V70: Engine Plummeting fuel consumption

[apersson850]

Originally Posted by uknowiama

I thought this was standard practise? With whatever car you have. Fill up tank. Reset trips. Reset average mpg. Always do this to keep an eye on things. How many miles gone before used 1/4 tank then 1/2 tank. How to keep an eye on health of engine - when factored in with type of driving being done - long runs, short slow town trips?

Absolutely not. The trip meter is used to measure how long a trip is, not how long the fuel lasts. The average fuel consumption indicator is used for that, to indicate the average consumption over some stretch of driving, since last reset. You may select to reset at the beginning of the year, at the beginning of a vacation trip or at whatever other occasion you feel like. But not a routine reset at each refill.

If you want to keep an eye on your engine, look at the actual consumption now and then. If you have that displayed you'll quickly learn what to expect in different driving conditions.

Now assuming everything works as it should, the average is calculated from the last reset. If you have driven for a long time, it doesn't change noticeably even if you start towing a caravan.
The estimated range is based on a moving average, collected during the last 30 km of driving. Thus if you start towing a caravan, it will take 30 km of driving before the full impact of the increased consumption can be seen on the estimated range. And the opposite, of course.
Resetting the average doesn't affect the estimated range at all.

Your average fuel consumption doesn't drop when you two a caravan. It increases. It's just the custom of displaying range, not consumption, that makes the number drop. If you do display consumption, you would see that it increases from, say, 7 to 12 l/100 km.

If you want more detailed observations of the consumption, don't forget the histogram in the center display, under MY CAR/Trip statistics.

[yostumpy]

Originally Posted by apersson850

Absolutely not. The trip meter is used to measure how long a trip is, not how long the fuel lasts. The average fuel consumption indicator is used for that, to indicate the average consumption over some stretch of driving, since last reset. You may select to reset at the beginning of the year, at the beginning of a vacation trip or at whatever other occasion you feel like. But not a routine reset at each refill.

Can't agree with this, sorry. By resetting each time at fill up, I calculate actual mpg with fuel purchased, an the avg readout is always 1-1.5mpg higher. By resetting each time, those with a mind to 'hypermile' can see from the beginning of each tank , how they are doing. As I've said before , I find it fun, and I'm not 'driving Miss Daisy' as some would say. If you only reset once a year, then you get a bit lost and disillusioned, as it never seems to change much, but when it's reset per tank, and it's a bit low because of urban traffic, when a longer day trip comes along, gains can clearly be seen by using hypermiling methods, and i is VERY satisfying. By doing this I could clearly see that the 400 odd miles between Dijon and Cassis netted me an actual 51.67 mpg, whreas with a 'running total'I would not necessarily had the mind to eek that last bit out of it, and it may only have been 46mpg ish. Maybe I'm just sad.

[Cloth Ears]

Originally Posted by yostumpy

Can't agree with this, sorry. By resetting each time at fill up, I calculate actual mpg with fuel purchased, an the avg readout is always 1-1.5mpg higher. By resetting each time, those with a mind to 'hypermile' can see from the beginning of each tank , how they are doing. As I've said before , I find it fun, and I'm not 'driving Miss Daisy' as some would say. If you only reset once a year, then you get a bit lost and disillusioned, as it never seems to change much, but when it's reset per tank, and it's a bit low because of urban traffic, when a longer day trip comes along, gains can clearly be seen by using hypermiling methods, and i is VERY satisfying. By doing this I could clearly see that the 400 odd miles between Dijon and Cassis netted me an actual 51.67 mpg, whreas with a 'running total'I would not necessarily had the mind to eek that last bit out of it, and it may only have been 46mpg ish. Maybe I'm just sad.

I agree with this (not the bit where you are just sad!) and I always reset the trip when I fill up. I usually brim the tank, so I have a fair idea how many miles until empty again too. My V60 has 2 trips, so I reset one for the tank, and can leave the other for different things, like the mileage on our upcoming holiday or whatever. I think having 2 trips is very useful.

[apersson850]

You can just as well make a note of when you fill and how much, and calculate the average the old way. From the post, it seems you do that too, in addition to letting the car do the same thing.
This is what we did back in the 1980's, but things have changed since then.

Today, we have more options.

The trip statistics histogram is better for checking individual trips, if you want to see if you can beat your best effort for a certain journey, or something.

The momentary consumption is better for checking if something suddenly broke, like when the lambdasond broke on my 854 Turbo once. Suddenly the current consumption went from around 8 l/100 km to 20. Obvious that something was wrong.

The resettable average is good for checking a holiday trip or other special occasion, since you can reset it as you like.

If you for some reason want to check a particular range of days, after the fact, you can use the trip log in Volvo on Call and calculate the average of any driving done the last three months.

[yostumpy]

''This is what we did back in the 1980's, but things have changed since then''

Yes we did, and it is still the most accurate method, ''technology ain't what it used to be''.
Anyway , only recently, do I have a car with a radio, and it runs on squashed dinosaurs.

[uknowiama]

Who would of thought a simple comment of what I thought most people did when filling up would cause further debate…

Just got back from France since first brimming tank in UK before departing. And filling up a further 3 times. I did not reset the trips T1 nor T2. Nor reset the average mpg calculator.

99% Motorway / Autoroute. 130 kmh in France where allowed. Journey out and in - each taking approx 16 hours door (South Wales) to door (Aix-en-provence) = avg 40.8. I learnt the trips only go as high as 999 then start again

Take point about instant mpg to see any issues - i.e car don’t feel right - not as torquey - type situation - see excessive mpg to back up thoughts.

Will also use miles per tank achieved and type of driving done (I'm the only driver) as an idea to current health of car / engine.

I will probably continue to reset trips and mpg with each tank - am creature of habit.

Am aware mpg from computer isn't as accurate as manual calcs brim tank to brim tank. So holiday mpg is prob 39 mpg? Given engine sat at 2300 rpm for hours at a time. I thinks shows healthy.

[Tony Rama]

Did the OP find the cause of his high fuel consumption, or did I miss something?

[apersson850]

Originally Posted by uknowiama

I learnt the trips only go as high as 999 then start again

Yes, in the dashboards with the old style clocks it does. Rolls over after 1000 km here, so probably 1000 miles for you.
The TFT display style dashboards have another digit.

Back then, my 854 Turbo 1994 had a more clever trip computer. The standard trip indicator was still with mechanical rollers back then, with km with one decimal. But the secondary trip indicator, in the trip computer, had variable resolution. Every 10 meters up to one km, then with 0.1 km resolution until you reached 1000 km, then integer km resolution.

Not so clever in the XC70 from 2012.