What is causing the plug on top of the oil intake to be blown out and make it sound like a loud exhaust
Pressure, check your PCV valve and other vacuum hoses, there might be a blockage.
like a valve seal ,short the plug on that cylinder it will be quiet at least
Are the valve covers leakin' and drippin' oil onto the exhaust manifold making this in effect a Smoke Factory?~
ummm, these appear to have threads....you mean to tell me the thing unscrewed itself...all the time? https://www.google.com/#q=2007+chrysler+pt+cruiser+oil+filler+cap
Sounds like a LOT of build up in that motor......under pressure...
Check exaust out put, the symptoms sound like a seriously restricted catalyst. If the exhaust can't go out the back where does it go? That's right the intake the pressure finds a weak spot and equals the barometric pressure thus the exaust sound. Disconnect exaust flange 2 13mm bolts they have a tab on the nut side. W exaust undone at manifold start and w brake set and all rev engine see if symptoms seem cured. You don't need to remove exhaust flange bolts completely as you need a lift to reinstall them if you take them out you'll see why. Let me know if that helps
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Kelly Little Ashford