Auxilliary Heater and Fuel Consumption -TDI

mjs4x4

A2OC Donor
I bought a 2002 TDI 75 a couple of months ago - and one thing I am not impressed with is fuel consumption. Mine struggles to average high 40's with a restrained driving style.

I recently used a 2004 Fabia TDI 75 (same AMF engine code) and found that on the same daily run the Fabia was 10+ mpg better than the A2.

I can't see any logic for this and wondered if the auxilliary heater in the A2 might be a contributory factor. What, in simple terms is the purpose of this? I also thought I read somewhere that from 2003 this heater was changed to a different type? Could this be a factor?

I should add that the A2 fuel consumption is with the Climate Control on Econ.

The only other difference is tyre size. My A2 is running on 17" wheels (soon to be changed to 16"). The Fabia runs 14" I think. I appreciate the wide wheels will add to the rolling resistance - but not to the tune of 10+ mpg.

One other point. I find that while both cars accelerate similarly, the accelerator pedal movement on the Audi seems to be about twice as far to achieve the same speed. Again, as both cars are 'drive by wire' I cannot think why this should be (and whether this might be a factor contributing to higher fuel consumption)?

Can any technical brains greater than mine (not difficult) suggest why the same engine in a steel bodied Fabia is so much more economical than an Aluminium A2?

Mike
 
Hi MJS4x4,

I started a thread under the fuels forum to record what sort of MPG I achieve. I'm hoping a few members will join in. It would be good to compare across the various models.

http://www.a2oc.net/forum/showthread.php?t=4841

If you get a chance to have a look, you will see that so far my MPG varies quite a bit. I intend to keep it up to date, as I fill up with fuel, so have a look from time to time.

From my own experience, my A2 1.4 TDI can return low 30 MPG around town, in stop start traffic and doing short journeys. My guess is that you were doing similar journeys.

Do you know how the weight of the Fabia compares with an A2 TDI? I could not find the weight on the Skoda web site. I also saw 70 and 80 BHP 1.4 TDI engines, but no 75???

John.
 
At a guess I'd say yours possibly has the webasto heater which runs on diesel so will use more in colder weather, Skipton01 would be able to confirm if you passed him more details on your car.
I found that by following Audis own handbook advise i.e. 1st gear for the length of the car then change up at 2k rpm makes quite a difference, as to your comments on the tyres what make have you got on? I found a difference of 5mpg between bridgestone & vredestein of the same 205 section.
I also found that my A2 was more economical round town than on a run! which really puzzled me until I found a 10mph increase in speed over 60mph = a 10 mpg lass in economy! I dread to think what a 90mph run would do! All down to aerodynamics I am afraid, it takes more effort to throw a basketball than a football!
 
If you've got the ECON button on, the Aux Heater will be switched off. Mind you it only fires up if the outside temperature drops below about 6 degrees, anyway.

We find it does knock 2-4 mpg off the consumption on our TDI75. However, with some longer journeys, mid-high 50's are regularly seen.
 
I dont think our TDI engines are the most modern on the block! The Fiat engines do seem to be top performers.
 
Poor_John said:
Hi MJS4x4,

From my own experience, my A2 1.4 TDI can return low 30 MPG around town, in stop start traffic and doing short journeys. My guess is that you were doing similar journeys.

John.
That's the lowest figure I ever seen quoted for a TDI A2! We've never got ours below 47mpg - in the winter with the Auxiliary Heater going the whole journey from home to work (7 miles, half in town)....
 
How can you tell if you've got an auxillory heater?
I've seen a noticable increase in fuel consumption recently. It normally returns 54mpg in mixed driving, but this has now dropped to just over 50mpg!!
It might be a poor batch of fuel - will have to keep an eye on it
 
SimonT said:
How can you tell if you've got an auxillory heater?
I've seen a noticable increase in fuel consumption recently. It normally returns 54mpg in mixed driving, but this has now dropped to just over 50mpg!!
It might be a poor batch of fuel - will have to keep an eye on it
I think all the diesels have them. Early cars a diesel burning type, later ones electric. With our early one, you can hear it from the outside if you stop the engine while it's working - sounds like a fan heater slowing down. Without it the car takes 7-10 miles to warm up!
 
A couple of further points on this in response to comments received.

The weight of the two cars is actually the same - the 'mass in service' stated on my A2 reg. doc is 1228kg - the Fabia is 1222kg. I guess all the extras on the A2 cancel out the weight savings with the Aluminium body!

My average MPG in the A2 of 46/47 mpg is not a reflection of either town driving or a lot of 70 mph+ driving - it contains a lot of 'diesel friendly' steady 40/60 mph motoring.

I agree that the 4 cylinder VW Group diesels are often as or more economical than the 3 cylinder TDI's and I attribute that to them being pretty understressed in average driving and running very low RPM.

What gets me is why this damn Fabia - (which IS the identical 75bhp engine - not the newer 70 or 80 bhp engine) - is so much more economical than the A2? I've driven it again today and averaged 65mpg on the run to work - the fuel guage never seems to move!

I am wondering if the fact that I seem to have to push the pedal much further in the A2 to achieve the same speeds is the key? Maybe the injectors just have to squirt more fuel in to achieve the same result?


Mike
 
I normally average 60 mpg 58-63 of mixed driving with a/c on all the time. Driving round town on short journeys makes little difference bringing it down to mid 50's. The highest I ever recorded in my 2001 was 74.3
 
mjs4x4 said:
I've driven it again today and averaged 65mpg on the run to work - the fuel guage never seems to move!

Are you reporting what the computer in each car calculates as average? I would take the readings as a guide only.

I would argue the speed that the fuel guage moves is related to the size of the fuel tank. I'm not sure that the two tanks are the same size, but I can understand if a car with a smaller tank is more likely to seem to drink fuel more quickly as the tank drains quicker.

John
 
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