1999 SS

iTrader: (3)

my 00 TA has piston slap pretty bad and about a weak ago i changed my oil to straight nonsynthetic 40 weight and the noise is about 90%+ gone.

ls1wfo

yeah, seems like I read somewhere that if you have really bad slap to change to castrol 10W40 & it would completely eliminate it.

BJM

iTrader: (1)

The higher viscosity oil has a lot more drag on the con rod bearings so the piston is planted against the cylinder wall more firmly, quieting the slap. Be careful revving when cold in cold weather, the oil pump loads will be a lot higher and the oil will struggle to get everywhere through the engine until it warms up.

PREDATOR-Z

I run 40 weight in all my LS motors (Mobil1-0W40)

black01_WS6

iTrader: (13)

I am running the Royal Purple 10W40 and am not burning as much oil, and pressure is up, and it seems like the car is runnign better than running the 0W40 Mobil 1. I also have 99,xxx miles.

SSDude

M1 0w-40 will shear down to a 30wt by design with 2,000 miles of usage. It does not thicken back up to a 40wt until after about 10,000 miles.

PREDATOR-Z

In all the years I've used it, I never had any lubrication issues or lifter issues. Oil pressure is always within parameters.
On my new built BTW, it is the first time I use a ported pump. All my other motors just ran LS6 stock pumps with no issues.
My cylinder hones have always been in top shape, cam lobe wear etc....
In my environment, it works well as per my experience.

SSDude

Without a doubt the M1 5w-40 is a better oil. It is more shear stable and contain 25% ester. It cost the same as the 0w-40 and is bullet proof.

RevGTO

iTrader: (12)

He said "straight non-synthetic 40W." I take that to mean non-multigrade SAE 40W. That's wildly heavy oil to run in an LS1.