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.