Auto/Manual Fuel Use on sand tracks ?

Submitted: Tuesday, Mar 15, 2011 at 13:48
ThreadID: 85015 Views:4757 Replies:10 FollowUps:15
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This is our test experience and interested in yours.

The principal object of my test was to see which car is the mnost suitable for long range dessert driving (e.g. Madigan line ). With empathsis on fuel use.

I have 2 Patrols, both Petrol 4800 GU's, one auto and one manual.

We took 2 supporting cars - an 80 series manual diesel which took part in the tests and a 2005 manual Suzi Vitara and headed to Victorias Big Dessert where we have a 50km test loop which includes some impossible hills.

We went to some trouble to accurately measure the fuel usage.
The cars were levelled, their positions marked, then filled to overflowing after each test and driven back to the same places where they were filled to overflow again and fuel used weighed.

The cars were driven together over the entire test.

The sand while dry was damp underneath so tyres were deliberately set higher than normal at 24psi to increase the difficulty for the cars.

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The other aspect of the test was ability. Here the manual would win when thrashed usually getting a car length further up a hill before stopping, but several times gears were missed and if these runs were included then the auto won and was generally easier to drive until its limit was reached.


RESULTS SUMMARY
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AUTO 4800 used 8.3kg of fuel (approx 23lt/100km)
Manual 4800 used 6.8kg of fuel

I.E. Auto used 22% more in sand, so for a trip requiring 300lt of fuel load
the auto would need to carry an extra 66lt.


P.S. The diesel 80 series actually used more fuel than either petrol at 9.0kg.
I cannot comment on the state of tune of the diesel but it runs an aftermarket turbo and had larger tyres (285/75), and weighed 500kg more.

P.S. The Suzi wasn't part of the test and hence ran 12psi but it beat the other 3 cars all round - this cheezed off the big car owners but next day we were allowed to run correct pressures and the two Patrols were able to match, but not exceed it everywhere.
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Reply By: Member - Warrie (NSW) - Tuesday, Mar 15, 2011 at 14:26

Tuesday, Mar 15, 2011 at 14:26
Nothing like cheesing off the other guys!! But seriously why not run tyres at desert sand pressures of say 16-20 psi which you would be doing if you were really on the Madigan Line? And yes, autos are guzzlers, that's why my Pathfinder is on LPG.............W
Warrie

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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 15:32

Tuesday, Mar 15, 2011 at 15:32
Hi Warrie

If it was soft hot sand we would have , but keeping the pressures up made the cars work closer to the real expected load and objective here was to seperate the two cars not to try and get best consumption.
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Reply By: Member - MUZBRY(Vic) - Tuesday, Mar 15, 2011 at 14:40

Tuesday, Mar 15, 2011 at 14:40
Gday Robin
By weight the diesel use and the auto use are almost the same as the SG of both fuels are different by a few %?
Muzbry
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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 15:38

Tuesday, Mar 15, 2011 at 15:38
Hi Muz
Yep there can be a diffwerence in fuel weight , our system measured them at 0.74 g per litre , but it wasn't meant to be a diesel / Petrol test. The 80 series was along for the ride and so I was happy that the combined errors were within the target range.

It was a fascinating result though and I suspect that the 80 series was over tyred for its low power level and in combination with its extra weight was just to much.
The Patrol and Suzi had the power to accelerate and wheelspin until they just lost traction whereas the diesel just died thru lack of go.
Mirrors other tests I have done with Patrol diesels.
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Reply By: Shaker - Tuesday, Mar 15, 2011 at 16:33

Tuesday, Mar 15, 2011 at 16:33
The result surprises me, I would have thought the auto would have fared better, after seeing a bog standard Hyundai Terracan petrol auto go up & over Big Red like it wasn't there!

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Follow Up By: Member - Stephen L (Clare SA) - Tuesday, Mar 15, 2011 at 19:09

Tuesday, Mar 15, 2011 at 19:09
Hi Shaker

None of the standard Simpson Tracks, including Big Red compare to the real terrain of the northern Simpson, where you do not have the luxury of any type of run up.

Also the weight that your vehicle carries for a northern Simpson is far greater than a normal Simpson trip, which again will have a very big impact to fuel economy.



Cheers


Stephen
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Follow Up By: Shaker - Tuesday, Mar 15, 2011 at 21:16

Tuesday, Mar 15, 2011 at 21:16
Hi Stephen, I understand what you are saying, but Robin was in Northern Victoria for his comparison test.
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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 21:37

Tuesday, Mar 15, 2011 at 21:37
Hi Shaker

I think you may be reffering to the manuals better hill climbing in this particular case, and it interesting to examine it more closely.

I have no doubt from my other drives that the auto can be better in most soft sand situations , but Stephens point about no run up is what allowed the manual to get further.
It was a momentum thing I believe , and the manual does not have the autos transmission loss - basically giving it more power to play with.

In many cases as soon as gear change is required then the manual suffers , but here the manual needed no gear changes , just high 1st point and shoot.
I guess in really soft sand the manual would dig in first , but here the sand was not seriously soft and power though the clutch required no special effort and wheelspin on take-off did not occur - hence the senario did not play to the auto's strengths.
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Reply By: gbc - Tuesday, Mar 15, 2011 at 17:32

Tuesday, Mar 15, 2011 at 17:32
Sounds about right. We have manual and auto diesel 4wd colorados in our fleet. By the fuel card bills, the manuals average about 9l per 100. The autos are 12l per 100. That's an average over 70 000 kms.
The surprise package is the petrol colorado (commodore v6) auto which is matching the diesels and I know it gets a belting.
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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 19:25

Tuesday, Mar 15, 2011 at 19:25
I hear that engine is bit of a winner gbc
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Reply By: Axle - Tuesday, Mar 15, 2011 at 19:58

Tuesday, Mar 15, 2011 at 19:58
G/Day Robin, ...What about gear selection, between the two?, eg, was auto locked in a gear or just drive, Low or high range?, I know with the toyo V8 5speed, the throttle sensor position can make a huge difference, in hard going, its better to be on the high side of revs than letting it work to hard ,otherwise you can/t keep the fuel guage off empty,, lol,


Cheers Axle.
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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 21:01

Tuesday, Mar 15, 2011 at 21:01
Hello Axle

We actually did a number of tests over 3 days , but for the fuel test the auto was in drive high range, to basically give the lowest number of revs over time.

This is because max fuel efficentcy occurs loaded at below 2000 rpm - mind you there is little choice as even though this auto has a tiptronic mode it frequently decides to do its own thing and change gears up as it experiences load.

For the most difficult power runs we would use low range , although you had to be careful as it would spin all 4 wheels without hesitation and indeed I remember one hill very well were you would back off get traction back off etc.

The results we got fitted well with our normal high country type driving patterns and this test simply allowed us to confirm and put figures to the common knowledge that autos use more when worked.
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Reply By: Member - Phil G (SA) - Tuesday, Mar 15, 2011 at 20:07

Tuesday, Mar 15, 2011 at 20:07
Gday Robin,
I'm guessing you're planning on doing the Madigan Line in the future.
If you want something similar to the Madigan line, you need to find some spinifex hummocks rather than sand! For a lot of the Madigan Line you will be crawling at about 10kph and lurching from side to side over spinifex. An automatic is naturally easier to drive, but with a manual I found most of the time I settled on 3rd gear low range and sat between 800 and 1200 rpm as the Toyota diesel chugged along. I expect your petrol motors will want to run higher revs.

As a guideline, David and Joan Owen used to run Madigan Line trips. From Alice Springs to Birdsville, their recommendations back in 2004 were 240 litres for 4 cyl diesel; 300 litres for 6 cyl diesel, and 400 litres for a 6 cyl petrol. They didn't distinguish between autos and manuals - I guess autos were less common back then. On our 2004 trip my TD man Prado used 170 litres, and the 6 cyl diesels were between 210 and 240 litres - the 210 was a N/A 1Hz and 240 was 1Hz with aftermarket turbo.

We had a FZJ105 (6 cyl petrol) auto Landcruiser with us on our 2006 trip and I can't recall for sure but I think it used a bit over 300 litres between Mt Dare and Birdsville, which was about 50% more than the diesels. A lot depends on the conditions at the time and route taken. Based on the desert trips I've done, I'd be guessing an auto uses 10-15% more fuel.

Cheers
phil
AnswerID: 448364

Follow Up By: Ozhumvee - Tuesday, Mar 15, 2011 at 20:37

Tuesday, Mar 15, 2011 at 20:37
I was going to mention what Phil has said, both the different terrain and the ease with which the auto's work in really slow going.
We had three auto's and one manual when we did the Madigan, TD6 79 series, 3 litre TD Patrol auto, 2.8lTD Jeep and my Humvee. As you would expect the Humvee used the most but it was also the easiest and most comfortable to ride and drive, it absolutely revelled in the terrain and on the worst bits (2days of sub 10kph ) it used 24l/100k. The next highest consumption was the 3L GU at about 21 l/100, then the 79 series at just under the 20 mark and the Jeep which doubled its consumption to 14l/100!
The 79 series passenger was wishing they were somewhere else at the end of the day after being thrown around all day. We found that around an hour and half to 2 hrs was as long as you could travel without a break on the worst bits.
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Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 21:21

Tuesday, Mar 15, 2011 at 21:21
Hi Phil , Peter

Thanks for taking the time , yes I have experienced some of that tusscock driving and found it quite debilitating.
I hope the weather allows our trip.

Good to see your results were generally in the direction of mine.

I like to confine my comments to just these two patrols because I believe the results would not be the same with the two versions of the 3lt Nissan.

The main difference being that the manual 4800 has a large flat torque curve and just lopes all - mine has been down to 300 rpm on a dyno without stalling and this keeps speed steady.

By comarison the auto's can sense load change when they encounter a Tussock
and react by changing a gear or invoking the torque converter.

The general reaction is resistance (tussock) power injection - go over obstackle (to fast) - engine load drops and the auto backs off - overall effect is uneven.

In the manual, locked in gear this can't happen , but only provided the engine has the stored energy to overcome the obstackle - and this is the key , I believe to the lower fuel use.

In a 3lt manual (patrol) the amount of torque off turbo is to low and an injection of fuel is needed creating a jerky bumpy ride making the auto version feel better.






















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Reply By: Pete Mac - Tuesday, Mar 15, 2011 at 20:56

Tuesday, Mar 15, 2011 at 20:56
Little surprised that the difference is that much...We know Auto's are thirstier, but I would have thought the Auto should just lope along...I know that it's only in really soft sand that I have to give my 4.8 Auto a kick in the guts - apart from that 1/4 throttle as best I can...Maybe with lower tyre pressures?

This is pretty subjective commentary though...you have done the testing :)

Certainly I'd think there is no question that the Auto would be an easier/superior drive in sandy country...but if the fuel consumption is that much more?

Just my thoughts,

Cheers,

Pete
AnswerID: 448368

Follow Up By: Robin Miller - Tuesday, Mar 15, 2011 at 21:28

Tuesday, Mar 15, 2011 at 21:28
Hi Pete

It is tricky , and there are several senario's which give different results.

When I first got this auto 4800 I took it straight to stockton beach and she was lovely , much smoother and easier to drive. If however you are driving along a dirt track with a 200mm tree across it the manual is a lot more consistent and smooth as it retains the same gear - the auto can only sense load - apply power to correct , overspeed , then reduce load as it comes off the tree - this costs fuel.

As Phil is saying above - its lumpy Tussock type driving and this is like the tree senario.
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Follow Up By: Off-track - Tuesday, Mar 15, 2011 at 23:43

Tuesday, Mar 15, 2011 at 23:43
Pete, the main reason why auto's use more fuel is by design they utilise a fluid coupling whereas manuals are mechanically coupled. Unless in locked mode the auto, or more specifically the torque converter is the source of some power loss through the drivetrain which keeps the engine working faster/harder than if it had a manual box.

Mind you poor gear selection in a manual will close the gap.

Apologies if instructing how to suck eggs.
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Reply By: Crackles - Tuesday, Mar 15, 2011 at 22:26

Tuesday, Mar 15, 2011 at 22:26
"...headed to Victoria's Big Desert where we have a 50km test loop which includes some impossible hills."
Ok, you have me interested Robin. Where are these impossible sand hills in the Big Desert??? :-)
Cheers Craig.............
AnswerID: 448376

Follow Up By: Robin Miller - Wednesday, Mar 16, 2011 at 07:48

Wednesday, Mar 16, 2011 at 07:48
Hi Craig

I think you know my brother from Benalla - he was driving the 80 series diesel with big tyres that was the worst performing of our 4 cars.
He can tell you more.

The photo though was taken on the second day on the middle run up to Thompsons peak (in places) . That hill wasn't impossible on this day as sand was part damp, but still only my auto 4800 made it up on first run.
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Reply By: get outmore - Wednesday, Mar 16, 2011 at 03:21

Wednesday, Mar 16, 2011 at 03:21
mmmm talking of missed gearchanges in the manual demonstrates to me the inexperience of the drivers

I dont change gears

right tyre pressure and 2nd low

nothing else will get you further

run ups are totally over rated I genarlly have a 10-15m runup - just enought to get 2nd low reveing - thats all thats needed

I did a run from the baxter cliffs to esperance folowing the beach as much as possible using just the factory diesal 80 series tanks 17l per hundred

one of the mags while testing the 4.8 in sand had no worries seeing 100l per 100ks of fuel usage with photogrphic evidence of the trip computer

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Follow Up By: Robin Miller - Wednesday, Mar 16, 2011 at 07:36

Wednesday, Mar 16, 2011 at 07:36
Hi Get out more

Come along on our next trip - nothing but power and momentum will get you up some places we go - and then not even that works.
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Reply By: Ray - Wednesday, Mar 16, 2011 at 08:39

Wednesday, Mar 16, 2011 at 08:39
I had a Daihatsu L10 years ago and that would go where others feared to tread
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Follow Up By: Robin Miller - Wednesday, Mar 16, 2011 at 09:13

Wednesday, Mar 16, 2011 at 09:13
Hi Ray

I can well understand that

I love direct drive off comparisons - it tends to put the talk into the background

After our controlled tests a 4.2 diesel worked over patrol joined us, it also had bigger 285/75 tyres like the 80 series , we now had the 3 petrol cars with high power to weight ratios all with smaller tyres powering around and both the two 4.2 diesels , 1 nissan 1 toyo, were clearly underpowered (over tyred?) for this type of terrain.

We eventually got'em up this hill but note the black smoke from the effort this one needed.

**** Had good photo here but I think the server still can't locate photos - but will try to load another time.

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Follow Up By: Robin Miller - Thursday, Mar 17, 2011 at 07:50

Thursday, Mar 17, 2011 at 07:50
Looks like images are now loading ok - this car made this peak but sure had to work hard !




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