Vortec v6 cold start knock

[ShopMonkey68]

I bought a 97 blazer to use as a daily driverand I have noticed now that it has finnally gotten cold out that the engine has a slight knock to it when I first start it in the morning. The knock lasts about 10-20 seconds before it goes away depending how cold it is. I have 50-60 psi oil pressure at start-up and it never drops below about 25 when its hot and idleing in gear. It\'s full of 5w-30 and the oil filter has a check valve. Is this possibly spark related? I know ther are many GM experts on this board. Thanks in advance

Chris

[jeremytkoontz]

nope, it\'s not fuel related, it\'s GM related. A lot of 4.3s and V-8s do it. Most people just learn to live with it. It is from oil settling down in the oil pan over night. I have seen some \"pre-oilers\" that are basically an electic oil pump that comes on when you turn on the key. I have never personally used one of these but they are supposed to eliminate cold start knock.

[Scotty_S-15]

My every-day \'94 1500 w/stock 350 did it since it was new. Doesn\'t always do it, depends on where the engine stopped, I think. It can knock BIG for only a second or two, diminishing as oil pressure builds. 110K miles and still knocking, no more, no less... Someday it\'s gotta spin that rod bearing, right?

......... I used to write it off as a piston slap.... but it sure sounds like a rod.

[spacecadet]

I have to agree, it doesn\'t sound right. You do have to remeber that if the vehicle sat then thers no oil pressure. Once it turns a bit it will push out the rest of the oil on the bearings. As it starts the space here the oil WAS will now be an air gap. Thus the space for the rod to slap and make noise.

It will onlky last a few seconds because the engine will build oil pressre. Once the pressure is great enogh it will surrond the beari g a then it s quite.

Space.

[DROPPEDATBIRTH]

I have a 96 1500 with a 4.3 and it does the same thing almost every day 148,000 (knock on wood) and still going

[FastBikesRule]

I have a 2000 S-10 4.3 with only 52k and it does it too. I take it as a normal noise.



I\'ve got a \'96 LT1 that does it.



I also have an \'89 S-15 with a 175k 4.3. Sounds like a helicopter when you start it.

Smokes and makes crazy noises, but still runs fine.

[nolongergreen]

i have a 2001 tahoe with the vortec 8 in it. It also does it. It really sucks because its loud enough that when i leave the neighborhood and go passed the first houses if my neighbors are outside they think my truck is about to lock up the motor. Its almost emabarassing. I cant believe chevy let it go like that. If i were my neighbor i wouldnt buy one. http://www.s10v8.com/images/smilies/icon_biggrin.gif

[rayL]

GM made a big deal out of this a few years ago as they had been experimenting with the thousands of motors that have been swapped under warranty. The northstar motors had a terrible problem with this and @9grand a piece warranty cost i guess they wanted to see what was really up. this is the bulletin that was released



Engine Knock on Cold Start

1999-2002 Chevrolet and GMC C/K Pickup and Utility Models



2002 Cadillac Escalade (2WD)



with 4.8L, 5.3L or 6.0L Engine (VINs V, T, Z, U -- RPOs LR4, LM7, L59, LQ4)



This bulletin is being revised to add an additional engine to the models section. Please discard Corporate Bulletin Number 01-06-01-028 (Section 06-Engine).

Some of the above vehicles may exhibit an engine knock noise that begins in the first 19,000-24,000 km (12,000-15,000 mi) of use. The knock noise is most often noticed during initial start-up and typically disappears within the first 5-30 seconds (may last longer in extreme cold temperatures). The noise is usually more noticeable on the initial start-up when the temperature is below 10°C (50°F) and may be more pronounced on the first cold start following a long trip.

This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion and the cylinder wall. GM Powertrain Engineering, and an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. THIS NOISE DOES NOT HAVE ANY EFFECT ON THE LONGEVITY OF ANY OF THE ENGINE COMPONENTS.

Important

At this time, attempts to repair this condition by replacing the engine assembly or pistons are not recommended.

Please share the information found in this bulletin with customers who inquire about this condition. In the event they have additional questions or concerns, please advise your Area Service Manager.