Engine knock in 2002 Suburban

[rboit]

I have a 2002 Suburban, 5.3 L with 80,000 miles. About half the time I start the vehicle there is a loud knock that lasts about 30 seconds, then quits as the engine warms. This is a family vehicle that I've owned since it was new and it has been treated very well, with oil changes every 3-5K. Any ideas on what could be causing the knock before I take it to the dealer for a diagnosis?

Thanks

[derekbitt]

from what i know this is a common problem, you will read many compliants about these motors. Chevy does have a program about these motors but they dont advertise it or offer it, you will really have to go after them to get them to do something about it.. if you take it to the dealer they will tell you that nothing is wrong with the engine and the knock will not cause any problems. the word is that combustion chamber gets carbon deposits and these deposits soften as the engine warms and the knockn quits. I have read that chevy bought some vehicles back from customers but not after a huge fight from the customer. if you have the 100k warranty you better get after this befor it expires. Good Luck. just remember your 40,000$ truck should make these noises when the dealer tells you nothing is wrong. I love chevy trucks but this crap is why i bought my wife a Toyota sequoia. sorry to be so negative.

[idmetro]

If carbon deposits are the culprit you might be able to lessen them by using a product called Seafoam. With the engine idling you trickle about 1/3 of a can into the brake booster line (so it will get sucked into the intake) then literally dump it in to the point the engine dies (you'll use 1/2 a can or so here) let the engine sit 15 minutes or so reconnect the brake booster line then fire it back up. Pour the reamining Seafoam in the gas tank. It will be tough to start but it will start and then the smoking will begin. It will smoke so much it'll make you think you have a serious internal problem, let the truck warm up a bit and take it for a spin; initially it will sputter and cough but as it runs it will smooth out; in another 15 minutes or so the smoking will go away and I think you will notice a difference. Seafoam is available around here at Napa and Schucks. If you don't like it you're out less than $10....

[rboit]

Thanks. I am a big fan of Seafoam, and have used it in my Suburban (and everything else I own). Unfortunately, it did not stop the knock.

[rboit]

Thanks. This is my 3rd Suburban and I've always considered them to be great vehicles. But to have an engine knocking at 80,000 miles for all the money I spent is not right. The Sequoia will be my next vehicle as well.

[idmetro]

Sorry to hear that. I can understand the frustration as when you shell out serious $$$ for a vehicle it does not seem unreasonable to expect it to perform well. Which leaves us with the rhetorical question: Why is the response time from detroit ~5yrs longer to listen/respond to the consumer than that from Japan?

[maxwedge]

Lots of anecdotal comments/suggestions by all, no one who knows whats what has heard this, nor has any suggestion of the real problem been offered either by a dealer or indepedent or any warranty consideration or repair suggestion been offered or denied... Btw it took Toyota almost 3 model years to correct the ft brake issues on the Tundra.

[derekbitt]

there is a lot of anectodal evidence is because chevy, has not publically solved this problem and in recent years, as come out with vehicles that have not recieved the best reviews on their quality (look at any professional reviewer). It is sad that chevy has been building trucks for almost 100 years, and nissan has built a full size truck and in less than 5 yrs it is reviewed to be the best light duty full size truck. still love chevys though, ill keep putting new intake gasktes on them, replacing fuel pumps, dealing with mystery knocking (at 80k).

[GMMerlin]

The "knock" is caused by carbon deposits on the piston.
When the engine is cold, the carbon is hard..as the engine runs, the carbon absorbs the fuel and softens up..this is why the noise you hear usually starts after a few seconds of running and can last up to a minute.
Your dealer has a TSB and other published service information on how to deal with the concern.
I have a 02 GMC that has had this condition since 18000 miles and now has 98000 miles with no ill effects.
There are people out there that will tell you that this is called "piston slap".
These 2 noises are similar, but the effects are quite different.
Piston slap is caused by a slightly undersized piston that will create a knocking noise until it heats up and swells taking up the excess clearance.
Carbon knock is caused by a build up of carbon on the piston that will create a knocking noise that usually lasts 30 seconds.

[rboit]

Thanks for the info and comments. I like to gather a little advanced information and opinion before I go to my local Chevy dealer. I've had problems with my dealer before, so I like to go in armed with a little information beforehand.

[Habedere]

Kinda late to comment on this but I am a new-comer here. The engine on my '93 Suburban was rebuilt and after about 20,000 miles had a "cold knock." Not nice but decision time! I decided to install a "Master Lube" prelube system. Now just a flick of a switch for a couple of seconds, oil pressure climbs and the engine starts quietly. So far it works for some 40,000 miles. The thought is that I can transfer this investment onto another vehicle later. Tricky are the oil changes though because you have to drain the system with the solenoid and then you have to make sure that the little aluminum ball gets unseated when you put oil in the reservoir.

[Habedere]

Hi, well I have been trying to find out how to start a new thread, still don't know but here goes. I have another knock in my Suburban, but it comes from under the right side of the dash-board. It is what I think the mixer valve or gate in front of the fan motor. Question is: How hard is it to remove the fan motor? Is there a solenoid involved that is not quite closing etc? Does anyone have a likely name for the item to be replaced? Thanks