Fuel consumption...yikes!!

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sundowner2
Posts: 3
Joined: Sat Oct 17, 2020 6:56 am

Fuel consumption...yikes!!

Post by sundowner2 »

Hi all, considering the purchase of a new MUX-LS-U, they have some pretty good deals going at the moment (Tow pack included in the price). But I have a question; for the past eight years we have towed our Jayco 2 tonne caravan behind our Nissan Navara, fuel consumption when towing averaged around 15 - 18 L/100km which I considered to be acceptable.
In my research on the MUX I was shocked to read a road test for a MUX towing a 3 tonne caravan at 25L/100km!!....what??. That's the sort of stuff I'd expect from a petrol V8, not a 3 litre diesel.
Does anyone out there actually tow a 2 - 3 tonne van and has recorded consumption figures?....much appreciated.
Paul
mydmax
Posts: 1704
Joined: Sat Oct 12, 2013 8:36 pm

Re: Fuel consumption...yikes!!

Post by mydmax »

Sundowner2
I do not have an Mux but tow with a early Dmax. towing nearly 2 ton the fuel consumption is around 12 to 14 depending on what the conditions are. Mine has some economy loss with injectors which will require replacing sometime soon. The Mux are almost universally reported as being the most fuel efficient while towing especially 2wd models. Therefore, the report which has alarmed you may have been crossing the Nulla with a really strong headwind heading to WA, or the person driving is not doing it well. If the van has huge frontal area and there is no wind diverters to run the air up and over the van I suppose the fuel figure will be higher. Generally not anywhere near what you report. Your Navara figures are quite high in relation to most with 3 litre diesels.
Bob
Posts: 721
Joined: Sat Oct 12, 2013 10:25 pm
Location: Baldivis WA

Re: Fuel consumption...yikes!!

Post by Bob »

Firstly to tow 3,000kg with the MUX is pushing the envelope and I would not be surprised if you are not exceeding some of the weights be it GCM, GVM or whatever.

I tow 2,500kg with my D-Max and would not like to take that to 3,500kg never lone 3,000kg. At 2,500kg it sometimes feels like you are towing a house behind you.

As for fuel consumptions I have recoded between 12 to 22L/100 depending on head winds, speed, terrain etc. I had a long range tank fitted by the dealer and I work on a range of 550km between refills.

My previous car was a Challenger with much the same size tank as the MUX an virtually had to fill up every 200km my wife told me I could buy the car as long as I fitted a bigger tank. Around town I get 1,000km per tank.
2014 LST Ash Beige. SMM Steel canopy, Outback Drawers, dual battery with 2 x 160W solar panels (keeps the beers nice and cold), 135L tank, TJM T15 alloy bar with Xray-vision LED lights, Dumbo Clearview Mirrors. The ultimate tow truck.
sundowner2
Posts: 3
Joined: Sat Oct 17, 2020 6:56 am

Re: Fuel consumption...yikes!!

Post by sundowner2 »

Thanks for the responses people....I very nearly made a big mistake...almost signed on the dotted line for a new Pajero but just in time I checked the towing specs....max tow ball weight; 180kg!!...what??....what sort of fricking caravan can you tow with that??...my 17' Jayco Outback puts 173kg on the ball, unladen!!....so I'd be able to carry just 7kg!!

The MUX certainly seems to get great towing reports....some good deals around right now too.

Thanks again
Paul
Lockyer Valley, Queensland.
mydmax
Posts: 1704
Joined: Sat Oct 12, 2013 8:36 pm

Re: Fuel consumption...yikes!!

Post by mydmax »

Sundowner 2
Yes the Pajero, while a nice comfortable vehicle can't tow much legally. I wonder if that is because it has no chassis and no basic inherent strength. The independent rear is also a concern as it splays when loaded and unless correction of some nature is applied then it bums down. The MUX will sink too but can be corrected. Although a Pajero may be rated to tow 3 ton it certainly is at the max, ie,flat level road, no wind, no hills. just a max capability in ideal conditions. My Isuzu is rated at 3 ton but going much past 2/3 of any vehicles claimed ability is surely pushing it. WE do have wind and hills in Oz don't we?
If the ride height is near original or higher when towing, it means the suspension still has the ability to "absorb" road shocks and undulations and so be able to keep stability under control with good shocks. The OE shocks may not be able to control high load and towball mass under adverse conditions. It is supplied with shocks to suit the basic vehicle, alter the dynamics and the ability is lost somewhat.

I can move my 2 ton Dmax out of the carport by pushing or dragging it, That must mean "I" am rated to tow 2 tonne, yeah sure!
Danno
Posts: 3256
Joined: Sun Oct 20, 2013 1:23 am
Location: Darwin... sort of.

Re: Fuel consumption...yikes!!

Post by Danno »

The Pajero's towball weights are not straight forward, i'ts actually 250kg towing up to 2.5 ton and 180 from 2.5 to 3t. As for it's "lowly" 3T rating everyone knows the 3.5T rating on the new utes is BS, it turned into a marketing exercise a long time ago and is just a bs figure they quote. Most if not all of the utes can only legally tow 3.5T if there is no gear, no fuel, no mods and no-one in the vehicle which is good because anyone that tried it would be a nutbag or probably dead.
Cheers
Dan
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sundowner2
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Re: Fuel consumption...yikes!!

Post by sundowner2 »

I agree, towing limitations is a very misunderstood subject, an ongoing legal case here in Queensland concerns a gentleman who brought a caravan from a dealer and was told it was suitable for towing behind his Prado, the Prado has a 3000kg limit, the van has a tare of 2870kg. Of course as soon as the fridge was loaded with XXXX and the plates and cutlery stuck in the drawers the van was overweight....he complained and was simply told that the dealer had done nothing wrong...the Consumer people are involved now but they also think there is little the bloke can do.

One really important weight factor that few consider is the tow vehicles stated GCM or Gross Combined Mass, this figure (5750kg for an MX-U) is the absolute allowed weight of the vehicle and anything hanging off it, this weight can never be exceeded.

And I do know this, with my involvement in the insurance industry, in an accident involving a caravan all weights will come under scrutiny, go a kilo over and kiss a claim goodbye.
Paul
garrytre
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Joined: Wed Feb 05, 2014 4:22 am
Location: adelaide hills

Re: Fuel consumption...yikes!!

Post by garrytre »

sundowner2 wrote: Sat Oct 17, 2020 11:45 am... just in time I checked the towing specs....max tow ball weight; 180kg!!...what??....what sort of fricking caravan can you tow with that??...my 17' Jayco Outback puts 173kg on the ball, unladen!!....so I'd be able to carry just 7kg!!
Not sure I understand this. I would have thought that if you start with your 180kg tow ball weight, then put plates,cups, a fridge, half a cow, and a pile of tools behind the caravan's axle, then you'd have less tow ball weight. All that stuff weighs way more than 7kg. Like, the tow ball weight isn't the same as the caravan + load weight, most of which is on the axle.
If it ain't broke, fix it til it is.
garrytre
Posts: 648
Joined: Wed Feb 05, 2014 4:22 am
Location: adelaide hills

Re: Fuel consumption...yikes!!

Post by garrytre »

sundowner2 wrote: Sat Oct 17, 2020 7:11 am ... Jayco 2 tonne caravan ... 3 tonne caravan ... 2 - 3 tonne van
The weight of your van is probably the least relevant thing to fuel consumption. Consider the air resistance of a flat tray with 3 tons of steel, vs 1 ton of empty wooden boxes.

At normal highway conditions, the amount of fuel you use is affected by

Your weight
- going up huge hills -but really, how many of those do you go up?
- accelerating -how often do you do that?

Tyres changing shape and producing heat.

Air resistance is the big one. Again all sorts of things affect that.
- the frontal area of the thing moving through the air, so eg a caravan vs a pop-top campervan.
- roughness - your bull bar, driving lights, roof rack, ute tray, mirrors, square edges all convert laminar flow to turbulence.
But they're pretty much fixed, ie you can't really change them in the middle of a trip.


The air-speed you're doing is really the biggest air resistance thing that you can control at highway speeds.
So not road speed, 100km/hr, but air speed, that is affected by how fast, which direction the wind is blowing.
If you're doing 100km/hr into a headwind of 20km/hr, your airspeed is 120km/hr.
If you're doing 100km/hr with a tail wind of 20km/hr, your airspeed is 80km/hr.

Here the actual physics gets pretty messy, (Reynolds numbers, Stokes equations, laminar vs turbulent, blah blah, plus the fact that we have engines with torque curves and gearboxes, not electric motors) but it's fair to say the power you need (think fuel) goes up with airspeed squared.
8**2 = 64
12**2 = 144
so with the 20km/hr headwind you're using twice as much power (think fuel) as with a tailwind.

Or
with your 20km/hr headwind, if you slow down to 80km/hr, your airspeed is 100km/hr.
10**2 = 100
- about 2/3 of if you were doing 100km/hr.

In practical terms
- slower into a headwind saves more fuel than you thought.
- choose the right weather, right day, right destination to suit the wind.
- a pop-top is better than a full height caravan.
If it ain't broke, fix it til it is.
mydmax
Posts: 1704
Joined: Sat Oct 12, 2013 8:36 pm

Re: Fuel consumption...yikes!!

Post by mydmax »

With an MUX you are better off than with a Dmax as the axle to ball measurement is less, Inherent stability increase I think. Having a Jayco with 170+ kg on the ball seems far too much. Just how much downward increase on the rear tyres do you have to have to optimize the grip?( Many caravans are stupidly heavy.) If not for that, what else is it the downward force is for. Most lift the front which makes it unstable too. The front and rear tyres and the pressures would have far more effect on that, along with good controlling shocks able to cater for the additional mass transfers when cornering and braking and undulating travel. Insurance companies would only have the ability to calculate total mass for denial of insurance as with many accidents, who knows where the stuff was positioned in relation to the ball and the axle/s after it is dozed up off the road. I agree with Garry, most seems to have the foot down to keep the timetable happy rather than save fuel. X number of tons takes X number of $ or Litres to move the same distance. It is called work. Increase the work rate or stress and more fuel used. The fuel efficiency of the engine has a small positive effect. Isuzu seem to do fairly well there.
PS, A mate of mine has a 105 series LC and tows a 3 ton van. His original rear shocks are stuffed, not leaking but stuffed. The mechanics don't check because of no van on back. I have travelled in the vehicle empty and immediately mentioned the shocks not doing CONTROL. He refuses to see there is a problem. However, follow him down the road with the van on and he could weave a nice basket for you. Accident going somewhere to happen?
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