[CJ098756]

As the title states, the engine knocks and it doesn't always stay knocking. Usually it starts up fine and starts knocking within a few minutes, Then it will go away for a while, and then come back. It just comes and goes and doesn't make any sense to me. When the problem first developed if you turned the car off and then back on, the noise went away.. which made me think it was a sensor or computer issue. However now it does not go away when you restart it. I have attached a video because I am at a loss and I'm just hoping it doesn't need a rebuild of any kind.

Mystery 08 Cobalt Knock

youtube.com

 

[1966tbird]

It sounds to me as valve lifter clatter…yet I can’t say for certain.
It would help if all of the cars vitals were given at the same time,..,.year, mileage, prior repair history…..

Now let’s assume for now it is valve clatter. This could be due to cam chain issues. The year of your cobalt is important here because GM updated the cam chain tensioner mid year 2008. There are posts here with images on what to look for and other posts with detailed instructions on how to replace. @Oldslowandugly

now what oil are you using, what is the outside temp? With the lifter clatter changing with time, it leads me to believe oil pressure issues…..this to could lead to a bad cam chain tensioner, oill system loosing prime, or possibly too thick of oil for the temp.

 

[Oldslowandugly]

It sounds to me as valve lifter clatter…

I agree- not a knock. A bearing knock sounds like banging on hollow metal. This may be the tensioner but you would first need to rig up a real oil pressure gauge. I tap into the spot where the oil pressure sensor is just under the oil filter housing. These engines run over 80psi when cold, around 40psi when hot. Test first.

 

[CJ098756]

It sounds to me as valve lifter clatter…yet I can’t say for certain.
It would help if all of the cars vitals were given at the same time,..,.year, mileage, prior repair history…..

Now let’s assume for now it is valve clatter. This could be due to cam chain issues. The year of your cobalt is important here because GM updated the cam chain tensioner mid year 2008. There are posts here with images on what to look for and other posts with detailed instructions on how to replace. @Oldslowandugly

now what oil are you using, what is the outside temp? With the lifter clatter changing with time, it leads me to believe oil pressure issues…..this to could lead to a bad cam chain tensioner, oill system loosing prime, or possibly too thick of oil for the temp.

It sounds to me as valve lifter clatter…yet I can’t say for certain.
It would help if all of the cars vitals were given at the same time,..,.year, mileage, prior repair history…..

Now let’s assume for now it is valve clatter. This could be due to cam chain issues. The year of your cobalt is important here because GM updated the cam chain tensioner mid year 2008. There are posts here with images on what to look for and other posts with detailed instructions on how to replace. @Oldslowandugly

now what oil are you using, what is the outside temp? With the lifter clatter changing with time, it leads me to believe oil pressure issues…..this to could lead to a bad cam chain tensioner, oill system loosing prime, or possibly too thick of oil for the temp.

The door panel says it was manufactured on 06/08. The car has 128,XXX miles on it. Outside temp today was around 45 degrees. At 115k miles or so, I had the dealer I got the car from do the timing chain tensioner with a whole new chain set, new guides, heck even a water pump.. it was a whole kit. We also ordered a separate kit for balance shaft as well which was replaced because It was already being torn open, the car has been very good to me, and it didn't add a whole lot of labor to do it all at once. They called for all of this stuff to be replaced because of how loud the chain slapping had gotten, and because it still had the original timing chain tensioner and it was causing a loud rattle from oil starvation on startup. All of this stuff was done at once about 8-12 months ago. Car has had no issues and has started perfectly and ran with zero real clattering noises until about a week ago or so, and i've tried to just keep it parked so I don't blow it up. As for what oil I use, I have always used SuperTech Advanced Full Synthetic (I know its group 3 and not a true full synthetic, but its a good oil for the price.) Ive had the car for 3 years and always ran this oil, and I always change it every 3-5 thousand miles religiously. I also always use a fram XG9018 filter. Apologies for not posting enough information originally. @1966tbird

 

[Oldslowandugly]

I'm still not seeing oil pressure reported. And of course there is the urban legend that a FRAM oil filter will destroy your engine. I don't know if that is true but I only use the GM AC Delco filter. Since you did all that work it seems unlikely the tensioner is the problem.

 

[1966tbird]

Learn where the oil pressure sending unit is and install a tee fitting and get an oil pressure reading.

 

[CJ098756]

UPDATE: Firstly thank you guys very much for all your replies I appreciate you all @1966tbird and @Oldslowandugly. I forgot to mention that my oil pan had been bottomed out and cracked, so I replaced it. The replacement part used was a cheap $60 oil pan from RockAuto. The person that did it offered to pay for the cheapest pan since it was their fault. This was about 3 weeks ago. A week later it started that mystery knock. I had it towed up to the dealership I'd gotten the car from and immediately a senior tech asked about what happened to the original pan, so i explained. He said I should have gotten a factory pan. He said something about cheap pans can have manufacturing imperfections and these 2.2s are sensitive to windage tray issues? I'm not exactly sure what his explanation was about but I returned the pan I got from RockAuto and went to a pick and pull and got a factory pan for $75. I got it installed on my car and I have had ZERO knocking noises. Sounds like a good ol' Cobalt again. Don't really understand how an oil pan can make that kind of difference, but I'm glad nothing needed rebuilt.

 

[Oldslowandugly]

Well done. That is the problem with cheap replacement parts. They may be 'close' but never the same as OEM. Obviously there was something with not enough clearance. Good thing the pan is aluminum as the only thing down there that could have been tapping was a connecting rod or crankshaft counterweight. A poorly located baffle makes sense. When we got our '05 the pan was cracked in the front down low. I epoxied it and that lasted for a few years but eventually it leaked. I had 'heard things' about Cobalt pans so I tracked down a junkyard OEM pan on Fleabay. The place even hot tanked it before shipping. Who does that?!? Once replaced it has been no trouble at all. Glad you solved it!