I'll be keeping an eye on this thread, we're planning on a Birdsville to Mt Dare crossing in June/July this year - and was wondering the same thing.
We did a week long trip to Fraser island last year, and with the mix of hard sand driving, and soft sand driving we averaged 20L/100 km, in a petrol 3.6 auto sport, fully loaded with camping gear. Bit of extra weight with winch, steel front and rear bars, 2" lift, standard 32" AT tyres.
Here is a link to the first of a 4 part You Tube set of vids put together by a guy who did the crossing from West to East in a a petrol sport in 2017. Looked to be the 3.6 pentastar auto from the interior (could have been the last of the 3.8's though). He was packed pretty light, with the exception of the roof rack full of fuel.
30L in fuel bladders, and 80L in fuel drums on the roof, 70 in the tank = 180L all up.
By the time he reached Birdsville he estimated he used around 100L.
I saw another thread on ausjeep where there was a 3.8 unlimited also carrying around 180L all up "In terms of overall fuel consumption we used 105L (from Mt Dare to Birdsville – about 530ks)" (
http://www.ausjeepoffroad.com/forum/...Simpson&page=4)
And here is another regarding a 3.8 v6:
"I used 127 litres for our crossing along the French line from Mt Dare to Birsdville, that included about an hours worth of trying every line on Big Red. 3.8 manual V6 unlimited fully loaded. "
(only provided the 3.8 v6 as an upper limit as they tend to use more than the 3.6 v6).
Cheers,
Ben.