There are few factor to heavy fuel consumption
- tyre pressure
- dirty air filter
- high viscosity engine oil
- badly carbonized spark plug
- cold air intake is from the inside engine bay
- vehicle is too heavy as compare to the engine horsepower
- clogged cat converter
- dirty throttle body
- poor clutch
- using over sized tyre
- worn out tyre thread
- tyre alignment not correct and excessive toe angle
- aircond setting is too low example set at 18 celsius
- heavy foot on the throttle
- poor injection quality by the fuel injector
- placing luggage box above the roof rack
So, if you manage to rectify above mentioned, you are gaining back your losses . However you have to give some allowances such as aged of the vehicle and mileage. Such high mileage vehicle will effect the fuel consumption, perhaps its time to conduct a major overhaul or a top overhaul.
Hope my short advice help's you.
