'03 GMC 4.8L ENGINE TAP

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blondie

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I have an '03 GMC Sierra 4.8l with 43k miles that can only be described as a tap in the engine at idle. It is the most obvious when it's warmed up and will go away if you increase the rpm to around a 1000.

I've been told various things...from it's a normal characteristic....piston slap....lifters...to I need to use 10W40 oil or even a synthetic.

The book calls for 10W30 which is all I've ever used in it. The oil has been changed every 3k or less. This truck has been well taken care of. I've listened to other 4.8l, 5.3l and 6.0l and haven't found any that sounds like mine. Any idea what it could be and what to do if anything to correct?
 
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blondie!!
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I have a '03 GMC Sierra 5.3L.

Piston slap usually is during a cold engine. Could be lifters.

Has the engine been run low on oil?

What oil filters have been in it?
 
Welcome to the forum Blondie, i sincerely doubt its normal or piston slap, depending on how handy you are, you can buy a mechanic's stethoscope.

Its a device used to pin point noises, looks very similar to what dr's use. Another way to do this is to use a long screw driver and place it against various parts of the engine, placing one end on the engine and one end to your ear. Move it around till you narrow down the area the noise is coming from.

Good luck and do let us know what you find out
 
Never been run low. AC Delco filters from the dealership. Never been run hard. Very well taken care of.
 
Originally Posted By: blondie
Never been run low. AC Delco filters from the dealership. Never been run hard. Very well taken care of.


Ok...

Do you have an oil gauge?

If so, where does it sit at at an idle when warm?

Mine sits at 38-40 at an idle.
 
Could be a broken bolt or crack in the exhaust manifold. That is why it gets worse when hot. The manifold expands when heated up. This has been a problem in these trucks from time to time.
 
Yes, I do have an oil gauge and it stays right around 40 as well. Littl less at idle and a little more on the road.
 
Originally Posted By: blondie
Yes, I do have an oil gauge and it stays right around 40 as well. Littl less at idle and a little more on the road.


Ok, that's good to know.....

Now, I'm leaning towards what e.t.p mentioned...
 
I have the same thing in my 04 5.3L v8. I think it is lifter tick. Lifters on this engine are known to collapse.

Mine goes away after driving for about 3 minutes. It comes back when I start up the engine again. Seemed to happen after some heavy towing at high rpms.

It probably happened around 65k miles on mine. I'm not worried about it.
 
Originally Posted By: blondie
This truck has done this from the start.


Has the Dealer seen it for this reason? Do they know of it if and when they change the oil?
 
Originally Posted By: endeavor to persevere
Could be a broken bolt or crack in the exhaust manifold. That is why it gets worse when hot. The manifold expands when heated up. This has been a problem in these trucks from time to time.


Could be even easier than that, like on my previous '98 chev k1500. Very easy fix. There is an asbestos donut that seals the exhaust manifold to the exhaust pipe right at the connection. Mine blew a hole through the donut.

A little penetrating oil and two nuts to remove gets to the donut. Most auto parts places sell them cheaply. It would be easier to get it at the dealer to make sure you get the right one. My independent auto parts place got it wrong the first time. I recall it costing 13 dollars or so.
 
The second video is very helpful. Sounds exactly the way my exhaust leak sounded.

First one sounds significantly louder than the sound my engine makes.

Only making these observations to help the original poster, since the OP's engine is basically identical to mine.
 
Definitely not the whooshy sound. More like the first but not exactly. Without the tap it would be perfectly smooth and quiet.

I actually work at a dealership...but I don't think they take me seriously....could it be because I'm a female? Seriously, they know I'm not mechanically stupid...I actually want to be aware of any info I can get myself.

Excuse me if I bow out for a few....I have to sign a deal up. Please continue though. I really appreciate the help.
 
Well, geez, smack them up!
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Have them evaluate it for real and go from there. It just may be something rattling in the exhaust or the donut.
 
Yeah, well great idea....why didn't I think of that.

Where do you think I got the responses I did? Don't you recognize typical dealership responses for issues they don't want to address? Which is what led me here.

Thanks for your time. I will inquire about the items you suggested.
 
Kinda wondered......

If it's the donut, you can now say you know a hole can be in a donut and not let them think they can confuse you. Ha!
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