Left oil cap off after change
 

Well I did a smart thing.

I changed my oil last night and forgot to put the oil filler cap back on.

During my commute this morning, I noticed that when I would clutch-in to upshift the engine emitted a loud whining sound (only in high rpm above 5500 or so). I could also feel a vibration in the pedals. Clutch-out and power on -> no noise or vibration at all.

When I arrived, I popped the hood and (amazingly) found the oil cap right where I left it on my brake/clutch fluid reservoir cover. Also, there wasn't a single drop of oil in the engine bay. I'm amazed that none shot out of there during my 2 high rpm trials. Oil level is the same -- a few mm below H mark.

After lunch, I tested it again (with the cap on this time :icon14:) and no more noises or vibration as expected.

So! Questions for you car gurus:
What caused the loud whining noise and vibration with the clutch out? Some kind of oil pressure imbalance when engine was allowed to spin down from high rpm? Could that have starved the engine of oil at all?

Thanks for any helpful opinions!

Not really sure what caused your problem, yeah, oil pressure being non esistant is a problem, but as long as there was oil circulating, you should be ok

You could make a case that the oil cap muffles some engine noise but the chances of any damage is little.

Your oil travels far down the block after filling. My main concern would be contaminants from driving without the cap but if you noticed it after one ride I'd think it was ok.

Positive crank case pressure.

sounds like a cool name for a band!:tup:

It's a sealed system, until this happens, lots more air getting into the system unmonitored,

Thanks for the feedback everyone.

I feel pretty certain that my Z is just fine. I'm just glad I caught it early. I had googled my issue a while back and found a guy that left his oil-cap off for an entire week-long road trip :ughdance: