Buick Century 3100 Knocking sound

[countryboy9799]

Hi, I just purchased a 2001 Buick Century with the 3100. It is supposed to be pretty common to have a knocking sound on a cold start up. From everything I have read it suggests it is caused by the pistons being to short and possibly carboned up causing piston slap. The noise is quite loud at first and after a few minutes goes away for the most.

The other day I was looking through the oil fill cap and could tell the noise was in sync with the valves. If it was piston slap wouldnt it be twice as fast as the valves?

If it is in the valve train what should I try doing? MMO or seafoam in the oil?
Maybe 0W30 oil or is this to thin?
Or 15W40?
It calls for 5W30 in winter and 10W30 in the summer.
Thanks

 

[addyguy]

I have no doubt this is good 'ole piston slap. got it in my Cavalier.

Thicker oil sometimes helps, not always. Try a 'high mileage' 10W-30 for the summer to see if it helps.

 

[countryboy9799]

I would have to think since its such a known problem that it is piston slap but wouldnt the sound be twice as fast as the valves?

 

[Robenstein]

It could be both. Even after replacing pistons in ours it still had noise. I good dose of MMO helped clean the gunk out of a sticky lifter. I had some free Risolone around and ran it for a full OCI afterward and it cleaned the rest of it out.

I would try some MMO with some good high mileage oil like Valvoline Max Life. I actually run 10w30 diesel oil in ours since its dirt cheap, robust,and good for cleaning. I pay less than 2.50 a quart for it when I buy it in two gallon jugs.

 

[Nick R]

Originally Posted By: addyguy
I have no doubt this is good 'ole piston slap. got it in my Cavalier.

Thicker oil sometimes helps, not always. Try a 'high mileage' 10W-30 for the summer to see if it helps.


I think our expedition might actually have a tiny bit of piston slap on Motorcraft 5W-20. It doesn't have it on the current fill of 76 5W-20 dino.

I don't have any piston slap with my cavalier, but when its cold it does sound like a diesel, or something at idle. Not piston slap though.