Well, we made it ! Quick summary of the trip and some observations for those interested.
The Trip: Brisbane-Roma-Longreach-Boulia-Tobermorey Station-Gemtree (Donahue and Plenty Highways); Alice Springs - Yulara-Alice-Tennant Creek-Barclay Homestead-Mt Isa-Winton-Blackall-Roma-Brisbane.
We were limited to 3 weeks given school holidays and little flexibility given by the kids schools plus ours on is a gymnast and trains at the Brisbane High performance Centre and they would only give 3 weeks off training.
Sarah and I both noted many, many places we want to come back to one day and spend much more time. Both of us had done most of "the Red Centre" before (Sarah having spent time in Alice as a youngster and me having done the Adelaide-Oodndatta -Finke Track trip twice in last 6 years). Our kids hadn't done any of this area though so they were very excited. We didnt mind missing what we had been two a few times before (eg Kings Canyon, Boggy Hole etc). We did do day trips to both East and West McDonnell Ranges while we were based in Alice Springs (6 nights there). Big highlight for me this time was climbing Uluru (on my third trip there in the last 6 years).
Total Distance: 7235km's. Vogue Trip computer "B" said 18.8l/100km.s My beancounter calcs said 20.1l/100km via receipts. I'll have to work out how to use my GAP IID tool to correct the trip computer!
The Car: MY12 SDV8, 50K on clock; Has a few basic mods (bash plates, 285/50 Coopers and UHF, DBS and fridge etc). We had two spares on the roof (wheel well empty) and the Van has two spares on the front. the car Performed flawlessly. We had one brief moment of "pause" as we approached the last 50km's of the Plenty which was horrendously corrugated and had us at 25-45km/hr for ages. Suddenly we had a few faults (park brake, no air cond then "charge fault"). We stopped at Gemtree and as I suspected discovered one lead to the battery too loose. Tightended and all faults disappeared. That was the extent of any issues on the trip.
Gearbox: We ended up doing a lot of the return trip cruising at 95-100 in 6th as the car seemed most happy at that speed and gear. I was also tired of every 200 series LC owner telling me to tow in 6th (4th in a LC). I don't know what our gearbox temps were - would have been interested to know. We experimented with 6th, 7th and 8th at various times. Used 7th a lot on the way there and we had one long period with a tail wind to Yulara from Alice where we sat on 1250rpm in 8th effortlessly (17l/100). But most of the time it was labouring in 8th at 100 and we stuck with 7th and then later 6th (Winton-home).
Fuel Economy - as above - 20.1/100 for 7000km. I am guessing van at 3300-3500 depending on water tanks (2650kg Tare). An extra 40lites of fuel tank capacity would have been nice - but we coped fine without. Needed to stop regularly anyway with kids so just filled up at 1/4 left - no shortage of towns - easy.
Suspension: No issues. CVD's fine - no sign of leaks. Checked them regularly on the Plenty which was really bad at times.
Very comfortable, towed perfectly, no steering lightness, perfectly level. Around 250-280kg on the ball per scales I used when we left and mid trip (emptied front water tank to reduce it).
Bit of dust ingress around rear tailgate, which started to stick shut by end of trip. All good now after some liberal use of WD40.
Tyres: - brand new Coopers 285/50/20 on rear; Near new on front; two spares. Pressures: 38 front 44 rear at full weight; Off road: experimented a bit: 30-34 front and 35-38 rear at various times. Used a 8 tyres TPMS (Tyre Dog) and found pressure and temp monitoring very useful. No punctures. Definite wear on rears in particular but not much chipping.
The Van: As I'd hoped from a Bushtracker - faultless too. It really feels like 2 things: 1. it will outlast the car and most vans by about 20 years. 2. Its really, really heavy. No wonder you see F250's and Chevies towing them in the outback. But I cant fault it. It did everything we asked of it and was super comfortable and easy to tow. I'd like a bit more solar power so will add a couple more panels in due course and its simply too heavy to use all 6 (yes, six) water tanks given they are 90litres each. I have no doubt we were at GVM and gross train weight at times early on until we got across the Plenty and relied on caravan park water and kept tanks very low.
We bought it 2nd hand and spent a bit on it at the factory to bring it from 2004 to 2015 spec, at half new van cost. So, many more happy trips to come I hope.
In conclusion, a long planned trip was a tremendous success with no breakdowns, punctures or any accidents, health issues etc. We were lucky no doubt - esp re tyres- but we were very sensible and careful and drove to the conditions. Very happy family who all loved the trip - and Mrs M did note that "her" car was perfectly behaved.
Highlights: Too many to list - Uluru (again), Tobermorey Station (for its remoteness and a magic evenings); ditto Middleton Hotel and Boulia; and I always love Alice and the Ranges!
Overtaking a triple road train with (relative ) ease.
Lowlights: seeing a D3 and camper on back of truck coming back to BNE from Mt Isa; Lack of L322's in the Outback. We saw two.
Hope the above is of some interest! feel free to ask questions!
Cheers

