Buy a scan gauge. Easily the best "under $200" accessory you can have on a CRD Patrol.
The tell you how much fuel you used, how much you are using, fuel left etc etc
You will save $200 in fuel in 12 months easily plus never use your fuel gauge again. They also monitor boost pressure, coolant temp, engine load, Alternator etc etc etc
The only other instrument you will ever need is an EGT gauge... and maybe a tranny temp gauge if you have an auto and tow very heavy trailers.
I get 12.5 LPH averaged over 140,000 K's but my vehicle is "heavily mod'd and heavy. I clean the MAF every 20,000 K's or so but have never noticed much difference altho it probably doesn't get dirty enough to start playing up.