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as I trundled into work this morning behind a lorry with no throttle applied, I noticed the instantaneous mpg reading in my new (to me) car was showing as 99.9mpg
in the same situation in all the VAG group cars that I've previously owned, the same situation would show as 200 mpg.
all the mpg averages in the VAG cars i've owned previously have be ~10-20% over estimates compared to what you actually get at the pump. so far the subaru seems pretty accurate.
Have I discovered a new volkswagen misreporting scandal?
No, you've just discovered that cars report "I'm using naff-all fuel here" in different ways
which are then used in calculated an average.
and whats an easy way to skew an average?
iirc my car says --.- in the same situation, so my average would be fully broken! Alternatively, the average isn't just using the (usually pointless tbh) instantaneous read out
if i put the clutch down i get -.- which you would rightly leave out of an average.
if the engine is turning over but no throttle applied then it reports 99.9
but if you put the clutch down the car has to be using fuel to keep the engine turning. Sounds like Subaru are lying now - the bastards!
The instantaneous MPG reading is worked out on fuel used in the last second (or couple of seconds) whereas the average MPG for a journey is calculated using the fuel used since the start of the journey.
VAG trip computers don't reset until 2hrs (IIRC) after you've turned the engine off so if you head to the shops, wander round Sainsbury's for an hour and then head home, your average MPG is for both journeys.
all the mpg averages in the VAG cars i’ve owned previously have be ~10-20% over estimates compared to what you actually get at the pump. so far the subaru seems pretty accurate.
Have I discovered a new volkswagen misreporting scandal
My VAG goes to 200, then - -. The average per tank readout seems consistent with my manual calculations - but if they're really sneaky they'll have made it do an accurate readout when new and then switch to an optimistic map :). There are 3 average readouts available though - since last fill, long term, and this journey, obviously these all differ from one another.
My last car, a Ford, definitely lied - the trip computer was accurate for MPG average if you took a long journey, but it seemed to "ignore" all the extra fuel it chucked in when the engine was cold, so if you drove around town it was a massive liar.
My VAG goes to 200, then – -.
Mine too. 2011 Passat Bluemotion. My old Passat read about 1.5-2mpg than the actual fuel consumption (checked when refilling). I've not managed to get through a tank yet in this one so haven't compared.
Just a graph on ours (not VW), runs right upto the top with no throttle, and right to the bottom with throttle, funnily enough !
My instantaneous reading this a flippy needle, pedal down needle goes left pedal up needle goes right.
merc is the best I have used for accuracy.
Starts very low and then builds up as the engine warms. Seems pretty much bang on when I fill up and reset.
Has a bar graph on the Comand system (sat nav, radio etc) which shows your consumption every minute for the last 15 minutes. Oddly for a car with manufacturers figures that says it can do up to 61mpg the graph stops at 50 so when doing over 50 it just shows all full bars. If you can find a hill long enough to roll down for a minute then you get no bar at all as no fuel has been used.
I have a steep hill on the first 5 miles of my commute so I can just about get the car to mid 40's before it plummets when I go up the hill to low 30's and then I can get it back up to a mid to high 40's by the time I get to work.
all the mpg averages in the VAG cars i’ve owned previously have be ~10-20% over estimates compared to what you actually get at the pump
My Passat (2006) is so accurate I gave up calculating it manually as I always got the same number give or take a few tenths.
Mine does 300MPG in full electric mode, how’s that work?
And yes i gave up working it out myself as found it was so similar to the what the car reported it wasn’t worth me being so sad. Now I can check through an app what it does or bring it up the media screen.
My Passat (2006) is so accurate I gave up calculating it manually as I always got the same number give or take a few tenths.
Which engine, out of interest?
The 1.9 PD TDi (130) always gave me a reading that was pretty close to actual calculated - max of around 3% out but normally less.
The 2.0 TDi (140) in the current Ibiza is miles out. I struggle to get over 55mpg calculated out of it, but it regularly records 61-62mpg out of a tank & on a long, trundling journey the journey mpg can hit 77mpg.
Most I've had out of a tank from it is 520miles before thinking, bugger I better fill it up, which tallies with a calculated 55mpg much better than the supposed 620 miles I should be getting from a tank.
Which engine, out of interest?
Good question, it's one of the last PD engines, the 2.0 with the piezo injectors which eliminate the huge torque peak but is still noisy 🙂 Same car gets CR I think 2 years after mine from 2008 onwards. I wonder if CR technology makes it harder to calculate fuel injected for some reason.
Why does anyone calculate MPG at all? Surely you use car, it uses fuel, a light comes on, you buy more fuel.
Mine says 115 mpg before the dashes.
Instantaneous readout on my last car pretty much single handedly retrained my driving habits for the better. I reckon it saved me hundreds of quid over the course of 4 years; it’s one thing knowing that certain habits are more efficient, it’s quite another having them writ plain in front of your eyes.