: 91 Brougham 5.7 knock noise on cold startup

11-09-10, 01:35 PM
OK here's a situation I am hoping someone can shed some light on....

My 5.7 (1991) Brougham has 84,000 miles, the oil is fairly clean between oil changes, does not leak oil, does not burn oil, and the oil pressure is great. HOWEVER, since the weather has become colder (I live in PA) I've noticed the motor has a minor knocking sound when I start it in the mornings. It takes a couple seconds after start-up for the sound to occur, then it goes away as the motor warms up. I just bought it last summer, so it didn't do it in the warmer months. I believe the motor was cared for, so it would suprise me if problem is due to lack of maintenance.

Any ideas what this could be? Also - I'm running regular 5w-30 oil, and the oil level is good.

11-09-10, 02:22 PM
may be a dumb question but could it be an exhaust leak you're hearing? Would make sense that it only happens in cold because the metal has contracted?

11-09-10, 03:14 PM
It could be a bearing that is starting to go, or isn't get oiled sufficiently because of the cold. If you are due for an oil change, put 5w40 oil in and see if that makes the noise stop (running a higher weight for one oil change cycle won't have any detrimental effect on the engine). If the noise is more like a ticking sound, as opposed to a metal on metal banging, then it is valve noise, which usually happens on cold starts because it takes a few seconds for the oil to reach the heads.

11-09-10, 07:17 PM
It could also be piston slap. My old 1999 Z28 with the LS1 would do that on cold startup, would sound like a minor tick, almost like a diesel type of noise. My Brougham with the 350 like yours does the same thing. Its not as loud as that LS1, but is noticable from outside the car. If its just a faint noise, don't worry about it.

Here's a video of it:


11-10-10, 02:42 AM
Piston slap was a known problem for 350s back then. I think there was even a service bulletin for it at some point. If it's ticking an exhaust leak somewhere at the exhaust manifolds will cause that.

11-10-10, 09:23 AM
I'm thinking a lifter is ticking.

11-10-10, 12:57 PM
+1 piston slap.

11-10-10, 08:06 PM
Thanks for all the input.....I forgot to mention I changed the oil the other day...was running 10w-30 then I changed to 5w-30 and that seemed to help. It wasn't real loud to begin with, but still it worried me because I never had that experience before. Once its warmed up it goes away. So I guess its nothing to worry about....