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Today driving to work I heard a loud bang from the engine. When I had a chance to pull over I did(which wasnt for a fair amount of time), and after opening the hood, I noticed that my Oil cap was off. Thankfully, it was just sitting next to the hood, so I retrieved it, but my concern is why this happened.

The only thing I know of is that I added some oil over the weekend, and I may have not put the cap back on very tight. A definite blonde moment, and the reason I think it might just have been this is because there was no damage to the thread on the engine or the cap. I screwed it back on , and its nice and snug right now.

Otherwise, this could have been caused by excessive pressure, so Im checking the PCV Valve and hoses tonight.

Im wondering if anyone here with more mechanical experience may have other ideas as to what happened, and also if theres anything else I should check. Im worried I may have damaged my engine driving with no cap on for about 20-25 minutes. My oil light didnt come on, and the dipstick showed low, but it was still at the bottom notch.

Hoping I got away with one here.

 
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I doubt that a lose cap will make a pop sound, it seems like a pressure issue to me.

 
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So what is the cause of excessive pressure? Is the PCV valve and hose the main culprit here, or should I be looking somewhere else as well?

 
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Just checked the PCV Valve, pinched it with the car idling and it clicked, so its working.

 
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Just checked the PCV Valve, pinched it with the car idling and it clicked, so its working.

 
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Same thing happened to me...i was like WTF!? of course oil spattered all over my hood and that side of the engine bay...i have no clue why it came off, and i've changed my oil like 10 times in this car..it has never happened before.

 
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How recently? Have you had any problems since?

 
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strange. just tighten it down next time. i cant imagine how it could pop off lol the threads are pretty thick. maybe the cap was just loose and hit the hood and thats the pop you heard. maybe it just um idk. lol

 
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Yeah, I really think this one is a "apply directly to forehead" kind of mistake. :P