GU 4.2 td Oil

The main thing to do is check the oil grade required. This is different to the oil viscosity (ie 10W40). You can vary the oil viscosity based on where you drive (say 20W50 for desert or 5W/30 for Snowy mountains) but you should NOT vary the oil grade.

The Nissan manual has a chart for recommended oil viscosity for different ambient temperatures, but always specifies the same oil grade. Many people inadvertenly buy an oil based solely on the oil viscosity yet neglect to read what grade it is.

My Patrol manual specifies CF(4) grade for the 3.0TD and specifically states NOT to use CG(4). I am pretty sure from memory its the same for the 4.2TD, but check your manual to confirm.

Also, I would not use a lower grade oil, eg CD, if you intend to keep the vehicle, even though the manual says its acceptable. I would always use the highest allowable grade. (note; The SG, SH, SJ etc. grades are for petrols while CF, CG etc. are for diesels)

There are many factors to what makes up the different grades but, simplistically, a higher grade oil provides better protection, typically at higher temps. However, the additives required to achieve this can affect other properties.

Its my understanding that, amongst other things, the CG(4) diesel oil has less detergents than the CF grade to improve other properties. But this now reduces the "cleaning" ability of the oil and can lead to blocked oil galleries in extreme cases. Its also this reason why its good practise to change diesel oil every 5,000kms even though many manufacturers recommend 10,000 or longer service intervals. Its not that the oil no longer lubricates, its because the detergents in the oil are used up and can no longer keep contaminants in suspension (ever washed greasy dishes and halfway through you had to add more detergent?)

Cheers

Mark
(Chemical Engineer)

Yeh Mark and Rowler- basically agree with your info so far.
The problem with saying only use as specified in your manual is that oil is continually improved and specs change.
Thus if you have a 10yr old Patrol the oils available then are very different to those available today.
As an example my sons friend bought a pristine HK Holden (1968) which listed "MS" oil as the requirement, both on the the rocker cover and in the manual. He asked me "what is an MS Oil?" MS Grade oil was last manufactured aproximately 30 years ago if my memory serves me correctly.
In most cases newer oils are better in every respect- there may be rare exceptions, and there is some debate about the later spec Diesel Oils on earlier motors- but personally I believe as long as your service intervals are OK then you can't go far wrong by going for the latest spec oil. Incorrect Oil viscosity is potentially a far greater problem.
Bypass filtering is another thing to consider- It will extend the life of your oil AND motor as it will filter out much finer contamination than the full flow filter.
Cheers

Dave
Suggest you look at Filter Technology
And Frantz Filters

Yes, you do keep your old full flow filters- but you can change them much less often.
Bypass filtering uses a small volume of oil bled off from a convenient point (often the oil pressure sender via a Tee Piece) which then is filtered through a deep filtration media - literally toilet paper for the Frantz filters!
Thus you get filtration of particles down to a fraction of the size caught by normal "Full Flow filters.
The benefits include longer oil life, longer engine life, and long term cost savings as you keep the filters forever and transfer them from car to car.(Saving money as you use less oil.)
I have been using them for many years (since about 1970 in fact!) on a number of vehicles with exceptional results. One of my filters has been on five different cars! They can also be used on DIESEL FUEL to great effect (when you consider the fine tolerances in your injection pump and injectors this is not surprising!)

Finally also if you do a search you'll find heaps more info.
Cheers