How accurate is onboard computer?

pappajohn

LIFE MEMBER
Aug 26, 2007
40,365
38,122
Dark side of the moon
Funster No
172
Exp
Since 2005
Check it and see.

Fill tank
Zero MPG
Drive til nearly empty
Refill to top
Note litres needed to fill and current mileage. (Divide litres by 4.54 to get gallons)
Calculate MPG
Check against computer.

Personally I find the MPG computers a waste of time....when you need fuel, you need fuel.
 
Last edited:
Oct 30, 2016
878
1,436
Colchester
Funster No
45,854
MH
Le voyageur 8.5
Exp
On 3rd van so not a total newbie....
Overall I think the fiat one is reasonably accurate, the issue I have is filling consistently, as it suddenly fills and will spurt back, as a result, I only now fill to the first cut out, which depending on pump flow could be a couple of litres more or less than I have used.

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GWAYGWAY

Free Member
Sep 6, 2014
4,218
3,296
Dover
Funster No
33,216
MH
Hymer ML I 580
Exp
4 years
I do not know if it is accurate but mine says between 14.1 to 14.4 km per litre from start on a new trip per day, usually at a steady 55-60mph.

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Oct 30, 2016
878
1,436
Colchester
Funster No
45,854
MH
Le voyageur 8.5
Exp
On 3rd van so not a total newbie....
I do not know if it is accurate but mine says between 14.1 to 14.4 km per litre from start on a new trip per day, usually at a steady 55-60mph.
That's about 40mpg! Is that downhill all the way?!
 

Lenny HB

LIFE MEMBER
Oct 18, 2007
32,442
61,707
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
All three Ducato's we have had have been accurate between 0.2-0.5 mpg compared to tank brimming method over several tank fulls. Always tend to read slightly under.
 
Feb 9, 2008
3,726
4,844
SW Scotland
Funster No
1,453
MH
LP Coachbuilt
Exp
Since 2008 after caravanning for 20 years
Mine reads slightly under, it will show 28 - 29 m.p.g when I am actually getting 30 - 31 m.p.g. on tankful to tankful. I record all my fuel purchases.
 
Jul 3, 2008
1,085
903
Lincolnshire
Funster No
3,154
MH
Autotrail Apache 700
Exp
since 1998
I never worry about fuel consumption, I look at it as,if I have to worry about a mile or two more or less from Fiats figures, then I cannot afford to run the van in the first place.:cycle:
 
May 7, 2016
4,303
5,895
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
I do not know if it is accurate but mine says between 14.1 to 14.4 km per litre from start on a new trip per day, usually at a steady 55-60mph.

That's about 40mpg! Is that downhill all the way?!

Possibly litres per 100km, which is how my Merc based Hymer measures it, and that is nearer to 20 mpg than 40.

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Oct 30, 2010
4,270
20,446
Suffolk or France or ........
Funster No
14,290
MH
A Class Carthago Chic
Exp
Since 2008
I use a fuel app on my phone to log fills and the onboard Fiat computer seems to mirror my results. Cant tell exactly as I zero the trip so frequently.

Richard.
 
Oct 27, 2017
1,003
1,876
Perth
Funster No
51,142
MH
Hymer A Class
Exp
Since 2014
Last October our 130hp Ducato-based Hymer showed 26 mpg for 2000 miles around Italy and Croatia. On the way home it suddenly went to 5.6 mpg. This was on both "A" and "B" journey logs. I have no idea why. I've subsequently replaced the starter battery, so the computer has reset. Any ideas?
 
Aug 14, 2013
527
465
Département 87
Funster No
27,512
MH
Profile
Exp
Since about year 2000
Your calculations are only as accurate as your speedo / odometer. In theory, therefore, you may be getting a figure which is up to 10% to your apparent advantage.

J
 
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