warthog posted:

I have a 4.2td and am using about 17-18/100 when towing our big red kanga camper at 100-110. My belief is that the 3.0 is definitely the more fuel efficient engine. The td42's strengths are low down torque and reliability. I don't consider mine at least, as particularly fuel efficient.

desert posted:

Warthog, your figure of 18lts/100 is around what I once got when first running-in my Patrol and I was pretty disappointed in that after crossing over from a cruiser returning 12/100. There are several, inexpensive modifications you can under-take to make the 4.2 more fuel efficient. Firstly, junk the entire exhaust system and custom fit a 2.5 inch, mandrel bent complete system utilising a straight-through or "turbo" muffler. Cost around $400. Secondly, the "dump" pipe from the turbo outlet can be changed for a less restrictive version. Cost around $150 plus fitting. These two mods will pull back your consumption to around the 15lts/100. To squeeze another saving of around 1 lt/100 is going to be expensive, about $2000 for a top mount intercooler which can allow a slight increase in fuel delivery. Sounds wrong, but with cooler air you can add slightly more fuel for more power which will equate to some savings in some conditions as the engine finds it less of a labour to do things due to more horsepower. From here, the mods start getting more technical for less of an obvious gain and unless you have a specific need for increased horsepower, you will not gain much more in economy. Yes, you are correct in generalising that the 3 litre is more fuel efficient. Up to a point, however when the little motor has to work hard, it's high-tech fuel metering cannot compensate for the need for cubic capacity and here it's rate of fuel usage actually surpasses that of the 4.2, given the same load.