I have a noise that this engine has had as long as I can remember but have only had it after 100k miles. It almost sounds like the old GM Iron Duke 2.5L 4 cylinder with the Phenolic timing Gear and steel crank gear. They would knock at idle and light load.


This 2.4 has the same type of knock that I can only hear inside and under very light to no load in first and second around 3000 rpm. If any load or even cam timing comes in it gets softer or goes away. I can't hear it under the hood with the rest of the noise or even with a stethoscope.


I am guessing worn timing chain / guides but the rhythmic light knock is strange. Is this one of the 2.4's common high mileage noises?

 

in all the cobalts I've owned, knocking was never present in any of them.

 

Have you had any Auto's

 

ah thats a good point. all 4 of mine were Manuals.

 

Although it is an auto, I feel the noise is engine related. Much quieter when the oil is cool and a little thicker... Mobile 1, 5-30. Don't these have timing chain and guide or pin issues that can cause a rattle ?

 

Some of them had issues with faulty timing chain tensioners though I'm not sure what year they started using the "upgraded" design. Supposedly my car (2006) used to have the "faulty" timing chain tensioner though it never gave me any problems up to 100,000 miles. It's really pretty easy to change out though if that is your issue.

 

usually that is a rattle noise on cold startup. not when the car is running though.

 

I guess I will find it eventually. I will build a new one first then go through this one later.

 

piston slap maybe?

 

I gave that some thought but from my experience in diagnosing and building engines, they slap when cold and quiet down after expanding. This is just the opposite

 

sounds almost like the beginning of rod knock then.

 

Been doing it as long as I can remember and the way it has been ran I don't know how it could go this long.