eveall

Alright, so i just picked up the brand new (demo) from the delearship and am confused by the fuel consumption readings. Being in Canada, it's all listed as litres/100km.
The estimates are 11.6/8.1/10.0 (city/highway/combined).
My best "average" is 14.3 L/100 km, but it's usually closer to 20 L/100 km
When i look at the bar graph on the nav system for the last 15 minutes, there's spikes of 40 L/100 km.
Could it be an error? Would the dealership have put in the wrong fuel? Not checked the tire pressure. I don't really understand how it could be this far off.
And just for the record, i'm getting used to the larger vehicle, so by no means am i pushing it off the line with hard starts.
Any thoughts?

markrivers

Don't trust the fuel consumption displayed on your dash.
The way I determine my mpg ( miles per gallon) is to get a full tank and drive it up to the low fuel indicator turns On.
most of my commute is predictable, home hospital, grocery etc.

Do this 3-5 times and that's the most accurate way of getting your fuel/kilometer ratio.
It's also advisable to use the same brand and type of fuel all the time, at least while you're doing the experiment. So if you're using Chevron premium, stick to that. If you prefer unleaded (87) then stick with that

Evitzee

Best way to check fuel consumption is to fill it to the brim and drive it until you need to fill up again, check actual fuel put in vs. distance driven and compare it to what the 'Since refuelling' number says. Mine is within a percent or two, close enough for my purposes. On my vehicle the odometer reads 3% slow so that will screw up whatever number you get. It's all an approximation, for one thing you don't know if there is an inaccuracy in the fuel stations pump (it happens).

In my experience it makes absolutely no difference what brand or grade of fuel you use. I'm many days into a road trip through the US and Canada and over the 5,600 miles since I left I've gone from sea level to 6,000 ft, from 105deg heat to 32 deg cold, and I even switched to regular grade after seeing the silly prices Canada charges and the avg per tank (physically calculated from fuel burned vs miles driven) has seen the average vary only from 24.0 to 23.5 mpg (uncorrected for odometer error). Never used the same gas station twice ..... it just doesn't matter. With no difference between premium and regular I'm just going to use regular from now on......I can not tell any difference in the driving feel or pickup. Why waste money?

markrivers

^ i agree with the no difference whether it's premium (91) or the regular unleaded (87)
as a matter of fact the 2012 RX 350 recommended fuel is THE Unleaded (87).
although some might argue that's why the 2012 is only getting 270hp vs the 2011 with a 275hp.

eveall

So i'm including a picture of the last 30 minute screen on the navigation system. I'm trying to figure out whether large aberrations are normal.
Once again, the fuel consumption is supposed to be 11.6/8.1/10.0 L/100km and you can see by the picture it peaks at 40 L/100 km (for my american friends, the 40 L/100km is equivalent to 5.9 MPG). Just curious if other people's displays are the same.

DunWkg

Okay let's convert this to something I might understand

Your stated estimates of liter per 100 kilometers and equivalent miles per gallon

11.6 L/100km = 20.27 mpg
8.1 L/100km = 29.03 mpg
10 L/100km = 23.52 mpg

Looking at your 30 minute chart, you expended about 593 liters or an average of 19.76 liters per 100 kilometer or 11.9 miles per gallon

So in summary you need to get the lead out of your foot. Of course there maybe other difficulties to consider.

On your chart, shorter lines are better, less fuel per 100km. As I understand it you're trying to reach your stated estimate of 10L/100km and you seem to be at 19.76 or about double the liters per 100 kilometers or about one half the mileage your striving for (11.9 mpg when you're striving for 23.52 mpg)

As to whether your chart is working, compare it to what you are doing during that minute of driving. A higher bar might indicate climbing a hill.


Anyone else??

eveall

OK, so first of all, there's not much lead in my foot in my opinion
Secondly, there's still a full tank of gas (maybe 3/4s). We haven't refuelled yet. So the 593 litres of fuel wouldn't even make sense.
Even if i was driving with a lead foot, i find it hard to believe i would be expending twice (sometimes even four) times as much fuel as the estimates.
I'm thinking there has to be some kind of sensor error. The salesperson told me to refuel, that would reset things. I'll try that, but i'm still curious if others with the nav system have this same kind of display.

eveall

Just took the car out for another spin. I was looking at the in-dash display of your fuel usage. It tells me while idling that i'm using 30 L/100 km (or more, that's as high as the display goes)...that's equivalent to 7.8 MPG...while idling!

DunWkg

Isn't the other factor your speed during that 30 minutes?

Your rate of speed, rate of fuel usage and distance traveled, should work backwards to amount of fuel used. My chart shows nothing if the car isn't moving. Yours might as it is looking at a 100 km calculation?

Pretty confusing for me.

eveall

If i'm coasting, it shows nothing. But when idling, it should show nothing, or very close to nothing, but it doesn't. It shows an incredibly high reading. I see what you're saying though, if i'm not moving at all, it would require a lot of fuel to go 100km (actually an infinite amount).

Obviously it's very confusing for me as well.

Evitzee

Forget the 30 minute readings, they vary wildly since you are starting, stopping, accelerating, cruising so they are going to vary all over the place. Keep track of consumption on a per tank basis, otherwise there is just too much noise in the data for it to be meaningful. Your graph is fine, your sensor is fine, but the data is being sliced too thin for it to be meaningful, it's a pretty useless screen, imo. Change it over to the Past Record screen (lower left button) and keep track of it that way. Start a new reading by zeroing out the Average fuel consumption reading on the steering wheel. I'd do it no more than once a day otherwise you are getting into to short a duration. Long term averages matter, not instantaneous readings.

DunWkg

http://oee.nrcan.gc.ca/transportatio...ut.cfm?attr=16