Diagnosing oil consumption on Nissan VQ35DE (350z / G35)

I have a 2004 Infiniti G35 6MT coupe. Nissan VQ35DE engine with a bit over 156,000 KMs (about 96,000 miles). Since I bought it, I’ve noticed some oil consumption at a rate of about a litre every 4,000 KMs (about a quart every 2,400 miles). There’s no smoke of any kind from the exhaust or anywhere else, there are no puddles on the floor. I changed the PCV valve about 200KMs ago, that doesn’t seem to have made any difference.

I put in Mobil1 5w30 synthetic on the first change, changed to Castrol Edge 0w30 A3/B4 at my most recent OCI (supposedly a “heavier” 30). I plan to try either a high mileage full synthetic or 40 weight synthetic next. I’m debating whether it’s worthwhile to just empty my oil with only 1000KMs on it and fill with one of those replacements now or wait until my next OCI.

Other than that, the engine runs perfectly. No sputtering, no rough idling, no power loss, no codes, no dash lights, nothing.

Some relevant information:

Measurement Method

When I take and record oil measurements, the car is parked the same spot and the engine is fully cooled (ie.: >= 12 hours) each time. I use a ruler to measure the millimeters between the H mark and the oil level on the dipstick. This is the officially recommended measurement procedure according to Nissan’s TSB on the later VQ35HR models to gauge oil consumption.

Driving Habits and Environment

I didn’t buy a 6-speed manual coupe to drive it like a grandma to the shops, so yes, it gets a bit of a workout. But I’m always sure to let it get up to temperature and be there for at least a few minutes before any of that, and I tend to keep it under 5,000 RPM, rarely up the redline (~7000 RPM). Otherwise, it’s light throttle and under 2500 RPM.

It does get winter driven (Canadian winters), but it has a block heater I generally keep at low RPMs in winter because of the extended warm-up time. Winter time also involves a lot more idling.

Questions:

• Obviously: what else can I try to reduce the consumption rate?
• As long as regularly ensure a correct oil level by checking and filling it when needed, how harmful is it to the engine and how does it affect longevity?