Open Road vs Town Drivng Diesel Consumption

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Family_Dog
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Open Road vs Town Drivng Diesel Consumption

Post by Family_Dog »

Is this true? Got this from the LCCSA forum...
so is it generally true that diesel consumption is worse on the highway than in town?
Yes...2H diesel 12.2l/100km avg in town driving compared to 13.6l/100km avg when doing constant 115kph (true speed) unladen on a near flat road.
I would have expected consumption on the open road to be better?

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Re: Open Road vs Town Drivng Diesel Consumption

Post by Niel »

When these guys give these consumption figures do they factor in the roof rack.....with x, y and z on top of the roof..... ? With the wind resistant factor really coming into play at around 110 km/h they will have worse consumption on the open road than in slower town driving. I have seen with my Isuzu (Diesel) that I get better consumption in town than on the high way. With the KZ, I stopped keeping record (don't do long trips at the moment).
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Re: Open Road vs Town Drivng Diesel Consumption

Post by Family_Dog »

Reading a bitfurther down the thread, one guy mentioned his consumption had improved and he got excellent figures with a fully laden LC70 including roofrack and gear on the roof.

Thumbs up, so far!

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Re: Open Road vs Town Drivng Diesel Consumption

Post by iHilux »

I've heard these claims too. I can't substantiate them, as I could never measure my economy over the two situations.

Food for thought though.

Around town, in a diesel you rarely ever using more than 2000rpm. Diesel consumption is directly related to rpm. On the open road however, you travel in a 2500 - 3000rpm band. This could be one of the possible explanations.

IOW, if you traveled on the open road say for 100km at 2000rpm, your diesel fuel consuption would be less than doing the same distance at say 3000rpm.

Possible another factor to consider...... and I might add that this is pretty much hear say.

On a petrol engine, if you labour the engine, and push your foot flat, the amount of fuel increase to that of an open throttle, even though your engine doesn't respond immeadatly. All excess unburt fuel get passed through the exhast system and is wasted. Only once the revs increase with the amount of unburnt (wasted) fuel decrease.

With a diesel on the other hand. If you pump is set correctly, the amoung of fuel used is relative to the engine rpm rather than how flat you foot is.

This is a very simple explaination, and obviously differs from brands and circumstances.

Can this explain why in town, petrol engines are are often heavier than on the open road? (the amount of unburnt fuel by the constant acceleration)
Can this also explain why petrol engines are hevier when towing? (the amount of unburnt fuel by accelerating more than the enigine is burning)

My 2cents worth, but will be watching this thread with great enthusiasm. What do the pro's say?
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Re: Open Road vs Town Drivng Diesel Consumption

Post by xuliH »

It might be driving style related, but I get much better diesel consumption in town than on the open road.

And there is a big difference in consumption between 110km/h and 130km/h. I agree with iHilux that engine revolutions make the difference.
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Re: Open Road vs Town Drivng Diesel Consumption

Post by Niel »

quote="xuliH"]engine revolutions make the difference[/quote]
I agree. My 2.7 was heavy on fuel if over 3000 rpm (abought 120km/h) but this motor like being revved before you got the power. I assume that is why the 2.7 VVTI motor is a bit lighter on juice that the older 2.7's.
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Re: Open Road vs Town Drivng Diesel Consumption

Post by Family_Dog »

Riaan has subsequently posted this statement:
My first 5k was not so hot (but still better than expected), but the last few tanks have been awesome, even this weekend doing 140+ on the open road with family and weekend gear I got 12l/100 exactly. So I guess it does improve over time and as the mechanics runs in?
http://www.landcruiserclub.co.za/cms/in ... &start=750

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Re: Open Road vs Town Drivng Diesel Consumption

Post by Family_Dog »

And Hans Richter has this to say...
have just come back from our first trip with our new 70 SW to namibia.We,especially my wife liked the performance very much.
Our consumption was:
15-17l/100km @ 120-140km/h
14-15l/100km @ 110-120km/h
11-12l/100km on gravel up to 100km/h
10-11l/100km in town
Can anybody share their experience please.
http://www.landcruiserclub.co.za/cms/in ... &start=746


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Re: Open Road vs Town Drivng Diesel Consumption

Post by pietpetoors »

I think wind resistance might be the cause of this phenomenon.
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