Is the trip computer honest MPG wise?

[OdinEidolon]

Hi all!
I just bought a 2.2HDi saloon. I had the opportunity to take it on a highway trip, about 120 miles.
At a steady (cruise control) 75mph the trip computer is telling me I am averaging 60MPG.
I'd love it, but it sounds too good to be true, doesn't it?
The car has got around 110000 miles and is from 2001.

Does the trip computer usually exaggerate the MPG? I know some cars do... for example in my mum's Clio.
Also, is the average consumption estimated by the computer only through engine data (usual french makers crappy way) or is it directly measured using a flowmeter (other maker's way of doing this)?

PS: yep, I'll start writing down refills and miles (kilometers actually) next time I refill.

[highlander]

It's being honest, really - the trip computer is good, and the HDi is excellent for miles per gallon. It's a really economical engine.

I can get between 35 and 40 MPG from a 2.2 petrol engine (on motorway driving) and anywhere up to 67 MPG driving at 40 MPH in 5th gear in town, so I reckon you're spot on with the 60 MPG you're getting with your 2.2 HDi.

[Busman]

I did check my 2.0 HDI trip computer when I got the car as it was hard to believe how good it was on fuel. I did the traditional full tank to full tank and noted the gallons and miles and found the computer to be spot on.

[OdinEidolon]

Well, that's just plain amazing.
Someone told me that the 2.2 did use more fuel than the 2.0, but sincerely if it still manages 1400 damn kilometers on the highway with a tank... I'm impressed.

[rwb]

No, the values are rubbish.

Compared to brim-to-brim filling I see a difference of between 10 and 14 mpg.

At present my average since last fill is 42mpg, and I expect the next brim calculation to show about 55.


60mpg is the minimum you should be getting on a run
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V

[OdinEidolon]

No, the values are rubbish.

Compared to brim-to-brim filling I see a difference of between 10 and 14 mpg.

At present my average since last fill is 42mpg, and I expect the next brim calculation to show about 55.


60mpg is the minimum you should be getting on a run
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V

I don't get it. You say values are rubbish but that 60 MPG is the MINIMUM I should get? So in your opinion I should get BETTER values than this?

[rwb]

I guess the accuracy of the computer varies from car to car, so you don't know how accurate the computer is until you have compared it to brim-to-brim calculations.

I find that for me:
(what the computer says) + 12
tends to be the truth.

Come to think of it, at ~75mph I would expect my computer to be showing 45-50mpg, but you have 45hp more than me and a longer ratio in 5th.

[OdinEidolon]

I guess the accuracy of the computer varies from car to car, so you don't know how accurate the computer is until you have compared it to brim-to-brim calculations.

I find that for me:
(what the computer says) + 12
tends to be the truth.

Come to think of it, at ~75mph I would expect my computer to be showing 45-50mpg, but you have 45hp more than me and a longer ratio in 5th.

Yep. I'll do some calculations in the news few weeks and report back.

[Gary406]

there not 100% accurate i beleive but are not far off.

i do beleive your 2.2 hdi will acheive 60mpg on the motorway

[OdinEidolon]

there not 100% accurate i beleive but are not far off.

i do beleive your 2.2 hdi will acheive 60mpg on the motorway

Nice! Do you think the 2.2 is more frugal than the 2.0 on the motorway? Since they have different end ratios... Mine is about 52 km/h (~32mph) per 1000 rpm, dunno about 90 and 110 2.0s. I do not even know if they have the same ratios, i suppose not.

[rwb]

viewtopic.php?f=5&t=12442&p=110686

only 27.5 in my 90

[bytecode]

viewtopic.php?f=5&t=12442&p=110686

only 27.5 in my 90

rwb - What kind of driving are you doing to get 27.5MPG?

EDIT;
OH Hang on - do you mean 27.5 MPH in fifth at 1000rpm?

[OdinEidolon]

viewtopic.php?f=5&t=12442&p=110686

only 27.5 in my 90

rwb - What kind of driving are you doing to get 27.5MPG?

EDIT;
OH Hang on - do you mean 27.5 MPH in fifth at 1000rpm?

guess so.

[406Kris]

I have a 51 reg 1.8 petrol and it sticks 39.2 MPG, I replaced the spark plugs and got 43 MPG on the first run bur my driving style differs on a daily basis and the trip computer still says 39.2

[alan forbes]

My 90 gives 43.5 on computer but brim to brim is usually 47-49