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Dear advisor,

I have a 2001 Civic. The Nulon fully synthetic oil was changed 6.5 months ago (it was changed 7.5 months before that). The engine oil seems dirtier than usual, and it is also dirtier than the oil in my other car (at about the same oil change interval). The Civic is running well and normally, but could the dirtier oil indicate that its PCV valve or hose is blocked or starting to clog up? A Civic manual (Haynes) says the PCV hose can be pinched with pliers to see if the PCV valve makes a clicking sound to indicate that it is working properly. Would pinching the hose damage it, given that it may have become hardened and brittle with age?

Or could there be other causes of dirtier oil like a dirty air filter?

Many thanks for your expert advice.

Cheers.
Leo

We've discussed this with an industrial chemist at one of the major oil companies, and they believe this will be because the fully synthetic oil you are using is of a superior quality to that which you were using before, so is doing a much better job of cleaning your engine.
The new oil is likely to have a better performing detergent quality and possibly a higher API or ACEA rating to your old oil.
As the oil is designed to hold the soot/carbon in suspension, it has a much darker appearance. This will be especially so if the car has not had a thorough service history, and so may be a little carbonned up anyway (as is often the case with Japanese Imports).
Their thoughts are that you might be well advised to continue with running a quality fully synthetic, and regular changes, then eventually the oil may clean your engine to the point where it is no longer taking on this dark colour.
Essentially, what they're saying is that this oil is doing a better job to the oil you were using before. It's unlikely to be a PCV problem.