This issue becomes topical directly in the autumn months. Every year, exactly in autumn, I get quite many e-mails with a description of an identical situation:
“I put the engine of my car in order, Stratified charge should be restored, but – the fuel consumption has not reduced!”
Why directly in autumn the described situation appears – a moment later.
Initially: make sure, that the engine really uses a Stratified charge. More about it read here (E series) and here (F series).
If the engine still is not using a Stratified charge, typical reasons are mentioned here (E series) and here (F series).
If the engine really uses a Stratified charge, at that moment the fuel consumption is reduced for 15 .. 25% (comparing to Homogeneous mode)! There is no deviation from this statement – that is indeed it!
At this moment we get till the essence of the entry – why the Stratified charge doesn’t “help” in autumn?
Every year, in autumn, (in Europe – directly here 99% of vehicles with engines of N43/N53 engine family are in use):
a) the outside temperature is lowering. For example, in this year, in the first half of November, the average temperature of the daytime in Baltics dropped for at least 10 .. 15oC, comparing to October. The lower the temperature of the environment the longer time the engine takes to warm up. While warming up, it uses more fuel – every experienced driver knows that;
b) slightly, but still the fuel consumption is increased by using additional heating for windows, seats, mirrors, steering wheel, interior heating (to run the vent motor); quite often in cold weather the car is left to “warm-up” for several minutes – during this period, the fuel is wasted (the car is not moving);
c) the number of precipitation increases significantly. When driving on the wet road (with speed around 90 .. 100km/h), the fuel consumption increases for at least 1 liter on 100km. If it’s raining and the tires have to “fight” the layer of water on the road, the fuel consumption increases even for 2 liters on 100km or even more during heavy rain. If the snow falls, fuel consumption increases even more dramatically!
d) in autumn, many drivers change the tires form summer set to the winter set. Winter tires have a softer material, the tire pressure tends to be lower, they can be equipped with studs. All these obstacles increase rolling friction and fuel consumption;
e) the weather conditions are getting worse in the autumn. Naturally – the drivers are driving more carefully, the average driving speed is reduced. Lower average speed, longer “sitting” in the traffic jams – one more obstacle to increased fuel consumption;
f) and finally – when the winter comes, our driving habits change. In the warm weather we drive the longer distances, take longer trips, in autumn and winter – “first necessity” routes are dominating. If driving shorter distances via city – the fuel consumption increases for granted.
What is the summary of this entry?
Every year the fuel consumption of our car increases due to obstacles mentioned previously. It is inevitable. If the engine restores Stratified charge and the total fuel consumption has not increased – so the Stratified charge is performing its task perfectly, and actually the fuel consumption has even decreased! From this moment, your car consumes less fuel – but equal conditions have to be compared!
And finally: how to measure fuel consumption.
The fuel consumption CAN NOT be measured by the “dropping speed” of the fuel indicator. The fuel indicator is not exact, you will not be able to indicate the difference of several liters – the measurement error is too large.
The fuel consumption can be measured, using indications of the onboard computer, but: the indications of the onboard computer have to be cleared (typically – pressing the BC button for a longer time) before starting the measuring. Reason – previous data could be (and usually they are – if are not recently cleared/updated) from many thousands of km. If the BC data are not cleared, the changes in them you will see only after several thousands of km (and not immediately – as you would like).
More correct/exact is the “full tank” method. It means, fill the full tank, drive X km (not less than 200 .. 300km), repeatedly fill the full tank. Calculate the consumption, using mileage and the amount of fuel refilled.
Note: during first and second filling, use the same fuel station and the same refueling gun. Fill till the 3rd “click”.
To evaluate fuel consumption (changes in fuel consumption), use the same conditions in all tests. It is not correct to compare the fuel consumption between driving sessions outside the city (on highways, etc.) with spending time in traffic jams. Of course, in the second case, the fuel consumption will be higher! The Stratified charge will not help – conditions are too different!
