Just wanted to see if this is normal or should I start to worry. When I first start the car and take off I can hear rattle sounds coming from the engine. This is under normal acceleration. I would never run it hard when cold for various reasons. But when it gets up to normal operating temp the rattle goes away. It doesn't sound like a rod knocking. Also a rod knocking would go on all the time. And my oil pressure runs about 18-20 indicated psi at idle at normal operating temps and around 38-40 psi anytime above idle. Like I said I'm just hoping this is maybe a lifter or valve clatter and not more serious. Let me know what u guys think. Btw. It has around 156000 miles. Not sure if any of the drivetrain has ever been replaced.

 

Is the oil clean, full, and the correct viscosity?

 

stock engine, or has it been rebuilt? Forged pistons rattle when cold.

have you cut an oil filter open to look for debris?

It sounds like you have not had the car long, what history do you have of the car?

Bob

 

Not sure if it has been rebuilt. Didn't get much history when I bought it. I got it from a car dealer that took it on trade. So he didn't know too much. Oil is at capacity and clean. As for viscosity im not sure. I plan on changing it this week. It was just changed when I bought it but I wanted to put what I usually run so I know for sure. I know it has a small oil leak but I haven't had it up to run it down yet but its not too bad. I figured I would try to track it down when I go to change the oil.

 

My sons 96 Z does the same thing i when you start the engine when it's cold. -- It sounds like a dull knock.

I think it's coming from the catalytic on the drivers side. Maybe the core is a little loose inside when it's cold and expands when hot.....

 

I thought this was normal for the hypereutectic pistons that are factory because of the different expansion rates for them vs the surrounding iron?

 

In theory, hypereutectic pistons expand less with temperature than forged aluminum, and can be fitted tighter. But, both the LT1 and the LS1 exhibit "piston slap" when cold. The LS1 seems to be worse than the LT1. My Formula had faint slap from the day I bought it new.

So much for the theory.

 

I had a friend listen to it and he said it was piston slap and that's why it goes away when its up to temperature. He said that with my oil pressure readings are great and shouldn't have nothing to worry about. Just to keep the maintenance up and don't run it too hard until it warms up.

 

After the car reaches operating temperature and you get down on the gas do you here the same noise could be spark knock ??
Any chance you can get a video up ??

 

No knock at all after its up to temp. Even at wot. But I will try and get a vid up in the next day or so.

 

Any change after oil change?

 

Piston slap. My 95 Z28 has done it since it was new, now has 280000 miles on it. Don't worry about it.

 

Didn't get a chance for the oil change yet. hopefully this week and I will repost results there after.