50mpg from 1.4TDI90 on long trip - normal?

Hippo

Member
Just throwing in my twopence worth, in these £££ fuel days, as the lucky owner of two cherished Tdi 90's that get oil changes every 3k miles etc.. As it happens, I have calibrated the DIS-reported fuel consumption to almost 100% accuracy (unsurprising as practically all of my driving is open road). Both cars, incidentally, are running 16" 205 section tyres and have been mapped. No two production units are identical. But they are within, like for like, about 2 MPG of each other. On long motorway runs at up to c. 65 MPH, typical consumption is 6o - 64 MPG (assuming no head winds, restrained accelleration, not heavily loaded). Experimantally, I have tested on a polar bear saving c. 55 MPH long run and, yes, 70 (and better) MPG is entirely possible. So, relative to earlier forum disbeliever observations, 3 pots with a VVT turbo can deliver the efficiency goods too! BUT, the wind-tunnel efficiency loses its lustre pushing over 70 MPH. In summary, Tdi 90's driven with a bit of fun and zest actually and should return 55+ MPG - from years of real-life experience. Not wishing to open/ add to any conroversy, but just stating it as it is.
 

dj_efk

A2OC Donor
Just throwing in my twopence worth, in these £££ fuel days, as the lucky owner of two cherished Tdi 90's that get oil changes every 3k miles etc.. As it happens, I have calibrated the DIS-reported fuel consumption to almost 100% accuracy (unsurprising as practically all of my driving is open road). Both cars, incidentally, are running 16" 205 section tyres and have been mapped. No two production units are identical. But they are within, like for like, about 2 MPG of each other. On long motorway runs at up to c. 65 MPH, typical consumption is 6o - 64 MPG (assuming no head winds, restrained accelleration, not heavily loaded). Experimantally, I have tested on a polar bear saving c. 55 MPH long run and, yes, 70 (and better) MPG is entirely possible. So, relative to earlier forum disbeliever observations, 3 pots with a VVT turbo can deliver the efficiency goods too! BUT, the wind-tunnel efficiency loses its lustre pushing over 70 MPH. In summary, Tdi 90's driven with a bit of fun and zest actually and should return 55+ MPG - from years of real-life experience. Not wishing to open/ add to any conroversy, but just stating it as it is.
I think for most people, this is the answer to the question that heads this thread, summed up in one post. Case closed!
 

depronman

Member
Yebbut slipstreaming and hypermiling do tend to prolong the journey...

So does pushing the A2. Though I recommend removing the engine and box as it makes it a lot lighter. You may even convince dvla that you no longer need to pay road tax (but I doubt it)

Paul


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pc759

Member
Same issue with mine some time ago
tried absolutely everything bar temp sender
ended up taking it to that diesel tuners in barnsley can’t remember bed name but we’ll known paid them two hours to diagnose
they said timing was out and reset that now I can get 62 with extra urban driving to work, still not great but better
I’d had a stealth remap many years ago but now don’t know if all those ponies are still there anymore. Anyway it’s old and I like it how it is now
 
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
Hi Tom, where can I find this page on my colour DIS? For comparing the two readings please? Thanks 😁
 

timmus

A2OC Donor
Hi Tom, where can I find this page on my colour DIS? For comparing the two readings please? Thanks 😁
Hi Gary,

I don’t have Colour DIS in my own A2, so have not committed the menu layout to memory, but I believe it’s under ‘Measurements > Summary’.
One is labelled as Coolant Temp (E) and the other is labelled as Coolant Temp (D).
E = engine, D = dash (instrument cluster).

Cheers,

Tom
 
Hi Gary,

I don’t have Colour DIS in my own A2, so have not committed the menu layout to memory, but I believe it’s under ‘Measurements > Summary’.
One is labelled as Coolant Temp (E) and the other is labelled as Coolant Temp (D).
E = engine, D = dash (instrument cluster).

Cheers,

Tom
Thanks Tom, I will have a look tomorrow, I too am looking into a lower than expected mpg issue 👍🏻
 
I checked this morning,
There's a 5oc discrepancy, engine is reading 5oc cooler than the dash,
But a bigger concern is that on a cold 6oc morning, the engine was only upto 75oc in a 10 mile (very leisurely) 50 mph commute?
It has had a new OEM thermostat 20k ago,
And I'm seeing low mpg on my half urban half open road commute (around 45 mpg)
Tyres are pumped upto 38psi
Wheels are 17s
 

dj_efk

A2OC Donor
Well I would suggest that if you have differing readings for temperature then your dual-circuit sensor could do with replacing - but only if you are experiencing less than optimum economy figures; otherwise I'd leave well alone.

EDIT - I checked on my own car using CDIS and I have a 2 degree variance. Make of that what you will.
 
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