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Q: Engine oil cap popped out without a reason

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My car engine oil cap came out without any reason, we noticed when we are driving the vehicle got oil smell in the car so we got a doubt and we opened the car hood , we noticed oil cap came out and oil got spilled all over ..If we think mechanic has not closed the cap properly when we gave it fot got oil change but we gave it 1 month back , if tht would be the case I could have smelled it initially why we got the smell now while driving.

My car has 97000 miles.
My car has an automatic transmission.

Oil fill caps have very tight seals. They have to seal tightly because all of the crankcase vapors within the engine have to be confined and recycled through the positive crankcase ventilation (PCV) system. Consequently, the only way the oil fill cap can actually come off is if the cap was not properly tightened the last time it was removed.

It is not unusual for quick change oil facilities to leave the cap off. Indeed, sometimes they will even forget to put the new engine oil in, after draining the old out. So, it is definitely possible that the cap could have simply laid loose in the fill hole for some time until the motion of the car just finally dislodged it.

You didn’t notice the odor of oil vapors earlier because the cap, although not tight, was "mostly" blocking the fill hole and thus nothing could really spill out. You probably did not lose a large amount of oil, so just check the oil level on the dipstick currently and if slightly low, bring the level to the full mark. Check when cold, oil expands somewhat when heated.

For your next oil and filter change, consider YourMechanic, it’s not likely a certified professional from YourMechanic will leave your cap off because the idea is customer service not mass production in a huge, impersonal shop. Plus, the service will cost you much less.

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