MPG - Heater on/off whats the difference?

There will be no difference, you will get a bigger impact on MPG from wind direction, atmospherics pressure and a whole hot of other variables. Taking heat from the engine won't affect anything and the power use will be negligible. The opposite way round and there is some truth, in summer your better off using AC over having a window open, the drag increase outweighs the drag of the AC pump on the engine (I'm talking modern vehicle here, 1970's air con isn't exactly efficient)

Driving style must be the biggest factor! What is this Aircon,is it those flaps in the bulkhead??

Get yourself a Defender, no point worrying about the mouse farting on a candle that is the 'Heater', no worrying about whether opening the window will affect your 'Aerodynamics', just drive everywhere with a daft grin, not worrying (Much)

I think you will find speed verses wind drag will be the most consuming fuel factor stick between 50/ 60 mph you should be ok the higher the speed the more drag = more fuel
But towing a caravan you can't go over that speed so your within limits Theoretically.

Grimmer said:

Get yourself a Defender, no point worrying about the mouse farting on a candle that is the 'Heater', no worrying about whether opening the window will affect your 'Aerodynamics', just drive everywhere with a daft grin, not worrying (Much)

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Daft Grin... Its a grimmace as your ears take the pounding :clap2:

ER1C said:

Daft Grin... Its a grimmace as your ears take the pounding :clap2:

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What Can you speak up fella

Grimmer said:

Get yourself a Defender, no point worrying about the mouse farting on a candle that is the 'Heater', no worrying about whether opening the window will affect your 'Aerodynamics', just drive everywhere with a daft grin, not worrying (Much)

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+1

Not a genuine question surely?

andrew kennedy said:

I have a 2006 DT6 Sport. Can anyone explain what I could expect the increase in MPG to be if I were to not use the Heater/Ventilation system over say a journey of 100 miles of mixed urban/motorway use? and how exactly does using the Heater/Ventilation use more diesel. I will in the future be towing a light weight caravan if that makes any difference?

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Firstly I think if you are worrying about mpg then a land rover is not the best choice of transport
But as you asked
the heating will not change your mpg the A/C on larger engines also makes no odds things like open windows and tyre pressures will affect it more
A caravan will make a difference I can't speak for your land rover and caravan combo but my discovery will go from 19mpg down to 15mpg with my 1100KG caravan that's not that bad as any nice size tow car will not be far off the tow mpg to that
Example I had a BMW 530i that did 27mpg but would drop to 17mpg towing the caravan

+1 for no difference
+1 for if you want economy why choose a Landrover - in fact why a 4x4
-1 for get a Defender if mpg is an issue - their economy is poor because of the box ratio's (no I'm not anti Defender, for a working 4x4 it's a damn good choice - just not in winter and not without ear protection )

Makes not one jot of difference to the MPG, the engine has a lot of waste to get rid of and the heat taken in the car isn't done by altering water flow so the engine neither knows nor cares. The suggestion that the electric fan adds to a lack of economy is laughable, the ventilation fan in my cars is never off, always on low speed or auto.

The biggest gain you can get in MPG is in your right foot and your ability to be in an 'appropriate' gear - keeping the rpm in the torque / power generation 'sweet spot' that all engines have especially when towing. If your engine delivers the most useable power between 1500 and 2500 rpm then that is where you should keep the needle - smack in the middle of that zone. My TD5 is averaging 32mpg and I can still get 25mpg even with a 3+ ton twin axle box trailer.

As for the lightweight caravan if it is so light weight refer to 'why choose a landrover'