Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[dbdb]

Here are the results of my mpg test. Anyone can repeat it and compare.

Car: 2001 facelift 2.6V6 Elite saloon 70K miles.  Tyres: standard (17") at 30PSI. No passengers, tank a notch under full, not much weight in boot (7kg hydraulic jack and litre oil).

Route: empty reasonably flat motorway 5 miles each way with mpg averaged out to allow for wind and slope. No rain, little wind. Outside temp 5C

Mpg 36.8 with air con off ('eco'), 35.0mpg with air con on. 

My immediate conclusion is air con adds about 5% to your fuel consumption (at 60mph), about what I'd expect. I imagine at lower speeds it adds more, perhaps 10%.

Still seem a bit thirsty to me compared to my old 2.5 V6. I recall getting 50mpg at 55mph. I did have non standard 225/45 16s on it though so speedo was out.

[dbdb]

forgot to mention -  transmission: manual, GPS speed: 58mph, fuel: super unleaded 98. Last time I checked 98 gave 10% more mpg than 95.

[jonny2112]

Mmm. Interesting, thanks for this. 
I have the auto version and would be keen to test it in this way at some point when running properly again. I felt it was a little thirsty and hope that new cam gaskets and stat may improve efficiency slightly. I haven't tried 98 either, so worth considering on occasion.
I don't recall ever getting 50mpg out of my 2.5, but tbh I never did any such controlled tests. I did find it easier on fuel, but it was manual, and petrol was cheaper. Not a lot, mind you ......

[ajsphead]

Might be able to contribute something interesting to this as I've been doing a series of consumption tests as bits have broken and been replaced.

2.5V6 manual estate. 2 passengers no load 137K. This might reveal more to those of you who know more than me but here goes.
The range is tested from a good representation of the proportions for combined cycle at the lower end to long distances at about 75mph for the upper end. Tyres all inflated to figures off the forum. Engine serviced including air filter at 134K. 600 miles or so in each of the stages.

Standard factory trim. 27.2-29.7mpg and a pig to stop stalling with a gentle take off (normal for me).
Long intake pipe removed from behind o/s/f headlamp. No longer a stall fest.
Throttle bodies cleaned and K&N panel filter fitted and the averages don't change enough to notice but the throttle response is a frac better possibly.

Diesel diff fitted 28.5-31.6mpg.
M tech chip fitted 30.4-33.8mpg and throttle response and acceleratiion is back to standard spec/diff levels. It's also developed a really nice V6 rasp if you give it some beans.

All the figures are from the same pump at the same station brim to brim (literally).

As a comparison my 3.0V6 4WD auto x type Jag in factory spec does 26.1-31.7 under identical conditions.

Make of that what you will.

[dbdb]

Good point on the air filter, I didn't mention I replace mine 500 miles ago.  I keep meaning to check and change the plugs. The pedal test shows no error codes.

The official Govt test is here (now has diagram showing the different speeds) http://www.dft.gov.uk/vca/fcb/the-fuel-consumption-testing-scheme.asp

As you can see it is too complicated toreplicate it, I think setting cruise on a level run is the only way to get a repeatable test.  I'll see if I can get hold of my old 2.5 figures, I do recall almost getting the MID to 50mpg on a long slow motorway run but I would need to adjust for the smaller tyres used.

[Webby the Bear]

Please forgive my ignorance but how are you calculating the MPG? by the trip computer or brim to brim? Apologies if ive missed how you've done it

[TheBoy]

Undoubtedly, the 2.5 and 3.0 are more economical than their later counterparts, 2.6 and 3.2, with no noticible difference in performance.

[dbdb]

Please forgive my ignorance but how are you calculating the MPG? by the trip computer or brim to brim? Apologies if ive missed how you've done it

Using the trip computers average MPG  on the MID, set cruise control and avoid any trucks or cars that may force you to switch off cruise, then reset the MID average consumption  by holding down the stalk button until stars appear, after the dashes appear  (anyone know what the difference is, I assume the stars erases ALL history and the dashes don't?).  My trip computer is spot on, as regards range anyway. At the end read off the average mpg and switch off cruise.  Reproduce the test in the opposite direction to even out slope and wind.

I don't think brim-to-brim is accurate enough for such a short test but by all means use it over a tank full to check your trip computers consumption figures. If they are Ok it must be safe to rely on the average consumption (assuming the mileage is correct).

[Aundie]

I just put petrol in mine when it needs it. wouldn't drive a car like this if I was worried about fuel consumption trip comp says average consumpion is 19.9 mpg. 2.5 auto 99'

[Webby the Bear]

It's definitely my own fault that I don't really understand the trip computer but here goes...

I got ''Inst. Con'' and if you were to keep watching it it changes every split second with various MPG values so how am I to use this correctly where by I'm given my average MPG over a journey or a particular distance.

I have also the usage which just stays at 20MPG and doesn't alter 

[biggriffin]

I just put petrol in mine when it needs it. wouldn't drive a car like this if I was worried about fuel consumption trip comp says average consumpion is 19.9 mpg. 2.5 auto 99'

  as above. i've got a 3.2 estate doing 22.mpg according to the trip. that changes to 30mpg on the motorway,...
     jf id have wanted to save fuel id have bought a micra and hug trees O and read the guardian.

[dbdb]

It's definitely my own fault that I don't really understand the trip computer but here goes...

I got ''Inst. Con'' and if you were to keep watching it it changes every split second with various MPG values so how am I to use this correctly where by I'm given my average MPG over a journey or a particular distance.

I have also the usage which just stays at 20MPG and doesn't alter 

When on average (usage) MPG you need to hold one of the stalk buttons for a few seconds.  Forget which one it is but it isn't the one that moves you on and there are only 2.  This resets the average which in your case will have started a long time ago and it then begins showing a new average from the time you reset it. Inst Con is pretty useless.