearings are thin curved strips of metal that sit between the crankshaft "journals" and the connecting rods, and between the engine block and crankshaft. They usually have three layers of metal. The first layer is real soft so dirt and grit embed in it rather than going around and scratching the polished surface of the crankshaft journals. The next layers are harder to absorb impact.

The gap, or "clearance" between a bearing and the metal part riding on it is very tight; in the order of.005". Oil is forced into that gap under pressure to isolate the moving parts from each other. That oil oozes out the sides, then falls back into the oil pan or gets whipped around to coat other areas, namely the cylinder walls.

The oil pressure is maintained because it's hard to push the oil through the tight clearances. Anything that makes it easier for the oil to run out will result in lower pressure. Oil gets thinner when it gets warm. That lets it run out faster, so the volume being pumped has to increase. Most oil pumps have no problem pumping enough volume, but with low pressure, those moving metal parts can start to make contact. The soft first layer of metal begins to rub off of the bearings. You can actually see that as a significantly discolored area. The missing metal results in increased clearance so the oil can run out even easier and will be less effective at isolating the moving parts. Once that wear starts, it accelerates real fast until you hear a knocking noise from the parts banging against each other.

If this is caught early enough, sometimes new bearings can be installed and the wear stops taking place. That has to be done before the journals becomes scored or scratched. Any roughness on a journal will tear up the new bearing. For a V-8 engine, the crankshaft sits on five bearings, and there's eight connecting rod bearings. It only takes one of them to be worn to allow the oil to run out too fast and cause low pressure.

Depending on the engine design, there are usually five or six camshaft bearings too. Those get oil in such a way that there's not much pressure left. They don't have to handle the same pounding forces as the other bearings so they rarely cause a problem.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
TXHOTROD
  • MEMBER
  • 2005 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 86,000 MILES
Installed a new cam in the motor, after initial startup there was no oil pressure registered on the gauge. We replaced the oil pump with a brand new Melling unit. Reassembled engine and tried again, this time disabled the starting system and just cranked it. No pressure registered on the guage. Pulled valve covers to verify and there is no oil pumping up pushrods. I am stumped, has anybody got any ideas? Do you prime the pump, if how? Any resoponse will be appreciated.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
BUZZSAW
  • EXPERT
Whats your engine size? 4.8 or a 5.3, also to make sure Im looking at the right picture is the oil pump mounted to the crankshaft
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
CWALBY
  • MEMBER
Thanks again.
So get it on a mechanical gauge, and see if oil pressure is actually low. If not, then it's likely the sending unit. If oil pressure is low, likely the bearings? Which would be a pretty costly repair, correct? Fingers crossed it's the sending unit?
Sorry for the constant replies, as I mentioned I'm not mechanically inclined!
Thanks again. Very appreciated!
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
TXHOTROD
  • MEMBER
It is a 5.3 and yes the oil pump is on the front of the motor, being turned by the crankshaft.

Whats your engine size? 4.8 or a 5.3, also to make sure Im looking at the right picture is the oil pump mounted to the crankshaft[/quote:e8cec071ef]
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
Yup. You got it right. For Ford products replacing the bearings is a major job because the engine has to be lifted to get the oil pan off. For yours, and most other brands replacing bearings can often be done in half a day. Once it gets bad enough that the crankshaft is damaged, the engine has to be removed, and the job is sufficiently involved that you might as well do a total rebuild.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
BUZZSAW
  • EXPERT
Whats your engine size? 4.8 or a 5.3, also to make sure Im looking at the right picture is the oil pump mounted to the crankshaft[/quote:53e4c893e5][/quote:53e4c893e5]

yes you do have to prime it, you fill it full of oil and then use clean fresh white lithium grease to keep it in there( cover the holes with it )
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
TXHOTROD
  • MEMBER
So you are saying to plug up the outlet hole by the pressure relief valve with grease, fill up the pump then do the same to the inlet and install the pump? Correct?
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
AUDAVIS85
  • MEMBER
  • 2004 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 79,128 MILES
OKay so I was driving after a 120 mile trip about 2 miles from home and started to get some valve chatter when I got home I parked it and the next morning I fired the truck up and it said low oil pressure I checked the oil and some had scored on the stick. I am not getting ANY oil pressure. DO you think it is the pump? The Motor is a 4.8
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
DENNYP
  • EXPERT
Make sure the oil level is full. Check the oil pressure with a test gauge. If there is no pressure, replace the oil pump. If the pressure is good then goes away, check the main and rod and cam bearings. You could also check the seal on the oil pickup tube. Make sure it isn't damaged.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
BUZZSAW
  • EXPERT
Yes with white lithium grease in a tub then install it, before putting everything back together see if you have pressure(turn it over), make sure the crank is turning, make sure the key is in the crank for the oil pump flange that goes into the pump off the crank
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
TXHOTROD
  • MEMBER
It worked! Put it back together and it immediately picked up oil pressure upon starting. Thanks!
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
HUMBERTO PONCE
  • MEMBER
  • 2004 CHEVROLET SILVERADO
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 140,008 MILES
The low oil pressure indicator comes on but I check the oil and it's fine do you know what the problem could be on a 2004 chevy silverado?
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
RASMATAZ
  • EXPERT
Check the oil pressure with a mechanical gauge, if normal replace the oil pressure switch. If abnormal could mean oil pump and/or engine bearing.
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
SILVERADO SS
  • MEMBER
  • 2004 CHEVROLET SILVERADO
  • V8
  • AWD
  • AUTOMATIC
  • 120,000 MILES
04 silverado ss 6.0L did a oil change Mobil 1 and filter. Week later started up and no oil pressure a little gas and it went up. Two days later nothing. Put new sending unit in and nothing. Put a mechanical gauge and still nothing. Pulled sending unit out and cut off fuel so don't kill motor and no oil came out of where sending unit sits.

Could it be oil pick up, Or maybe the oil pump?
Or somthing else?
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)
Tiny
RASMATAZ
  • EXPERT
Could be the pick-up or the pump itself
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Thursday, September 3rd, 2020 AT 11:21 AM (Merged)

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