Thanks for the response Whitie.G'day Tuco, IMHO I would not be putting in a 5W30 into an engine being operated under Cairn's climate.
If you are comfortable with the Mobil 1 (5W50), then stick to that. It has a B3 rating so will be ok under the Nissan warantee however the oil is not specifically made to cope with EGR deposits. Having said that, I would give it a try and get the oil analysed at 5k to see how it is coping with the EGR, they may say that it is still ok to keep until the scheduled 10k service interval.
Worst case, you would need to change it at 5k intervals.
I'm still a bit confused at your not puting 5W30 into the vehicle in "Cairns' climate". Cairns has a tropical, coastal, climate with periods of high rainfall and high humidity. I'm not sure how the rainfall and humidity would affect any engine lubrication at all.
Mean average temperatures in Cairns are significantly lower than many southern capitals.
From the BOM site -
Brisbane - mean average monthly maximum. 29.4°C
Absolute maximum recorded temperature 43.2°C (over 99 years 1887-1986)
Sydney - mean average monthly maximum. 25.9°C
Absolute maximum recorded temperature 45.3°C (over 153 years 1859-2012)
Melbourne - mean average monthly maximum. 25.9°C
Absolute maximum recorded temperature 45.6°C (over 157 years 1855-2012)
Hobart - mean average monthly maximum. 22.5°C
Absolute maximum recorded temperature 40.1°C (over 54 years 1958-2012)
.. by comparison..
Cairns - mean average monthly maximum. 31.4°C
Absolute maximum recorded temperature 40.5°C (over 69 years 1942-2012)
The figures indicate that Cairns absolute maximum is only 0.4°C higher than Hobart while some 5°C lower than Sydney or Melbourne.
Hardly any reason to put a thicker oil in I would have thought.
I agree with regard to the oil analysis - having done the exercise with Mobil tech services after we swung the Toyota Hilux Surf (1KZTE turbo diesel) onto Mobil 1 5W-50. This was done to ascertain a safe oil/filter service interval on the synthetic. The Toyota spec is for 5000K oil and filter change using mineral oil. We did sampling at 3 intervals - 10K, 15K and 20K. At 20K the ash level was too high - probably due to clogged 2 stage oil filter.
Interesting was the fact that with a 15K oil and filter service interval the Viscosity Index of the Mobil 1 sample was still better than new mineral oil! Amazing!
Spoke with my local Nissan dealer today - and they recommend 5W-30 - as per the owners manual.
With that in mind I will most likely use the Castrol Edge Sport 5W-30 and do an oil analysis on the next 10K change.
Thanks again for your input.