50mpg from 1.4TDI90 on long trip - normal?

mathatcat

Member
to me 50mpg seems low - when I first got mine it was doing just above 50 (not sure what now the weather has changed) and I found out that the fuel cooler under the car was leaking (through the metal), so as I drove v small drops of fuel would drip on the road / it was not that obvious - now that it's fix I get about 60mpg which still does not seem that good as I get 45mpg out of my big 5 series BMW (2002 2.5L )
 

RAB

Technical Specialist 1.2 TDI
dan_b;172524St said:
4. Switch off air-con until engine is up to 90.

Dan,

Not as effective as you might, although I can see why you made the point. The sensor is external to the head and so you are not looking at the block temperature, which is why it takes so long to get up to temperature. You won't get any heating from the coolant and any effect on the displayed coolant temperature until the thermostat opens. If you switch the heating/air con off completely you will see that the 90 deg C mark is reached more quickly under the same conditions, but only because the heating is taking heat from the coolant external to the block. If you leave the heating on, on AUTO the fan doesn't speed up until the coolant gets up to temperature. So switching off the heating doesn't make much difference, if any.

RAB
 
I can vouch for the temp sender and thermostat replacement on fuel economy.

My second tank of fuel was during a replacement of the Temp Sender and Thermostat. I stupidly used aftermarket parts from eBay which did not fit properly or work correctly.
The temp gauge was erratic and the car never seemed to get to temp. The first tank I recorded only got 40mpg. Though this is not recorded on Fuelly.

The second tank of fuel was after a fair amount of brakes and suspension work had been done inc 4 wheel alignment. I also tried a lot of things suggested in this thread. Tyre pressures etc.

Our car had three people in it and bags driving to France for Christmas.
The second tank of fuel was also hampered by a 7 hour journey to Dover in the worst weather possible and a 200 mile journey, French side, to our destination in the same kind of weather with further traffic jams.

The third tank was 69.9mpg, much much better. The journey back through France was dry and sunny for the most part, no wind and no traffic jams.
We had four stops for bathroom breaks and had to hard accelerate a couple of times UK side to avoid some trucks who decided to pull out on us for no reason.
Note to self, I must get a louder two tone horn for the car.

I kept a steady 65mph at 2200rpm. I have 15" competition wheels.

I hope this helps.
 
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dj_efk

A2OC Donor
I was researching older TDI90 fuel economy threads as I was surprised by Merlin not easily achieving 65+mpg on my longer trips recently. I came across this one which I found pretty helpful, also This thread on another forum by a former member Mike Mars (why is he no longer on here anyway? Shame!).

Bumping as I thought they would make similarly interesting reading to others
 

Malcyb

Member
I’ve been scrupulously recording my economy (got an unmodified TDI90) in the past 9 months and it’s averaging 53 in mixed driving, not many very long runs. I was slightly disappointed by this as I always drive with an eye on economy, however my dad owned this car for the first 30k miles of its life and he’s similarly careful/nerdy in this respect - he didn’t average any better, so I’ve got to assume this is in line with expectation. I managed to get low 60s out of one real economy run. I had thermostat and temperature sender replaced as the temperature was never getting up to 90; though this fixed that fault I didn’t notice any improvement in economy.
 

Edwrai

Member
My 90 averages 65 to the tank it’s hard not to get over 60 to the tank, the best it’s done to the tank was 78mpg I have owned a 75 and it couldn’t achieve the same mpg. The rear readings on my DIs were way off!


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Malcyb

Member
My 90 averages 65 to the tank it’s hard not to get over 60 to the tank, the best it’s done to the tank was 78mpg I have owned a 75 and it couldn’t achieve the same mpg. The rear readings on my DIs were way off!


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very impressive! There’s no way in a million years I’d be able to average that, though my one real concession to uneconomic driving is that I rarely turn the aircon off... but my figures don’t seem to suggest that my car is in poor condition. My DIS readings are a tad lower than reality.
 

Edwrai

Member
very impressive! There’s no way in a million years I’d be able to average that, though my one real concession to uneconomic driving is that I rarely turn the aircon off... but my figures don’t seem to suggest that my car is in poor condition. My DIS readings are a tad lower than reality.

My DIS readings are hugely out and really under reports.

Depends on how and where you are driving. I don’t see much traffic


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A2Z

A2OC Donor
My 90 averages 65 to the tank it’s hard not to get over 60 to the tank, the best it’s done to the tank was 78mpg I have owned a 75 and it couldn’t achieve the same mpg. The rear readings on my DIs were way off!


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Although Audi quoted similar mpg figures for both the TDI 75 and 90 variants in the real world and having owned numerous 75's and a couple of 90's the difference in mpg is huge BUT in favour of the 75 like 99.9% of people who have owned them will agree and by around 8-10 mpg from my experience.

To average 78mpg in either of my 90's i would have needed to be going downhill with the clutch depressed 😂

Mpg in the 50's is pretty much the norm for a 90 and 60's for a 75.

These figures are obviously dependant on everything being in tip top order and working as they should. No binding rear brakes, under pressure tyres and faulty temp sender/thermostats👍
 

Howey

Member
Whats the expectation time/distance for reaching 90 degrees? Imagine air temp and load placed on engine will be very important!
Paper work shows the PO fitted a euro special circoili stat which seems to be working fine but not sure, have other 1.9 pd tdis thou?
 

Malcyb

Member
Whats the expectation time/distance for reaching 90 degrees? Imagine air temp and load placed on engine will be very important!
Paper work shows the PO fitted a euro special circoili stat which seems to be working fine but not sure, have other 1.9 pd tdis thou?

Since replacing thermostat and temperature sender, mine always reaches 90 within 10 miles or so and stays there on any kind of journey. Prior to that it would never get over 70.
 

dj_efk

A2OC Donor
My 90 averages 65 to the tank it’s hard not to get over 60 to the tank, the best it’s done to the tank was 78mpg I have owned a 75 and it couldn’t achieve the same mpg. The rear readings on my DIs were way off!


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Ed what cruising speed do you do? This seems to have been the missing key info in most posts where others have reported what they’re getting.

I was expecting 65+mpg from a 70mph cruising speed. This equates to 2000rpm in sixth with the PTW box, as it more or less would in your MYP.
 

RAB

Technical Specialist 1.2 TDI
A simple check for the coolant sender (actually it's two senders) is to compare the hot coolant temperature in the Engine section of VCDS with that in 17 Instruments. They should be the same. If the engine or instrument sender is reading low, they will produce higher actual or calculated fuel consumption, respectively. You should know what the actual fuel consumption is, so you should be able to work out which is reading incorrectly. In short, if the indicated temperatures are different, change the sender.

RAB
 

Howey

Member
A simple check for the coolant sender (actually it's two senders) is to compare the hot coolant temperature in the Engine section of VCDS with that in 17 Instruments. They should be the same. If the engine or instrument sender is reading low, they will produce higher actual or calculated fuel consumption, respectively. You should know what the actual fuel consumption is, so you should be able to work out which is reading incorrectly. In short, if the indicated temperatures are different, change the sender.

RAB
Great info!
Yes i have fitted a Beru sensor after the dash reading side failed
 

timmus

A2OC Donor
A simple check for the coolant sender (actually it's two senders) is to compare the hot coolant temperature in the Engine section of VCDS with that in 17 Instruments. They should be the same. If the engine or instrument sender is reading low, they will produce higher actual or calculated fuel consumption, respectively. You should know what the actual fuel consumption is, so you should be able to work out which is reading incorrectly. In short, if the indicated temperatures are different, change the sender.

RAB
Absolutely. Any discrepancy between the two coolant temperature sensors won't trigger a fault code. Even if the thermostat is opening at the correct temperature and the gauge in the instrument cluster is showing the correct reading, the ECU can still believe that the car isn't yet at full operating temperature, meaning excessive fuel is injected. Colour DIS has a page for comparing the readings from the two temperature sensors, making the diagnostic process easy, despite the lack of fault codes.

Aerodynamic drag increases with the square of speed. Double your speed, and you quadruple the aerodynamic drag. Consequently, the difference in fuel consumption between 60mph and 70mph is, proportionally, quite large. Nevertheless, I'd be disappointed not to exceed 60mpg at 70mph, even with the standard 5-speed gearbox.
I usually cruise on the motorway at a true 62mph, in 6th gear, and average about 75mpg. Of course, at this time of year, that figure is somewhat reduced. Cold air is denser, meaning greater aerodynamic drag.

Cheers,

Tom
 

Seb_Gurkyh

Member
While it says you're running a remap and 6-speed-gearbox, I'd at least like to point out my own struggles with fuel consumption in a recently purchased TDI90.

People call me driving like a retiree and I'm not even 30 :p

My daily commute is about 55 miles overall (2-way), of which 37 are spent at 50-56 mph on A level roads and fairly broken motorway. I never exceed 56mph (90 kph).
Since the terrain is quite mountainous, on the way back I take a 13 mile long "shortcut" alongside the motorway that is a mixture of downhill coasting, 30mph rural towns and some 45mph inclines. Corners are taken at the highest, safely possible or permitted speed to not have to use brakes.

Using my 1.4 BBY for this route has put me in the top 3 of Spritmonitor fuel economy figures with an average over 2020's summer season of 59.8 mpg/4.72l/100km (on 205/40R17 and heavy wheels [Sline+2kg per corner]). Extras on the car are foglights, climate control and rear speakers, rear seats are left at home.

Using a TDI 90 on Sline wheels with above extras + OSS + 2x sports leather on OEM 17" wheels, I have just about managed to do the route on 67 mpg/4.21 l/100km. This just about puts me in the top 10 on spritmonitor, though at 30% the sample size of TDI90s vs 75hp petrols.

Mind that at least for me, DIS isn't really that accurate - the TDI90's actually overreads with 4.4 on the display when it's 4.2 at the pump. (So would show less mpg than actual on a UK model) On all other cars I've driven, it was the other way round with the car being much more optimistic than the pump.

On 175 winter tyres and fueling up with ARAL/BP Ultimate Diesel, I have managed to get the consumption as low as 74 mpg, but that takes an extreme effort in eco-driving and pretty much no use of the turbo boost.


Overall I, too, was a bit disappointed by the TDI90's consumption figures, especially considering that the average values on aforementioned site are not too different from each other, contrary to what is being reported on A2 specifc sites at 58 mpg for TDI75 vs. 57 mpg for TDI90s.

The only thing that I have not been able to proof myself is how much influence extras have - leather alone, at least on the rear seats, is only a 2kg difference, though I assume OSS will be quite the difference.


For a conclusion though: Yeah the TDI90 appears to use quite a bit more than a TDI75 and possibly not a whole lot less than an "empty" petrol, but the ability to "boost around" kinda makes up for it. (Though I will admit I have never driven a remapped A2 - bit of an expensive endeavour to get that TÜVed around here)
 

Edwrai

Member
Ed what cruising speed do you do? This seems to have been the missing key info in most posts where others have reported what they’re getting.

I was expecting 65+mpg from a 70mph cruising speed. This equates to 2000rpm in sixth with the PTW box, as it more or less would in your MYP.

You won’t get 65mog at 70mph maybe 60ish to get this figure.


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