What Would YOU Do? Knock Knock; Waterfall

[Pekoe]

Here's the deal; Four months ago I bought a 1997 Silverado X-Cab Z-71 with 77K miles. It has run fine but in the last couple of moths has the following:

1) In cold temps (in VT winter around 0 deg.) the engine knocks for about 5 minutes. It definitely is a lower end sound. When cold, you hear the water rushing typical of air in the coolant system

I know about intake issues (seems dry - no obvious leaks). I have topped off the coolant while the truck is running. I'm concerned about taking it to dealer - they may say intake - $700 please. How long should I drive it like this? How much should I expect to pay for intake gaskets if that's the problem

2) Transmission clunk from 2nd to 3rd gear. Should it be repaired immediately? Causes?

These things are bugging me and I'm concerned I am in for big money repairs. No time or mechanical ability to do myself.

Thanks

Barry

[abaird]

I have heard others talk about the transmission clunk from 2nd to 3rd. My truck doesn't do it(that i've noticed) but they said it seemed to be normal.

I have noticed the water rushing sound when cold but I never knew it was a problem. On mine it sounds like it comes from the heater lines area.

Are you sure it is a definate knock because when mine would start cold it used to sound like hell too but at aournd 110,000 miles I switched to mobil 1 synthetic and it went away.

To me weverything you described sounded pretty normal unless I have a lot of problems I don't know about. However if someone else has any info I would like to hear it too.

[joe92k1500]

From what i know, that knock sound is piston slap. It is a well recorded GM problem. I am not positive of the years involved, but there is even a class action lawsuit against them. Piston slap can shorten engine life, but it is impossible to tell by how much. Installing a block heater will help the slap problem. Like abaird did, synthetic oil can help with piston slap, but usually does not eliminate it. It is usually the piston is too small and moves too much in the cylinder ( the knocking noise) , or the cylinder has become out of round. The only way to eliminate it is new pistons and check the cylinders for out of round. Try a block heater and synthetic oil and see if it gets any better.

[abaird]

I was looking around on the internet and I could only find mentions of piston slap being a problem on 1999-2003 vehicles.

[broughy84]

Your right, piston slap is in the gen 4 body style. That being said, I have a 96 (pictured below) That does EVERYTHING you listed. I hear the knock in the mornings, It sounds like hell, I ALWAYS let it warm for about 2-3 minutes, I have not seen a 95-98 that does not do this. (Faulty check valve in the oil pump) I just had the intake gaskets changed on my 96, $291.82. That was gaskets, labor, thermostat, dist cap, rotor, oil, filter, antifreeze, and coolant flush. The "waterfall" is an O-ring inside the heater hose, if you pull it out I was told the noise will go away, I have not done this though. The trans clunk is normal. Don't worry about it. It's more of an annoyance than a problem.

[clampjockey]

though your knock may be a piston slap, i'd be weary of your crank bearings. i've blown up a lot of chev engines, and 9 times out of 10, turning the mains on the #7 or 8 rod is the culprit. i've heard lots about piston slap, but was never lucky enough to have that problem. lol. i believe 1990 2.8mpfi engines were notorious for piston slap. anyways, if i were you, i'd hook up an oil pressure guage to the engine and read what you have for oil pressure at start-up, and at warm idling. if its low, you could have problems. if its got normal pressure at start-up (when knocking) i'd be more convinced that its a piston slap.

[Cadillakin'98]

The transmissin "clunk" you are talking about, is it maybe more of a "clink" when shifting?? My '98 will do this every now and them like when I get up on it. But, whenever I Cadillac it, I don't hear it. I haven't been too concerned with it but I bet it's the U-joints so just keep your ears on it. Thats all I do cause I know if I ever feel my truck jerk when I hear that "clink" (or "clunk") noise, that means them babies are 'bout to break! I have heard alot of these trucks make that noise when drivin it hard. As far as the piston slap thing, I have heard of it, but don't experience it in my truck.