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Old 23-09-2019, 05:54 PM   #1
bidderman1969
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trying to work out diesel MPG

bear with me on this.....

been getting fuel in the oil, so i had to try something as someone had said it could well be something to do with it trying to regen more times than normal, but i have never had any DPF issues yet, so thought i'd try something out

i did an airport run sunday, reset "average fuel consumption" drove normally to airport, 42.5 mpg, trip starts off rural, fairly hilly, for around 10 miles, and about 40 mile in total would be the "run", fairly consistent 70 mph slowly for some traffic, but only to 5th at one point, M25 stayed in top gear, varied between 50 and 75 mph.

on the way back, i thought i'd try the "keep revs up, lower gear" technique to see if i could thoroughly clean the DPF system out, or see if it might help, so from heathrow to home i avoided 5th and 6th gears very weird experience having the car roaring away at around 3000 revs all the way home, mostly 65-70 mph and had to discipline myself not to change up regardless. back to the area i started of at, 45.5mpg



how do you work that one out?????

car does seem to be smoother a little, might try this routing a few more times
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Old 23-09-2019, 06:28 PM   #2
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Plenty of factors but you were probably nearer the power band and had less effort from the car to maintain your speed. Engine under less stress/load (i.e when you grumble along at low RPM and then put your foot down, and feel the vibrations putting the engine under load, it dumps fuel in to try and pick up your RPM). By staying closer or in the main power band, you avoid that.

Going up hills some people seem to think leaving a car in a certain gear and slowing down some what is themost efficient when often it's not .

Too many factors to take into account. Driving style, gear changing etc etc
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Old 23-09-2019, 06:29 PM   #3
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Quote:
Originally Posted by Starbuck88 View Post
Plenty of factors but you were probably nearer the power band and had less effort from the car to maintain your speed. Engine under less stress/load (i.e when you grumble along at low RPM and then put your foot down, and feel the vibrations putting the engine under load, it dumps fuel in to try and pick up your RPM). By staying closer or in the main power band, you avoid that.

Going up hills some people seem to think leaving a car in a certain gear and slowing down some what is themost efficient when often it's not .

Too many factors to take into account. Driving style, gear changing etc etc
Does seem really weird tbh
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Old 23-09-2019, 06:48 PM   #4
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Quote:
Originally Posted by bidderman1969 View Post
bear with me on this.....



been getting fuel in the oil, so i had to try something as someone had said it could well be something to do with it trying to regen more times than normal, but i have never had any DPF issues yet, so thought i'd try something out



i did an airport run sunday, reset "average fuel consumption" drove normally to airport, 42.5 mpg, trip starts off rural, fairly hilly, for around 10 miles, and about 40 mile in total would be the "run", fairly consistent 70 mph slowly for some traffic, but only to 5th at one point, M25 stayed in top gear, varied between 50 and 75 mph.



on the way back, i thought i'd try the "keep revs up, lower gear" technique to see if i could thoroughly clean the DPF system out, or see if it might help, so from heathrow to home i avoided 5th and 6th gears very weird experience having the car roaring away at around 3000 revs all the way home, mostly 65-70 mph and had to discipline myself not to change up regardless. back to the area i started of at, 45.5mpg







how do you work that one out?????



car does seem to be smoother a little, might try this routing a few more times
What car is it?

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Old 23-09-2019, 07:48 PM   #5
bidderman1969
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Quote:
Originally Posted by Lexus-is250 View Post
What car is it?

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Kia Optima 1.7 CRDi, manual
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Old 24-09-2019, 01:16 PM   #6
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If you want to regen more use ****e fuel. If you dont, use shell vpower but be warned after 300 miles mine gets hissy because it hasnt regened enough so I cant use vpower. I also get poor mpg on vpower, something to do with the fact its liquid gas not diesel and so the calrific value is lower. If youre a taxi, use vpower, if motorway use anything. Some say theirs regens all the time on premium fuel and hence its cleaner, others say regens less as it doesnt need to.

Really its down to the engine and drving style.

My volvo 5 cylinder hates vpower, likes churning through normal fuel, but as its a diesel it needs an italian tune up especially as autos love to keep the revs low. It hates texaco fuel. No idea why.

Your scenario, too many variables, cold engine, vs warm engine, coked vs decoked, regen vs no gen, fuel quality, moiture in tank, gradient and load under certain revs, etc. etc.

The only way you could test is fill tank to the brim and work out your mpg manually on 3 tanks of one type of fuel, your computer cant be trusted, your maf senor may not have coped with the italian tuneup airflow, and so, calculated all wrong.

Im currently going through a test, three tanks of a brand and type of fuel ,recording 120 litres to miles of 3 weeks average driving. Gonna take me a while but ill have a best fuel type, best brand and best additive combo in the end!

3 tanks of each and record the milage, cost and then finally mpg and cost per mile:

BP
BP ultimate
Shell vpower
Shell fuelsave
Tesco
Asda
Morrisons
Sainsburys
Esso
Esso premium
Jet
Jet premium
Texaco
Texaco premium
Best non-premium plus Millers Ecomax each fill

My tanks 80 litres so thats about 650-700 miles.... x3 x above 14 = almost 30k! so that's almost 2 years driving to find out, variables of summer and winter.. maybe ill do this over seasons too, to 4 years or maybe im thinking it too much!! TO be honest ill probably just stick to shll/bp/jet/texaco/tesco as theyre the closest stations, the rest can jump as i will neve ruse them regulalrly.

Last edited by NorthantsPete; 24-09-2019 at 01:40 PM.
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Old 24-09-2019, 02:33 PM   #7
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I use Esso about 85-90% of the time
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Old 24-09-2019, 06:15 PM   #8
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Another thing to add, The biggest discrepancy with your MPG is that you calculated them on what is essentially 2 routes, there could be an unnoticeable incline on the outward journey which means a descent/decline on the return.

For example, I do a regular jaunt 150 miles away. On the way there, my 2.0HDi uses about £17 worth of Diesel, on the way back about £23.

A good average would be the SAME journey i.e. going the 1 way multiple times with your different driving styles to see if any difference.
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Old 24-09-2019, 06:31 PM   #9
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Yeah can see what you’re saying, personally I reckon it’s fairly equal, if anything, way back would have been more uphill, but yes, will try several trips and assess again,
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Old 24-09-2019, 06:57 PM   #10
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Increase in MPG could also be due to the fact you had less weight in the car on the return journey?
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