Thread: Towing with an 8 speed D4.

I have just come back from a 10K trip, and must say that I did not have any problems towing a 2400kg van. But what did alarm me was the lousy fuel economy. On towing sitting on real speed via gps of 95khp, I did not get better than 16 lp100km. Mostly it was around 18. This is real NOT what the Disco tells me which is about 2litres less than actual. Friend who had an Isuzu MUX towing the same weight and speed got consistently 3 litres better than me. As a tow mule the D4 is lovely but when you have to fill up every 300kms is is expensive compared to others. At first I thought perhaps needed a service (it was due) but after service no improvement at all. All filters were replaced and I have a snorkel fitted.

OK to add to this we have just completed a 7000km trip from Caloundra where we picked up our AOR Q+ (2500kg) to currently Alice Springs having towed it across and along the Great Dividing Range, Sandstone Ranges in Central Qld and across the Barkley Tablelands. The majority of terrain has not been flat until we hit the Stuart Highway a couple of days back.

We took the opportunity to do a lot of experimenting with D and S with the end result being S and cruise control and let the car do the work as it is smarter. D in hilly terrain resulted in overloading the engine and transmission as it wanted to hold higher gears followed by hunting as it jumped up and down far too quickly ascending and descending even small changes in the road level. S on the other hand gives us fast changes for overtaking and it does that superbly as well as holding top gear much longer. We tend to see it in 7 0r 8 most of the time and the changes are imperceptible so I have no idea if I am right on that or not. As well at 112kph we are sitting on 1800RPM and averaging 17l per 100km. On long climbs it will change to 2000RPM or slightly more but holds gear well and is relentless in performance. If we have to battle galeforce headwinds when we still sitting on 1800RPM but we go to averaging 19.7l per 100km or slightly more. Temperature gauge did not move.

I am a touch flabbergasted at towing and dropping as low as 1200RPM unless going down hill. Nothing wrong with giving these things a bit of a rev. A few times we simply "resumed" after leaving a low speed limit area and it was impressive how quickly the car returned to cruising speed after swinging up to slightly over 4000RPM on some of the changes. Nothing dramatic at all just a smooth application of power. We also have our normal touring kit on the roof consisting of, spare wheel and tyre, space case, 3xJC so that is worth around 2.3l per 100km in our testing just through wind resistance. This sits on a Rhino wire mesh platform and 3x aero bars.

As well the above is done on cruise control unless in really hilly country. The car does it brilliantly and remains considerably more fuel efficient than any LC200 I know of towing the same or similar weights

Rob

Originally Posted by Graeme

Special edition power version....


My 230KW 8-speed 4.4 with a slightly higher final drive ratio suffers from the same problems when it happily gets down to 1000 rpm with 2.5T behind until a slight incline.

Haha, thanks Graeme.... wouldn't that be nice to have! It was a bit late(or was it early?) when posted this up.

Thanks Sean for the graphs above. Seeing them makes sense with regard to the gear changes in my situation. When towing, I always watch "stuff" on the GAPII. One of the items I watch is "Gear Commanded". When in Sport Mode, Cruise Control, 8th gear, 100kmh & you pull the down shift paddle once, the gearbox goes from 8th to 6th, never to 7th. This is straight into the max torque at around 2400rpm but not where the max kW are. To get max kW, you have to drop to 5th gear but the torque drops off slightly. I sometimes watch the "Torque" too. If left to its own devices, the box will change fro 8th to 7th & then to 6th if necessary.

As mentioned earlier, fuel consumption is around the 18l/100 mark or 100km per quarter tank on the gauge. At 300km one needs to be looking for fuel. Also when using the Resume button on the Cruise Control, the car seems to accelerate better than by doing it the old fashioned way with the accelerator pedal. I'm worried I'm going to wear out the Cruise Control Buttons.

In a D4 how does the vehicle get down to 1200rpm under load - like towing. In drive it will automatically change down, in sport it will automatically change down and if in Command Shift, if the load perameters get out of spec for the selected gear it will change gear anyway.

So if the gearbox was in drive and got down to 1200rpm under load then the engine/gearbox was happy and the load was within the specs for the situation.

An auto of all types changes gear based on load and throttle position (to oversimplify) so if towing in Drive the car will always select the right gear for the load - higher the load the lower the gear, the lower the load the higher the gear (again to over simplify). Issues mainly arise when the load fluctuates around the spot the gearbox will change gears - so a lot of ups and downs -sometimes Sport helps here and even Command shift.

On generally flat roads I just use Drive and even cruise - and in hilly I use Drive Sport and no cruise. I would normally only use Command Shift if towing offroad or going down steep hills where I need to hold a lower gear.

Garry