AOA
regarding increasing fuel efficiency in your toyota Aqua i would like to share my experience aswell
i been driving toyota aqua since 2015 till present.
and have kept two model 2013 and 2015 (currently driving)
with reference to all other members feedback regarding 0w20 oil and low resistance tires etc all stand correct and should be followed to ensured maximum efficiency
regarding your fuel efficiency of 19km on motorway. it is a good average... i get 19 to 20 on lahore motorway with the same speed bracket of 120 to 125 average
keeping and driving 2 different model aqua's i noticed and like to share my experience for better mileage .
keeping the heater at optimum level usually at 24 degrees. as the heater requires heat from the radiator hybrid engine tend to shut down when under 50 kms... example if your temperate is above 26+ the engine will keep turning on to maintain heat in the cabin even if you have more than half battery.
outside temperature also plays an important role.. in winters in islamabad even without a heater i get around 24 km avg... however during my visit to lahore in feb-2019 i was getting 27km after getting a tank refill of normal petrol from TOTAL pump and resetting the ODO trip mileage... thus locality temperature plays an important role.
getting more average from TOTAL Pumps petrol as compared from other pump such as PSO and Attock . honestly not tried shell yet.
after getting your tank refill i would suggest to reset the mileage to 0 and try to drive the first 150km on battery keeping speed under 50kms... its get irritating when driving slow but i experienced 23.5 to 24.5 avg in winters and 24 km plus in summers plus your tires and brakes wear out less at low speed.
most Importantly.. hydrid battery fan need to be cleaned after 50000km plus depending on the dust conditions... this fan is located under the left side back passenger seat... this is a sensitive matter on how to clean this fan because if any dust goes inside the battery, this will affect the battery life as it will get more hot and warm and reduce life. using a blower will never be a good option and never listen to your mechanic ustaadi on this matter..
i would suggest all hybrid owner to view videos on youtube how to clean this fan and update them selves and then go to the mechanic to get it cleaned and under your own supervision..
hope my experiences will be beneficial to other... best regards