G'day John, the coolant reservoirs are for the radiator HEADER tank, that's the one on top, the one on the bottom is the OVERFLOW tank, and should never be higher then the mark thats marked on the tank. Be careful you don't damage these tanks when you lean over the engine to check out the engine bay for anything, with age they become brittle and easily damaged during servicing if abused or leaned on for any reason.
The coolant goes into the overflow when things get HOT, then returns to the header tank when things cool down.
IF the OVERFLOW is ever full ABOVE the mark, you'd better keep serious tabs on what's going on under the bonnet.
Enusre that your coolant is of the ORGANIC type, (Genuine Nissan, or Red stuff from auto suppliers marked ORGANIC) this is very important with the 2.8 as the alloy used in the head corrodes very easily as does the head gasket causing problems you don't want to hear about, suffice to say, a head replacement will set you back in the vicinity of $4,000.
So to avoid such, flush out your system thoroughly, the ORGANIC stuff, DOES NOT MIX with the Non organic, which will turn solid if mixed and block passages that you don't want blocked.
Make sure your radiator is NOT blocked, especially behind the A/C condensor, where crap gets trapped easily, thus reducing the capacity of your radiator, make sure the fins are not broken off externaly and not blocked, sometimes it's neccessary to remove the radiator and have it *RODDED* (meaning rods are forced thru the tubes to clear blockages) the radiator cap is working as it should, if questionable, replace with genuine.
Sub tank operation, Nissan state the subtank transfers fuel on start up for a short time then stops.
How I use mine, I wait until the main tank is 3/4's full, then hit the subtank button allowing transfer, when the main is full, transfer stops, that way I use both tanks preventing build up of algae in either.
I get just under a 1,000 K's from both tanks. I've also found the 2.8 runs smoother, quieter and happier on Gull Bio diesel.
I have a KLEENOIL bypass filter fitted to my Patrol that filters out the minute particles produced by un burnt diesel produced in all diesel engines in an attempt to gain maximum longlevity from the engine and my oil. So far, it seems to be working exceptionly well.
Regards the manual, I purchased the Nissan Workshop Manual shortly after I bought the car, the manual I bought from a book store in town costing $500. There are no less then FIVE seperate books involved, but they certainly cover anything you'd ever come across.
Recently I gave away a CD manual, that I bought off the internet, from a source pointed out to me by a guy on patrol4X4 for $10, I'm sure they are still available .