5 minute idle MPG

[ca-uk]

Had to move the car out of the way this morning - there was some good music on the radio so ended up sitting there for 5 minutes - was a bit surprised when i looked at my mpg count to see it at 9.9mpg! Granted, i wasn't moving anywhere, but that'd sucked a lot of juice through in 5 minutes (i've never seen it drop that far in other cars when i pause for music)

Ambient temperature about 10deg - thermostat never moved off the bottom (though olly is changing this for me this week) - i guess the e320 cdi must enjoy it's juice!

 

[davidjpowell]

I suspect a lot to do with no work to get it warm, and the thermostat.

Having said that no car is at it's best in that situation.

 

[ca-uk]

i'm never sure whether its best to jump in, move it, turn it off, or whether it's best to run it for a bit..

 

[corned]

Hang on a minute - have I missed something?

If you are stood on the spot, your consumption is 0.0mpg. If your car consumed one litre or ten in that time, the mpg would still be the same!

The reading is giving you the benefit of a 40mpg or so head start, which starts to take the average down if you are doing less than that. The car was being generous!

But as I said, by rights, your consumption was actually zero mpg.

 

[NormanC]

Hang on a minute - have I missed something?

If you are stood on the spot, your consumption is 0.0mpg. If your car consumed one litre or ten in that time, the mpg would still be the same!

The reading is giving you the benefit of a 40mpg or so head start, which starts to take the average down if you are doing less than that. The car was being generous!

But as I said, by rights, your consumption was actually zero mpg.

Rethink - I got it wrong so effectively removing my post!!

 

[ca-uk]

Yeh, i know my real number would be zero mpg - all i mean is, that i was taking the rate of decrease as an indication of how quickly it was munching fuel - i was actually thinking of seeing how long it would take to get to zero

I spend a lot of time sat in cars not going anywhere, so more than anything was just surprised to see how quickly it was going down compared to other cars..

 

[corned]

I see what you mean!

I suppose it depends on the true rate of consumption, but also on what the starting figure is.

I have an E320CDI (straight 6) and when I start out on a journey the initial mpg figure on the cluster is 40.2mpg (I think). This value must be preset somewhere in the electronics, and I would imaging that the figure will probably vary from model to model. Clearly an E63 is never going to see a figure like 40.2 unless it's being carried!!

I was a little surprised when I got my 'E' that the fuel consumption has no instantaneous readout. All other cars I have had with fuel computers had an instant readout. It was interesting to see how well you could adjust your driving style to increase this figure! That said, when you hoofed it and you were looking at a number 3 (on its own), it was a bit .

 

[ca-uk]

I'll have to see where mine starts - it's a year older than yours but is an I6 also - i wonder if the 40.2 is common or if it's based on your long term average? I'm obsessed with my mpg display!!

 

[corned]

I have wondered the same thing, but I have never seen it change on the display.

Also, I have never verified the computed figure by doing a manual calculation based on brim to brim mileage readings. One day...

 

[jorjXmckie]

Have to say when the rains came down 3? years ago I was stuck in traffic for a couple of hours going almost nowhere, and from a good 1/3rd tankful when I set off I finally had to turn around and head back where I started or risk running dry; the fuel gauge was dropping almost visibly (W211 E320CDI Avantgarde)
I did have the aircon on, just to stop the windows steaming up :-(
And yeah, my current W211 E270 CDI starts at circa 40 mpg and quickly drops to about 20 mpg then begins to climb as I get underway; averaging 39.1 atm

 

[wemorgan]

i'm never sure whether its best to jump in, move it, turn it off, or whether it's best to run it for a bit..

My instinct says turn off the engine as soon as you have finished your journey, no matter how short a journey.

Engine wear happens all the time whether the engine is cold or hot. So after a short journey, even if you continued to run the engine until it was warm, whilst the rate of engine wear would reduce, it would still be wearing. Hope that makes sense.

 

[grober]

Idling while stationary obviously makes a measurable difference to MPG figures hence the Stop/Start technology introduced by so many manufacturers to lower their CO2 figures. So your 5 minute idle listening to music might equate to 5 sets of traffic lights on a journey for example. God knows what one of many contraflows beloved of the custodians of our highways might amount to but I suggest a useful measurement might be 1 CD, 2 CD's, 3 CD's worth of petrol.