When I first got my Patrol I got similar economy, I tried changing the fuel filter and using injector cleaner, changing the air filter and spark plugs, distributor cap and even adjusting the valve clearances. Economy got a bit better, but not really that much better. After about a year I noticed that the car took a long time to heat up but after 10-15 mins of driving the temp showed normal. I changed the thermostat and it heated up really quickly but also used dramatically less fuel. It turned out that the temp showed as normal but the coolant was actually still a bit cold so the car stayed in cold start mode and ran really rich. It might be worth looking at because 25 l/100km is definitely not normal.