Losing oil

2010 NISSAN X-TRAIL
93,500 MILES • 2.5L • 4 CYL • 2WD • AUTOMATIC
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PORTGAS D ACE
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Hello, my car engine oil has decreased, and the fourth spark plug has oil on it. i tested it last year the mechanic told me that my engine has pressure. so, my question is, how i know if i have bad piston ring or damaged cylinder wall?? please i need a scientific answer. Thank you
Jan 18, 2022 at 11:58 AM
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SQM
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Hello,

One of the most common causes for having oil in the spark plug is having leaking spark plug tube seal or valve cover gasket.
If your compression is good, then the issue is not in the cylinder head.
Which leads to the valve cover gasket issue.

https://www.2carpros.com/articles/replace-valve-cover-gasket

I have attached the diagrams for a Frontier X-Trail 2.5L. If it is a different model X-trail let me know.
Any questions or concerns please feel free to ask.

Thank you.
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Jan 18, 2022 at 1:12 PM
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PORTGAS D ACE
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The valve cover gasket is new and the compression is normal.
Jan 19, 2022 at 12:59 PM
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SQM
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Well, as you know it is possible to have a pinched gasket or a cracked cover to have the leak.
Do you know if the spark plug tube seals were replaced?
Jan 19, 2022 at 1:02 PM
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PORTGAS D ACE
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Yes, all cylinder head parts are new. also, the gasket is new.
Jan 19, 2022 at 1:32 PM
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SQM
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Are you getting any smoke out of the tailpipe?
The oil in the spark plug, is it on the threads or was it on the hose itself?

If you have leaky piston rings you will get blue smoke out of the tailpipe, due to oil burning in the combustion chamber. This will foul the spark plug and it will be black due to oil soaking.
Jan 19, 2022 at 7:13 PM
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PORTGAS D ACE
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The oil in the spark plug went out of the coil, I mean it obvious when someone sees the engine and there is no noticeable smoke, but it has the smell of burning oil in the tailpipe.
Jan 21, 2022 at 12:08 PM
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SQM
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If there was a piston ring leak, you would have blue smoke out of the tailpipe, due to oil burning in the combustion chamber.

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust

Without looking at the vehicle, everything that you have described points to a leak in the spark plug tube seal or the valve cover gasket. This will have oil on the back of the plug and will be on the ignition coil.
Jan 21, 2022 at 12:24 PM