Rep Power: 0

I just installed a new muffler a few days ago after the old one rusted through and fell off. The car seemed to be running fine, no issues, until today when I was driving and heard a bang like a rock flew up and hit the undercarriage. The first thing I checked was to see if any of the bolts from the new muffler came loose or something, and everything seemed fine with the exhaust. I did, however notice oil EVERYWHERE. So I open up the hood and the oil cap was missing from the engine. I thought maybe I had forgotten to put it on but i noticed that the threaded part was still inside. I now realize that the bang I heard was the sound of the cap flying off. Any ideas on why this happened and what problem may need fixed to prevent it from happening again? I have a 2007 civic ex about 97xxx miles.

 
Rep Power: 518

Wow, have not heard of that one,
but I do know how much oil can be thrown out by the spinning timing chain.....so get a new cap right away.

Make every attempt to clean all that oil off, especially the rubber seals, and the one strip on the cowl panel at the rear edge of the hood.

I'd wonder if something got thrown off the timing chain (broken chain guide issue?) and punched through the cap.

Got any unusual noises while running?

When was the last oil change, or when was the last time someone would have had that oil cap off?

 
Rep Power: 0

After some research apparently this has happened before. Seems like it may be the PCV valve, so I'll get a new cap and change out that valve and see how it goes.

 
Rep Power: 308

I think those caps are known to do that on that generation. (for whatever reason)

 
Rep Power: 209

it would take some serious pressure to do this, unless the cap was damaged/cracked before hand, i am surprised you didnt pop a gasket and have oil pissing out there before this happened

 
Rep Power: 308

Those caps tend to get tight for some reason (saw it just the other day on my 2010) It had not been touched since my mechanic put it back last change, and he had to work to get it loose.