2nd Fuel Filter - before or after factory filter

http://www.dieselcare.com.au/which-filtration-kit-primary-or-secondary

If you have a water sensor light on the original fuel filter, its a good Idea to put one in after that. Reason being, when the light comes on it's not too late (as is sometimes the case). A filter with a visible bowl is a great idea. Too!

Josh

Before (upstream) from the OE filter.
That way when you change, there are not contaminates going downstream without a filter to catch
Better to install for the same reason
And, for one reason or another my dealer will honour the warranty if upstream but not if downstream.
All filters are really better as pre-filters IMO
CJ

Another vote for primary rather than secondary.

It all depends on the micron size you are going to use.
If fitted between the OE filter and the engine you have to be very "clean" with the installation. "Meticulously Clean" otherwise you will introduce "thing's" into the direct line to the High Pressure pump. Most people do not know the meaning of clean.

A filter fitted there will render the OE restriction sensor inoperative if the new one restricts.
So, unless it too has a wired in alarm for restriction, then the OE will not detect the new filter has blocked. It shouldn't of course.

They can work well there but if restriction occurs you will only know by performance loss.

Filters fitted before the OE filter retain the operational/sensing of restriction if either/both filters restrict. Many are fitted with a larger micron than OE so there is a gradual removal of contaminants. The New filter should have/be a dewatering filter which has a really good go at eliminating emulsified water held within the fuel molecules.

Just a bowl or a Water Watch filter can catch and/or alert the water is there, but the emulsified water can go through and usually has unless there is a filter which is designed/featured to catch it.

Nothing is perfect, but a suitably selected filter which dewaters, finely filters, has a visible bowl and perhaps water detection wired also to the vehicle is a good start.
A suitable flow rate is essential to have proper performance without premature restriction occurring. Most 3 litre engines require 120L/H flow rate or more, so some contaminant catch can happen without having to change the filter every short drive. Some are too small in flow rate.
A 2011 Dmax flows about 35L/H and so a x 3 factor seems suitable for the filter size.

I installed mine before the manufacturers, reason being, last time I picked up a tank of bad fuel was during floods.
So removing/draining etc is carried out before the main filter during bad weather.
My pre filter has a clear water trap/ water alarm and an aquabloc filter of 30microns.

Top End, we have an additional filter fitted to our 2013 D-Max.Click here there are some helpful comments at the bottom which cover some specific details. Cheers, Kanga.