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2007 GMC Sierra loud tapping from engine

Tiny
CARTER96
  • MEMBER
  • 2007 GMC SIERRA
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
Last week my info center in my truck started giving me a low oil level warning. I checked the oil and it was full so I thought it was a bad warning. My old silverado did that all the time. Last night I started my truck and the tapping started but quit within seconds. I got worried and checked my oil again and it was fine so I decided to change it even though I didn't have even 2000 miles since last change. The oil had a good bit of sludge in it which really worries me because I have been loosing a little coolant. I changed it and refilled then started my truck and the tapping was 10x worse and it doesn't stop. My oil pressure gauge is very erratic going up and down 20 psi. I did a compression gas test on my coolant reservoir and the fluid in the tester didn't turn blue. I have noticed a loss of power lately also. I am worried the engine is shot and I cant bring it to anyone till Monday so I was just hoping for some ideas of things I can check myself before I bring it to the shop. I am not a mechanic but I can do enough to get into trouble. Thanks in advance for the help
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Saturday, April 5th, 2014 AT 11:11 AM

7 Replies

Tiny
CARTER96
  • MEMBER
  • 17 POSTS
That was supposed to say combustion gas test not compression
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Saturday, April 5th, 2014 AT 12:45 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The first thing I would do is check the actual oil pressure with a gauge to see if its low. That would be my starting point.
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Saturday, April 5th, 2014 AT 2:50 PM
Tiny
CARTER96
  • MEMBER
  • 17 POSTS
I have never done that before. How would I go about testing the oil pressure?
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Saturday, April 5th, 2014 AT 2:56 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
You would unscrew the oil sending and hook the oil pressure gauge up it where the sending unit goes. With engine hot at 1,000 rpms min pressure 6 psi at 2,000 rpms 18psi at 4,000 rpms 24psi min. The sending unit is top rear of engine.
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Saturday, April 5th, 2014 AT 8:15 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
It sounds like the oil pump pick up might be plugged from the sludge in the motor. I know its difficult to check this problem, but I've seen tis problem before in other engines. Please let me know what happens, thanks for using 2carpros. Com.

Best, Ken
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Saturday, April 5th, 2014 AT 9:42 PM
Tiny
CARTER96
  • MEMBER
  • 17 POSTS
The sludge is another thing. What are the common causes of that. I am very religious about changing my oil on time and I have used nothing but castrol syntec and mobil 1 filters or bosch depending on which they have in stock at the time. I put about 30000 miles a year on my truck but almost all those are hwy miles with little towing.
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Sunday, April 6th, 2014 AT 9:51 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Have you owned the truck since it was new? If so, I would change motor oil type to Valvoline after the repair.

Saturntech9 is right though, try installing a manual gauge to see if the sludge is a problem. If so you might have to bite the bullet and remove the oil pan.

Best, Ken
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Sunday, April 6th, 2014 AT 11:14 AM

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