Mel E Posted September 2, 2006 Share Posted September 2, 2006 I know many motorhomers try to monitor their fuel consumption, and I mentioned a few weeks ago a method of monitoring the average using a technique called 'exponential smoothing' - no, don't yawn yet. I've been asked for details, so here goes! It is really easy to use in a simple spreadsheet, works brilliantly, and gives a really good running average, weighted as much as you want to the most recent fill-ups that is much better than most other methods such as: - average since new (doesn't show the CURRENT trend) - average of last 5 or 10 fill-ups (still to weighted to history). The formula is simple. Each time you fill up, you must fill to the top, note the mileage and cost per litre (to work out litres) on the fuel receipt, then calculate either litres/100 Km or mpg since last fill up - call this IMPG or Instant MPG. (Conversion factors for miles>Kms and Litres>gallons given later). Then: NEW AVERAGE MPG = AVERAGE MPG before this fillup * 0.8 + IMPG * 0.2 The 0.8 and 0.2 are the weightings. They must add up to 1.0 but otherwise you can use any values you like - .7 and .3 give more weight to current performance and less to history. If you're good with spreadsheets, use a defined variable instead of 0.8 (call it 'alpha') and then use 1-alpha instead of 0.2 and you can set alpha to any value you like. A typical spreadsheet might have the following columns: A - Date of fill-up (You input this on each row) B - Cost of fill up (You input this on each row) C - Cost per litre (You input this on each row) D - Cumulative vehicle mileage (You input this on each row) E - Litres of fill-up (=B/C) F - Kms run (=(D this row - D previous row)*1.60935 (converts miles to Kms_ G - Instant Litres per 100 Kms (= E*100/F) H - Instant MPG (=282.3738/G) I - Average Litres per 100 Kms (= (I previous row*alpha) + G*(1-alpha) J - Average mpg (= (J previous row*alpha) + H*(1-alpha) To start the averages running, you need an initial 'previous row' before the first fill up - simply enter the average for the first fill-up and off you go. If you're really good with spreadsheets, include a graph of instant and average mpg. I've included the Litres / 100 Kms measure because I find it helps me get used to this metric measure, but leave it out if you're an anti-metric protester! (As I've said before, Nelson at the Nile and Trafalgar ensured the world speaks English rather than French, so I'm quite happy to let them measure things as a consolation prize!). Happy monitoring! Link to comment Share on other sites More sharing options...
Clive Posted September 2, 2006 Share Posted September 2, 2006 Autotrail Scout on 312 Merc 26.6mpg (towing a twin motorcycle trailer) average over 2019 miles in France. Link to comment Share on other sites More sharing options...
david lloyd Posted September 2, 2006 Share Posted September 2, 2006 2006 Knaus Sun Ti 650 MF on 2.5 dci Renault Master at maximumload of 3500kgs = 28.09 mpg after 2950 miles from new. David Link to comment Share on other sites More sharing options...
Brian Kirby Posted September 2, 2006 Share Posted September 2, 2006 2005 Burstner T585 on 2.8 jtd Fiat Ducato "Power", 146 hp, 3,250Kg laden.16,588 km travelled from new: 24.56 mpg. Link to comment Share on other sites More sharing options...
Geoff Bell Posted September 2, 2006 Share Posted September 2, 2006 FORD FREETEC 698G 3850KG 2.4 TDE Fully loaded but not weighed 1400 miles round trip in france 80% motorway 23.1 MPG Link to comment Share on other sites More sharing options...
Dave Newell Posted September 2, 2006 Share Posted September 2, 2006 1990 Autohomes Highwayman on 2 litre petrol Talbot Express chassis. Current average over 3.5 years = 22.34 MPG. Continuous checking carried out as almost any mechanical problems show them selves in the fuel consumption first. D. Link to comment Share on other sites More sharing options...
Don Madge Posted September 3, 2006 Share Posted September 3, 2006 Timberland Freedom Fiat Ducato LWB High top 2.8 JTD. Three years old with 42,000 miles on the clock. I don't usually bother to check the fuel consumption closely but when we decided to have The Van Aaken Smart Box http://tinyurl.com/dvala fitted We did a before and after check. After having the smart Box fitted to my Timberland in April 2005 I decided to do a fuel consumption check on a 4200 mile trip around the Iberian Peninsula. We normally cruise at about 90/100 KPH (usually the van is fully loaded 3300kgs) and with the cruise control set we found that we did not have to change down for the hills which we would have expected to have change down on before the box was fitted. I tried to keep an accurate check when refueling, It's difficult at times when you are trying to fill the tank right to the brim. The 4200 miles on the continent returned the following:- Overall 33.08 MPG Best 36.25 MPG Worse 27.73 MPG On a previous trip to France (1400 mile) before the Smart box was fitted our overall MPG was 30.34. I must point out the smartbox was fitted for convenience rather than fuel economy. Don Link to comment Share on other sites More sharing options...
Mel E Posted September 4, 2006 Author Share Posted September 4, 2006 Don, I can't fit an ECU modifier yet as it's not out of warranty - the Renault comes with a 3-year pan European warranty and recovery/roadside service. Modifying the ECU invalidates that and I reckon it's worth a lot more to me than the odd couple of mpg. Link to comment Share on other sites More sharing options...
Don Madge Posted September 4, 2006 Share Posted September 4, 2006 [QUOTE]Mel E - 2006-09-04 6:16 PM Don, I can't fit an ECU modifier yet as it's not out of warranty - the Renault comes with a 3-year pan European warranty and recovery/roadside service. Modifying the ECU invalidates that and I reckon it's worth a lot more to me than the odd couple of mpg.[/QUOTE] Mel, Mine is the same that's why I waited and had it fitted in the last eleven months. I did not do if for the fuel economy but for the ease of driving, any way the last years warranty on the Fiat is not worth the paper it's printed on. I remove the unit when it goes in for servicing anyway. Don Link to comment Share on other sites More sharing options...
Mel E Posted September 4, 2006 Author Share Posted September 4, 2006 Don, Unfortunately, they can now tell if you've fitted a unit. After all the ECU is a computer and it stores all relevant info about the engine. Link to comment Share on other sites More sharing options...
Don Madge Posted September 4, 2006 Share Posted September 4, 2006 [QUOTE]Mel E - 2006-09-04 8:55 PM Don, Unfortunately, they can now tell if you've fitted a unit. After all the ECU is a computer and it stores all relevant info about the engine.[/QUOTE] Mel, I'm out of warranty now so it's not a problem :-D Don Link to comment Share on other sites More sharing options...
Mel E Posted September 12, 2006 Author Share Posted September 12, 2006 Don, Enjoy Istanbul and I hope the predicted earthquake doen't hit yet! Link to comment Share on other sites More sharing options...
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