On board trip computer/av mpg indicator
Discussion
Whilst on the subject of fuel economy, has anyone noticed a disparity between what the onboard computer reckons and the real life mpg? I've done several tests and am getting consistently higher reported average mpg from the in car computer compared to the real life figure I'm actually getting.
Example (just in case anyone can see a flaw in my test methods
Fill her up to the brim, reset the av mpg and trip counters and drive around as normal until just approaching the red low fuel level. Return to garage and refill and note the litres it took to refill, the current tripped mileage since the reset and the current indicated av mpg from the comp.
Doing the sums:
no. of litres it took to refill/4.55=gallons used
Tripped mileage/gallons used=av mpg
No matter how many times I do this I get figures between 13-16 mpg from above calcs yet the computer constantly reports figures between 21-24.
Anyone any ideas?
Example (just in case anyone can see a flaw in my test methods
Fill her up to the brim, reset the av mpg and trip counters and drive around as normal until just approaching the red low fuel level. Return to garage and refill and note the litres it took to refill, the current tripped mileage since the reset and the current indicated av mpg from the comp. Doing the sums:
no. of litres it took to refill/4.55=gallons used
Tripped mileage/gallons used=av mpg
No matter how many times I do this I get figures between 13-16 mpg from above calcs yet the computer constantly reports figures between 21-24.
Anyone any ideas?
My worst readinsg are when I am standing still - can practically watch the gauge go down with the naked eye!!
Does anyone else notice that as soon as the needle gets near the red line it plummmets at a rate of knots. The dist to empty reading seems to accelerate once I get near a 100 miles remaining - weird.
Bit like an Audi I had trip said 250 miles left when finished at the end of the day - get in teh following day it would say 50....
Bring back good ole days needle and orange light guaranteeing another 30 miles.
Does anyone else notice that as soon as the needle gets near the red line it plummmets at a rate of knots. The dist to empty reading seems to accelerate once I get near a 100 miles remaining - weird.
Bit like an Audi I had trip said 250 miles left when finished at the end of the day - get in teh following day it would say 50....
Bring back good ole days needle and orange light guaranteeing another 30 miles.
FinallyVXRed said:
No matter how many times I do this I get figures between 13-16 mpg from above calcs yet the computer constantly reports figures between 21-24.
Anyone any ideas?
Anyone any ideas?
Hmm I initially thought that the trip computer might be measuring US Gals instead of Imperial Gals but as US Gals are Smaller the difference would be the other way round. I.E Would have used more fuel for the same distance and would have reported a lower MPG then reality
Oh well was a good theory while it lasted.
Well_Fans said:
hole in the fuel tank? Neighbour sneaking out to your car at night with a siphon hose? Dodgy petrol station owner with meters altered to say you're putting in more fuel than you really are?
no checked for the first, could be the second but he seems a nice geezer so I hope not and can you open the filler cap cover from outside without damaging it? As for the 3rd.... mmmm I use the same sstation so you may be onto something there....I'll try another and repeat the test Demolition Man said:
Go and have a lie down in a darkened room? 
was it that stupid a question then 
silentmonkey said:
Hmm I initially thought that the trip computer might be measuring US Gals instead of Imperial Gals but as US Gals are Smaller the difference would be the other way round. I.E Would have used more fuel for the same distance and would have reported a lower MPG then reality
Oh well was a good theory while it lasted.
Oh well was a good theory while it lasted.
I did wonder if it was displaying Mpg but reporting Kpg but discounted that as I thought someone else would have noticed if they all did that
FinallyVXRed said:
No matter how many times I do this I get figures between 13-16 mpg from above calcs yet the computer constantly reports figures between 21-24.
I think the computer probably gets a bit embarrassed and fibs a bit as a result...
In truth I always scroll through that particular page as it tends to make me wince.
The 2004 VXR is definately more thirsty than a 2004 CV8 BTW. I think its the shorter gearing which makes it noticeably quicker but .....
Bennno
Well 6.0 actually but just for the record this isn't a moan about fuel economy in the slightest, if I was bovvered (face etc) I definitely wouldn't be driving a Monaro!
I just noticed there was a definite disparity between real life and what the onboard comp felt was going on after filling up one day. The trip told me I had 340 miles left before empty and then after only 170 miles it started crying about low fuel telling me I had only 40 miles left.
I just wondered why and did some tests and found it consistently told porkies
but just for the record this isn't a moan about fuel economy in the slightest, if I was bovvered (face etc) I definitely wouldn't be driving a Monaro! I just noticed there was a definite disparity between real life and what the onboard comp felt was going on after filling up one day. The trip told me I had 340 miles left before empty and then after only 170 miles it started crying about low fuel telling me I had only 40 miles left.
I just wondered why and did some tests and found it consistently told porkies
I do a 320 mile round trip at least once a week and all high speed motorway driving. I tend to put in about 57 litres of Optimax and that is enough to get me back to the next refill. I calculated it at 24.something mpg (is this correct?) and that is what the trip computer says.
By the way the mpg for the run has improved by about 2mpg since the arrival of the Wortecs and the remap as Paul predicted.
V10JRR
By the way the mpg for the run has improved by about 2mpg since the arrival of the Wortecs and the remap as Paul predicted.
V10JRR
demolition man said:
I still can't get over how much the cruise control helps.
With the electronic throttle being monitored many times a second, it does a much better job of feathering than my fat plates of meat
With the electronic throttle being monitored many times a second, it does a much better job of feathering than my fat plates of meat
I remember once on Top Gear that Jeremy was in an Audi 8 diesel and noticed that cruise control used more?! Go figure.
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