Dash or firewall rattle 6.6L gasser at stoplights

[Pryme]

On 6/17/2025 at 5:20 PM, UWSkier said:

thread necro time.

 

This was it!  One GM couldn't spare a $0.001 locking washer on the left-most coolant bottle bolt and it'd worked itself loose.

Is this the bolt? Mine was loose also! Kept hearing  faint rattle sound and hopefully this was it. 
 

https://youtube.com/shorts/jzt3XyxN7oU?feature=shared

 

[Chuck FB]

3 hours ago, Pryme said:

Is this the bolt? Mine was loose also! Kept hearing  faint rattle sound and hopefully this was it. 
 

https://youtube.com/shorts/jzt3XyxN7oU?feature=shared

 

Out of curiosity I took a look at the bolts on my truck and they had very little tension on them to the plastic but they were actually just tight enough not to allow the plastic feet to move much. After I checked the tightness I backed them off and then pushed on the tank some towards the firewall and then snugged them both up. Indeed it does seem rather goofy that they use a grommet that just slides loosely over threads of a bolt that sticks out the firewall but would allow for easy installation of the container at the factory. I guess if one still had issues with that vibrating I think a nut could be spun onto the threads to put a little pressure on the grommet and therefore the plastic so it held it onto the firewall. 

[UWSkier]

On 7/10/2025 at 2:32 PM, Pryme said:

Is this the bolt? Mine was loose also! Kept hearing  faint rattle sound and hopefully this was it. 
 

https://youtube.com/shorts/jzt3XyxN7oU?feature=shared

 

Yes, it's that bolt.  I tightened mine like Chuck did too.  Pull the bottle up tight to the fender and crank that sucker down.  Sound gone.

[Pryme]

My rattle now appears to be gone. So it was that loose bolt up top securing the coolant reservoir. Thanks for the heads up guys. 

[Chuck FB]

No sure why I wasn't thinking of this the other day but if one felt the need to keep the firewall portion of the coolant bottle from moving up and down, either a thin walled rubber or vinyl hose could be slipped over the bolt threads so that rubber grommet was able to slide over or wraps of electrical tape on the bolt to a diameter that snugged it up.