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Normal Engine Noise?

18K views 17 replies 8 participants last post by  Falcon LS 
#1 ·
GM did their homework. I think the 4.2L I-6 is a good match for the Trailblazer/Envoy – plenty of pep with acceptable fuel consumption. One of the first things I noticed on the test drive was the powerful but yet smooth and quiet engine – even at idle. I was impressed. Despite this, it was shortly after my purchase when I noticed an engine noise. I’m not sure what it is. I’m not familiar with the engine design of the 4.2L I-6 as I have mainly been around OHV (pushrod type) engines, but it sounds like a slight taping or ticking noise coming from the engine. The sound is not very loud so it’s not immediately noticeable; although, it does seem to be most noticeable during warm up, but once the engine reaches operating temperature the sound becomes almost undetectable. Call me crazy, but during the first couple minutes of driving it almost sounds like a (very quiet) diesel engine – best way I can describe it. Can anyone tell me the exact source and cause of this particular noise? Has anyone else noticed a similar noise? Is this considered “normal?” Fluid levels are good. Dealer performed an oil/filter change just before I took delivery. Should I be concerned?
 
#2 ·
sounds like 2 possible causes.......
a cold Inline 6 may produce the ticking/knocking sound when cold.
it may be related to piston slap......... the other is Cold carbon knock.
I get cold carbon knock after lets say maybe 10,000 miles of use or so......
this can be quieted down by running a bottle of techron to get rid of that carbon build up. It helps mine quiet down.

Once the engine is warm- the I6 purrs and makes very little noise.
 
#3 ·
Most likely it is the fan clutch. The design (up until about '07 models) had a system for opening and closing a valve to allow the silicone based fluid to move around. The ticking is the valve opening & closing when cold.

As you noticed, it goes away when the engine warms up.
 
#5 ·
My 02 does the noise thing on cold start. It is piston slap and goes away when there is heat in the motor. The ticking noise is most likely the fan clutch. Start the engine cold and open the hood. Listen for the ticking. Looking from the front, there is a weathertight plug on the right side of the fan housing cowl. Unplug it and the ticking should stop. BE CAREFUL, the fan is very close to the plug. Mine started ticking 6 months before the fan clutch died.
 
#6 ·
the ticking fan clutch and the piston slap or cold carbon knock are different tick sounds.

the fan clutch- you can leave the hood closed and crouch next to the front drivers wheelwell area... and you will hear a very distinct ticking sound-

the piston slap can be heard inside the vehicle- while the fan clutch- I have to open window or door and listen carefully....

hope that helps
 
#7 ·
Well I can definitely hear the noise I described from inside the vehicle – doors and windows closed. Is this a bad thing? Piston slap doesn’t sound like a good thing! Should I take my Trailblazer to the dealership? What should I tell them?
 
#8 ·
in severe cases- the V8's had some work done on them.
but I have never heard of a I6 being repaired for piston slap.
they will most likely tell you its normal.
Many post on other websites say its not going to damage the engine.
 
#9 ·
Ok. What exactly is piston slap? What causes this to happen? Is it just simply a design flaw? Will this cause any type of reliability issues later down the road?

Also, what is carbon knock?

Thanks.
 
#10 ·
piston slap in short is caused by a piston that doesnt exactly fit in the combustion chamber. so it rattles and knocks as it moves up and down. as it heats up and expands and the movement stops.

cold carbon knock is built up carbon on the piston....


carbon buildup- in older cars- would cause run on. meaning that when the engine was turned off....there was enough HOT carbon in the piston to continues to ignite fuel and the engine would run on... and then sputter to a stop...

cold carbon knock- - I cant find a definition of it at the moment....
 
#11 ·
I’m still a little confused… should I really have these issues with fewer than 34,000 miles on the 4.2L I-6? My Trailblazer is still covered under GM’s 5-year/100,000 mile powertrain warranty.
 
#13 ·
All vehicles have issues.....some are there when you drive off the lot, opthers happen later. If in doubt, take it into the dealer and complain:hissy:.
 
#14 ·
the carbon knock can really pop its head up if you use cheap gas.
using gas with say techron keeps it cleaner.
Have you tried using a bottle of techron concentrate to see if it quiets down a bit?
I know mine does......
 
#15 ·
Engine Noise

Hello all, my 1st post, after many years of wanting the XUV I decided to purchase. I bought the truck from a well to do old retired guy. I actually flew 800 miles to purchase the truck after seeing about 100 photos. I drove it home and it ran like a dream and was getting around 22 mpg going 75 to 80 the entire trip home.

The previous owned had never had the truck over 65 mph and by the smell of it after getting on it I blew out alot of crap that was built up. Got the truck home and changed the fluids with syn oil, plugs AC delco, fuel filter, Airad cold air cleaner, Techtron fuel cleaner with a full tank of 93 octane, tension pully, wheel bearings, shocks and brakes all around, stabilizers all around and a new battery.

My issue now is I get the dieselly for the 1st 5 minutes until warm, and when the truck accelerates and the tach goes between 2 and 4 i hear what sounds like a timing chain rattle. My mechanic says he can barely hear it and not to worry about because once it warms up it runs sweet, but i still hear the noise. Its not the fan or a lose sheild, any suggestions?
 
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