I have a MAN 18.290 4x4 converted to a motorhome in Australia. Gross weight is a fairly constant 12t. It has recently had a valve reset. Fuel consumption dropped to around 23l/100k for the first 500klms, but has now climbed back up to the previous level of 27-28ltrs/100 klm (bitumen) at around 90-95kph.
Also, when the temperature drops to around 10 degrees, as it has now for winter, that increases to over 30ltrs /100k.
MAN dealer has no idea where to start. One a really cold day last year, fuel consumption increased to 34l/100k.
Have mates with similar trucks and their fuel consumption is around 23ltrs/ 100k.
How it’s driven is usually the main factor. I can easily bump up 20% in the amount of fuel I used if I change how I drive to a more aggressive style. By that I don’t mean road rage but taking it further up the revs before changing gear, harder acceleration, driving under power approaching junctions, roundabouts, traffic lights, queues of traffic instead of using engine braking from further back…
Don’t know if Australia has a winter fuel mix for diesel like we do here in the UK but if it does around 10% higher fuel consumption is normal due to the increased amount of kerosine they put in to stop the diesel waxing in cold temperatures.
It’s surprising when you put your mind to it just how far you can travel with your foot off the throttle pedal, ideally you should only need to use the brakes to bring the vehicle to a final halt, braking from speed means fuel wastage, and make use of terrain whenever possible ie allow the vehicle to gain and maintain whenever possible downhill with no or minimal throttle, and to lose speed naturally on uphill sections that you might approach that bit faster in order to stay in top gear.
Also remember any speed above 80kms you’re shifting a lot of air, how does your aerodynamics compare to other similar vehicles, tyre pressures and tyre type?
I found with MAN’s especially is that whilst they are a free and high revving that by forcing by use of gears the engine to stay in the 1000/1500 rev range the engine would give more torque, leading to better journey times and lower fuel usage.
Noticeably after i’d had a weeks holiday where the vehicle had been driven harshly in full auto that it wouldn’t pull your hat off but after an hour or so driving in manual making it work in the correct rev range again it would come back on song.
Is it getting enough fuel so it can be driven in the peak torque band, does it need a tweak so allow better progress at lower revs?
I wouldn’t be bothering with the MAN dealer, a good old school Diesel shop is what you need for any fine tuning.
Juddian:
I found with MAN’s especially is that whilst they are a free and high revving that by forcing by use of gears the engine to stay in the 1000/1500 rev range the engine would give more torque, leading to better journey times and lower fuel usage.
Thanks for that i had a discustion with someone that should know a lot better about that very thing. he was insistant that i should never change gear when the engine was struggeling to the point you were nearly knocking hell out the bigends and shells he was aderment that mercedies knew what they were doing and if it needed to drop a cog or two it would.
it ended with me trying to explain the basics of engine managment and how it avoids damage to the engine by retarding the ignition and all he said was "yes well mercedies will know that"i gave up at that point
cooper1203:
Thanks for that i had a discustion with someone that should know a lot better about that very thing. he was insistant that i should never change gear when the engine was struggeling to the point you were nearly knocking hell out the bigends and shells he was aderment that mercedies knew what they were doing and if it needed to drop a cog or two it would.
For pretty much every lorry I’ve driven for the last 20 years they have a green band, yellow and red. Keep it in the green and it’ll give the best economy. In the yellow and red you’re just turning diesel into smoke. The lorries I drive, like virtually every lorry in the UK is an automatic, the green band goes all the way down to 800RPM and they won’t change down gear until they’re below 1000 RPM and they’ll change up a gear when it’ll drop the revs down to 1000 when you’ve changed up. Most of the torque is generated at the bottom end of the rev range and that’s what you need to keep the wheels turning. The most economical is where you’re in the rev range putting the most load on the engine which is at lower revs.
On the MAN you have a green band but there’s a portion of it which is a much more prominent green than the rest and it’ll move up and down depending on what you’re doing. Keeping the revs within this range is the absolute most economical. The dash below is from the same model as yours. It suggests you want to be keeping within 1100-2300RPM, ideally between 1300-1500 when cruising.
