2005 Chevrolet Silverado "Oil Pressure Low" warning daily.

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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Friday, November 27th, 2015 AT 8:41 AM

5 Replies

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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Friday, November 27th, 2015 AT 8:58 AM
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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Friday, November 27th, 2015 AT 9:42 AM
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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Friday, November 27th, 2015 AT 10:17 AM
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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Friday, November 27th, 2015 AT 10:38 AM
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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Friday, November 27th, 2015 AT 12:03 PM

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