GM Cold Start Knock Info

TxDoc · April 19, 2002

Basically:

1-GM is aware of it.

2-It is not causing damage.

3-no fix is coming in the soon to be released TSB.

From Truck Trend:

"There've been a lot of complaints about cold-start knock in the Vortec engine family and most General Motor's customers are getting incomplete answers at dealerships. We've spoken with Matt Kester, assistant manager with GM Powertrain Product Comunications, about this situation. He said General Motor's engineers ARE AWARE of the problem and are currently in a RESEARCH STAGE. The cold-start knock involves the 4.8L, 5.3L and 6.0L V-8s in all applicable GM cars and trucks from '99 to '02. They believe the CAUSE IS carbon buildup on the circumference of the piston ABOVE the top piston ring. This interference is affecting the dynamics of PISTON TRAVEL and therefore causing a knock. It seems the problem begins after the first 12,000 to 15,000 miles and the knock will last between five and 30 seconds in temperatures below 50 degrees after a cold startup. The noise also seems more pronounced AFTER long trips and at lower temperatures. The use of a top engine cleaner will give only TEMPORARY results, IF ANY, and a replacement engine without modifications would most likely develop similar symptoms. We were also told that a Technical Service Bulletin is in the process of publication, which should provide and explanation of the condition, BUT NOT A FIX, and that carbon deposits and associated knock ARE NOT CAUSING ANY STRUCTURAL DAMAGE TO THE ENGINE. So,for now, don't let it bother you. We'll give you further details when the TSB becomes available."

ll356 · April 19, 2002

Dont let GM fool you that they are in a research stage of trying to solve the knocking problem. They have had 4 years on 3 engine familys only to come up with carbon deposits. If any of the technicians on here have seen the pistons on these engines they will admit that there is NOT a bit of carbon at all on the pistons or rings. It is all totally dimensional between the hypereutic piston size & the bore tolerances. Thats why most of the engines do NOT knock & only about 15% do knock. As a technician & owner of one of these knockers for over a year & the battles I fought with GM it is a total cop out that the TSB covers GM by saying that knocking is NORMAL. Since the knocking in not emissions or safety related they do not have to recall these defective engines. Short skirted aluminum pistons in virtually all of todays engines expand & contract in the tight bore clearances in all temperatures & have to be designed with those temperature extremes in mind. Most will not knock. Its when you fall out of bore tolerance & piston dimension that the combination causes the knocking. I finally got my engine replaced when I threatened photographs & measurements in detail to GM through the arbritation process. Sorry for the length guys but my knocking got to sound like a diesel whether it was 19 or 90 degrees outside. Should be embarassing to GM, but they do not care.

lauriet1 · April 19, 2002

Still no mention of the 8.1's huh? Too bad, mine just started Cold Start Tick @ 18,400K - I was planning to take it in, but since they still haven't listed the 8.1....how far would I get with the dealer?

ll356 · April 19, 2002

I need to say something positive about the engine knocking situation. Since GM replaced the engine you have no idea what a joy it is just to get in & drive the truck without having to put up with the knocking & without having to offer excuses to friends, neighbors, relatives, co-workers & others who have heard the knocking. Even with my new engine there is NO guarentee that it will not knock after 20K miles. Just to get in the truck & turn the key & drive it without the knocking makes all the difference in the world. Thats the way they should sound.

TxDoc · April 20, 2002

Did your new engine have any modifications that made it different from your old engine?

TxDoc · April 25, 2002

checking back

SixGunner · April 25, 2002

So, can I assume that this problem would start within about 20000 miles? I have a 2000 with 27000 miles on it. It has the cold start "tick" but no knock that I can hear. It's going to the dealer tonight, along with a tape of the cold start noise. Hopefully it isn't anything or they will fix whatever it is. If it is a big problem, I might dump the truck, though what kind of truck I'd get in it's place I don't know since I don't like Ford or Dodge, and a friend of mine has a Tacoma that also has a cold-start noise. He has had some problems with the dealer fixing it (different dealer than he bought it from), but I think he's got it taken care of now.

SixGunner · April 26, 2002

Heard a new idea from my dealer - only use the oil filters with the check valve in them. Seems like it couldn't hurt. He said AC Delco filters have them, but I don't know which others do (if anyone else does I'd like to know). The service manager at the dealer I go to says he doesn't think the valve is a standard item in filters yet. Mine had a Napa on it last time, and it will be the last Napa filter I use until I figure out what other filters have the check valve. Hopefully Fram and Purolater both have them, since I prefer these brands of filters anyway.

Other recommendations are as follows:

Don't use synthetic oil. It's not necessary and won't help.

Don't use Slick-50. Something about trying to squeeze a liquid that thick through an oil passage scares me.

Don't panic about this. Use alcohol as necessary to prevent panic ;)

Another note to others with this problem - take it to the dealer and get them to verify it so that it is on record as a complaint. Could be useful later if this problem gets worse.

;)