2012 Civic manual 26000 miles.

The car has gone 3 times in the shop about a "thunk" when starting from still. "Thunk" but it is more like creaking from the frond end really.

The dealer tech diagnosed something from the suspension tower.... the 1st time they "tightened" it... 2nd time they ordered some part and 3rd time they replaced.. whatever.

To my dismay the "thunk" is still present and I figured that I would ignore it until the lease is over next year (can't happen quick enough).

Then in the last week I did an oil change. When I removed the aluminum pan, a large bolt can down out of nowhere. It is a M10x40 with no sign of previous wear installation.

Unfortunately that "thunk" persists. I scrutinized all the engine bay (motor & transmission mounts, suspension) yet there are areas that I can't see.

Maybe Honda techs with experience may have an idea where a M10x40 could come from.

 

Front subframe to unibody. That's the only thing that'll use a bolt that big and it'll definitely make a thunk if it's not there. The fact that it was loose and now out is pretty terrible. I wouldn't drive that car until you figure this out, a loose subframe bolt can be catastrophic.