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sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 16364
Experience:  ASE Master and Advanced level certified. Factory trained with 14 years dealership experience
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GMC Yukon XL 1500 Denali: I have a 2006 GMC Yukon XL Denali

Resolved Question:

I have a 2006 GMC Yukon XL Denali with 180K miles and a temporary knocking problem. I crank car from cold start, drive 3 miles @ 45mph to the interstate (70mph) and about 2 miles later, it sounds like metal rattling in engine which soon grows very loud. 3-4 more miles later and dies down to where I can't hear it.

My GMC dealer is 7 miles away so whenever I get there, it's quiet as can be. They said I was low on oil and needed an oil change. Pleaes. :(

My Oil Express said that I'm going to need a new engine.

What I believe is the oil pressure guage (small oil can with a drop of oil) slow start to approach 40 (scale is 0-80) and when the engine noise stops, the guage drops too.

I have no idea what I'm talking about but it's like the engine is running without oil and the pressure builds to a point that it suddenly starts flowing / lubricating and things get quiet.

This is not a good noise and I want to find the source.
Submitted: 10 months ago.
Category: Car
Expert:  sprinkles08 replied 10 months ago.

Hello and welcome!

 

If oil pressure is in question then the first thing I would recommend is checking the pressure with a manual gauge, starting from a code start. The pressure gauge on the dash isn't usually that close of a representation of actual pressure, and there are always potential electrical problems that can affect the gauge.

 

If pressure is actually low when the noise is happening then you have a bad oil pump, restricted pickup screen, or possibly a drainback issue due to sludge buildup in the engine.

 

It almost sounds as if you're describing piston slap, which to a degree is normal. Piston slap happens when the pistons are a little small for the bores and they make noise as the skirts hit the cylinder walls when they change direction at the top of bottom of the cylinder. As the aluminum pistons heat up they will start to expand and the noise will start to subside. Piston slap isn't uncommon and can be considered normal to a degree, but if yours has suddenly gotten worse then you definitely have a problem.

sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 16364
Experience: ASE Master and Advanced level certified. Factory trained with 14 years dealership experience
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