Smoke coming out of oil fill port

With respect to measuring the health of the PCV system there appears to be a special vacuum gauge in a small pressure range capable of measuring the subtle vacuums expected in the crankcase. There's a youtube video demonstrating the unit in operation. The diagnostic part is Volvo P/N 9997226 and there's an associated article detailing the acceptable ranges...

Volvo Crankcase Testing

Here is a good procedure to help evaluate the overall health of your customer’s Volvo. Measure its crankcase pressure as part of your preliminary diagnosis. Volvo part number 9997226 is a manometer that will help facilitate the process.

Measure the pressure in the crankcase:

• With the engine at operating temperature
• With the engine at idle
• With the A/C off
• With all electrical accessories off

The battery and charging system must also be in good condition.

Remove the oil dipstick and connect the manometer to the dipstick tube. Read the gauge.

For 5 and 6 cylinder turbocharged cars the value for clean crankcase ventilation is -.2 kPa or lower. If the reading is between -.02 and 0.0 kPa or any positive value, the crankcase ventilation is partially or fully blocked.

For 6 Cylinder non turbocharged cars the manometer should read approximately 0.0kPa at hook-up. Lightly squeeze the hose between the “T” fitting and the intake hose using clamp pliers. Be cautious not to close the hose off completely because this will damage the manometer.

If negative pressure is observed on the nanometer the crankcase ventilation is clean.

The readings given above are for seal level operations, higher altitude will reduce the vacuum reading slightly.

As a comparison to standard vacuum/pressure gauges you'll find OTC 5613 Vacuum/Pressure Gauge Kit which is listed as

Dual scale gauge reads 0-30 in. Hg Vac [0-101.6 kPa] and 0-70 cm Hg also reads 0-15 psi and 0-100 kPa.

One fella even identifies the inability to use a standard vacuum gauge in this diagnosis Volvo Breather Box Tool

I Realized a regular vacuum gauge won't work, you need one that reads in 1/2 lbs and less!

That's because the gauge is reading kPa not bar so a range of -0.5 to 0.5 is very minute. 0.5 kPa only equals about 7/100 psi!

These gauges are pricey ($150+), but I may be able to find some kind of scientific instrument device that's just as well. I think you can do a homemade water manometer too but I'll have to research vacuum capabilities.

I also found a pretty good article on the relation of burning oil and a clogged PCV system, but unfortunately he doesn't mention what sort of oil burn rate to expect nor anything about the sort of smoke we're seeing.

Volvo: Sometimes You Learn the Hard Way: Fixing Volvo Oil Leaks Right the First Time

Here's a relevant excerpt from the article...

Volvo has a couple of TSBs on diagnosing and cleaning some of the crankcase ventilation systems on newer s60, s70 and s80 cars. Its special tool, P/N 9997226, is attached to the dipstick tube and at idle they want to see -0.2 KPA or less. ... On a good car, even when raising the idle, the gauge won’t move above 0 psi. Plugged boxes are easy to see. We’ve seen more than 4 psi on some cars, and a psi of 0.5 on others. Remember that even if we see no pressure, the box can be partially plugged and should be replaced.

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Update 3/11/2018 Crankcase Pressure Measured High According to Water Manometer

I built a small water manometer from some aquarium airline hosing and filled it with an incredibly small amount of water. I had a small syringe for filling ink jet printer cartridges that helped because the volume needed was so very little, probably on the order of 0.5mL or less. Using the hose like a straw invariably overfilled it, hard as I tried to gently do so. I had to inject the small volume of water and then lasso the hose folded in half so the U of the line would allow the water to settle into it. This got the bubbles out which is necessary for a manometer to function. However it was a challenge with my choice of tubing since the water surface tension to the inner wall of the tubing was very strong given the small volume of water and competed greatly gravity which would otherwise allow the water to settle to the bottom. I'd recommend a larger hose if you have one, and adding some dye to the water for contrast. I then set a plumbline with a thread and a random piece of metal for a weight to mark the direction of gravity in the images.

One end of the hose inserted to the dipstick tube and sealed around with putty while the opposite end is left open to the atmosphere. I stuck a piece of blue tape to where the water level came to rest with the engine off and setup a ruler to gauge my measurements from. I then snapped a photo with a tripod setup with the engine OFF, which has the water line high (and even with the other end of the tube's U loop), followed by a second photo with the engine ON where the waterline drops towards the end of the hose connected to the dipstick tube. This height difference is the vacuum the engine is pulling and thus my crankcase pressure. That it pulled towards the engine is sign a vacuum was present but I had to convert the inches of water to the corresponding kPA to ensure I was within the spec spelled out by the Volvo Crankcase Testing section above. The cutoff is 0.2kPa, which if you google search 0.2kpa to in water it will pull in the google converter and give you a value of 0.8 inch of water. With my engine it was approximately, and seemingly just under, 0.5 inch, telling me that my PCV system was likely partially clogged.