Cold start clack

[angrysnowplow]

Allrighty, the subject here is a 1998 one ton with a vortec 454 that only has around 45K on it.

Cold starts produce a clacking sound, that I had thought was piston slap, but now I hear that GM had problems with rod bearing clearances that year. The strange thing is, it does it most times, but not every time. The noise stops after less than a minute, and the truck runs and drives great once it's warmed up.

1. Would a high volume oil pump help matters at all? I don't think a pump that puts out a higher pressure would help, as now pressure at start-up is high, with the gauge almost pegged.

2. I have, in my quest to avoid having my motor self-destruct, come across a service bulletin for a PCM reflash that solves this problem in some cases. Has anybody heard of this, because having rod knock being fixed with a computer sounds too good to be true.

I appreciate any insight that anybody has...

 

[daleearnhardt01]

My 98 Z71 with a 350 with 50k miles does that too, sounds like piston slap to me but then again I had never heard of the bearing problem until now. Oil pressure is 60 at startup and stays around 50 while running then 40ish at idle when hot. Noise only happens on start-up and goes away after I rev it to get things circulating. Never see any metal in the oil and I run the piss out of this truck and Im not really worried about it. I attribute it to piston slap or just dry start-up...

 

[angrysnowplow]

ttt


All the tsb and hour of stealership labor did was plug the truck into a computer and lower the rpm 'flare' at start up. Helped slightly, could still hear the noise the 1st cold start after my appointment at the stealership.

The noise lasts much longer these days than even this past winter. And it's either my imagination, or the start up flare is back up again.

I am almost positive the intake is leaking, tell me that could be part of the problem.

 

[c_deezy]

I'd try putting some lucas oil stabilizer in it. That stuff is great and will help with cold start clack, at least it seemed to in my chevy. Helps to keep the oil from draining out of everything after it sits for awhile and prevents those first few seconds of low oil pressure at startup.

 

[perp]

i have heard that this noise is the injectors clicking when cold.........just what someone else said, i don't know myself

 

[thezentree]

I'd try putting some lucas oil stabilizer in it. That stuff is great and will help with cold start clack, at least it seemed to in my chevy. Helps to keep the oil from draining out of everything after it sits for awhile and prevents those first few seconds of low oil pressure at startup.

I used to run that stuff, and in my opinion, it worsened the cold start knock/clack in my 97. I used to swear by it, but I thought long and hard about it (there have been plenty of threads on the stuff in the past), and decided not to use it last oil change. Well, the oil pan leak disappeared and I gained about a mile per gallon, and my truck seems to run smoother, but that's the seat of the pants dyno speaking. If you think about it, it's sludge that you're adding to CLEAN oil, and while it might be slick, it's real thick, so it adds resistance to the motor, which you don't want. I also read an independent test on the stuff that showed that it foams at higher RPMs. Air pockets in a lubricant can't be good.

At any rate, it IS thicker than oil, and will thicken oil when it's still cold, so I'd imagine that the higher viscosity when cold would impede lubrication to the point that the Lucas stuff would make the problem worse. And after switching to straight Mobil 10W-30, my cold start knock is not nearly as bad.

c_deezy, I'm not saying you're wrong, just givin the guy another perspective on the stuff. angrysnowplow, do a search on Lucas oil stabilizer before you run it, learn somethin about it.