Accordinglytuned

This has happened to me as well, I still find it hilarious that this is a common issue for our cars lol.

It's right on top of the transmission wedged in there but no where for it to fall out, you'll have to look from above down or go from the bottom and try to push it up!

Chuck S

Fit a new gasket periodically. These turn to solid plastic fairly easily and once they become hard you need vice grips to tighten enough they won't fall off.

-- Chuck

Slowcrash_101

When the oil cap gasket goes bad you get a slight vacuum leak.

Car Analogy

Hint. A fresh o-ring will make the cap much less likely to back out. You can buy the o-ring cheap from Honda.

zeroptzero

The oem cap gasket has a raised ridge on it that squeezes tight when compressed and provides resistance to keep the cap tight. Over time the ridge wears flat and no longer produces tension on the cap, so it can come loose in some instances.

If your cap bottoms out without resistance when you spin it on during installation it likely no longer has the gasket ridge working properly. The cap should stop turning before it bottoms out, the final fraction of the last turn is what keeps the cap tight as the gasket ridge compresses..

Mitchelperkins

I spent a couple hours going through the transmission from top to bottom again to no avail. The spot that was commonly mentioned had nothing, is there a deeper crevice on top it might’ve gotten stuck in?

Slowcrash_101

Go for a drive and find some sharp right turns you can take safely. That will move the cap to the common location.

zeroptzero

maybe have someone rev the motor while you try and find the cap if you can reproduce the rattle sound. If not then the cap might be gone ?

Mitchelperkins

I did exactly this and that is my conclusion, in my situation the cap seems to have found its’ own way out. When my passenger held his hands on the center of the dash, the rattle could not be reproduced at any RPM. I know there are some methods of tightening up the dash, isn’t there a way to access bolts from the side?

zeroptzero

The dash does bolt from the two sides, but not likely to fix the source of the vibration. There can be sources of vibrations behind from loose screws, broken clips, and wiring. Mostly around the venting system, instrument cluster, behind the radio center cluster, and the passenger side of the dash. Worth a look if you can get behind there.