This is a very interesting subject. One that has completely baffled me since my last full service. I have had my car since 2010. It is a Toyota Auris 2.0 D4-D 1AD-FTV. Ever since owning it 4 years ago, I have had dreadful MPG. Even with driving at 30mph in 4th Gear or 65-70mph on the motorway in 6th Gear - I could only ever achieve around 300 miles before I got the low fuel message on the dash board. To say this was frustrating is an understatement I'd rather not use bad language. In my mind I thought I had tried everything there was to try in order to try to improve the mileage or at least try to figure out where I was going wrong. HOWEVER back in July 2014 a *Miracle* happened. Even to this day I cannot for the life of me believe that this is happening but it has and I do not know why. What I can do is explain to the best of my knowledge what I did in the time leading up to my improved mileage - maybe the same 'tricks' can work for you and everyone on this Auris sub-forum. It began like this: Since acquiring the car in 2010, I had been using Castrol Edge Turbo Diesel 5W-30 Fully Synthetic Engine Oil. Then since May 2012 to around June 2014 I began using Mobil 1 ESP Formula 5W-30 which took a lot of strain off the engine, this was especially seen on cold starts and motorway driving. It was amazing, worked wonders but was ultimately for those willing to pay a premium. With the fuel economy issues still reeling - I had sort of given up on the idea of caring and nourishing the car as it wasn't really doing anything for me in terms of economy and I slowly went back onto using Castrol Edge Turbo Diesel 5W-30 Fully Synthetic Engine Oil - it didn't cost the earth and did just as good a job as Mobil 1. Now with the engine oil swap overs I saw a relatively small improvement from time to time, from getting approximately 300 miles per tank I saw an increase to about 320 miles per tank. An extra lubricant I have always added to any car I've owned is Extralube ZX1 Micro Oil Treatment - it works wonders by bonding to metal surfaces without changing the properties of the oil, it reduces friction and ultimately puts less wear on the engine. You can buy them in 100ml and 250ml bottles. I usually buy the 100ml bottles (5 x 100ml bottles to be precise) from my supplier as it worked out alot cheaper. For the Auris I would drain the old oil (using Forte Engine Oil Flush) and add the new engine oil before adding the ZX1 - the instructions say add 225ml to a 2000cc engine (it comes with a leaflet telling you how much to add as per engine size). I would add 3 bottles (300ml) it does not harm the engine, just means theres a lot more friction remover in there (the more the merrier I say). The remaining 200ml would be used in the Gearbox Oil (150ml) and also the Fuel Tank (50ml). The Gear shifts would be a lot smoother and precise and the fuel tank would be lubricated and as the treatment went through the fuel system it would reduce wear on the components. Upon viewing the results my full tank miles went from approximately 320 miles to 340 miles per tank (regardless of whether I was driving with the foot firmly down on the motorway or driving conservatively on the motorway or public roads. I still didn't think this was good enough and I'm sure neither would anyone else. Now - In July 2014 I had my annual full service (brake discs, pads, engine oil, oil filter, air filter, fuel filter, brake fluid, pollen filter and this time round I had my gear box oil changed too and also added Extralube ZX1 Micro Oil Treatment to the engine oil, gearbox oil and the fuel tank). Also take into consideration that I had purchased the optional Cruise Control for the Auris back in February 2012 for £28.99. I had not used it a lot since then - maybe once or twice on the motorway, I mean it was there on the steering wheel but it was forgotten... if you understand where I am coming from... Shortly after having the full service done, I thought I would use as much of the remaining fuel in the tank before I fill it up again and add ZX1 Treatment and Forte Diesel Treatment and also give the engine a steam jet wash as it had a lot of oil and grease in the bay. It was cleaned up like new. At around 20 miles according to the range on the dashboard the Low Fuel light came on. I had never taken it below around 18 miles I would just immediately fill the tank up. I drove around until I reached 6 miles, staying close to a petrol station - I didn't want to be left stranded far from home without any fuel or breakdown cover. At this point I headed for the Shell Petrol Station and filled up on Shell V-Power Diesel until the tank almost brimming giving me enough head-way to add the 50ml of ZX1 Treatment and 400ml of Forte Diesel Treatment. I always reset the odometer completely from the time spent driving to the average mpg, etc. Everything gets reset when I fill up. The next morning on the way to work I thought I would start using Cruise Control all the time on the motorway and on the local roads. Rather then keep the odometer on the total miles the car has done, I always keep it on the amount of miles it is doing since its been filled up. At around 300 miles I checked the range on the dashboard and it said 80 miles left. I was completely shocked and bewildered - how was this happening? Then at 350 miles it was showing 50 miles left. at the 400 mile mark it showed the low fuel warning. I was shocked as it went from 340 miles per tank to 400 miles over a two week period. I then filled up with diesel again - I wasn't being picky - I just went to my local Esso Petrol Station which is 15 seconds away from my house. I continued using cruise control anbd staying within local speed restrictions at all times. For instance at 30mph when cruise control can kick-in I would use 4th gear, the engine speed would be around 1200rpm. At 40mph I would be in 5th gear at 1400rpm At around 65/70mph I would be in 6th gear at around 1850/1900rpm. Again over the next two weeks I gained more miles per tank. this time it turned out to be an extra 40 miles to the tank tanking the total to 440 miles before the low fuel light appeared. At this point I didn't care what was causing the increase in mileage I was just happy that after 4 years of owning this car it was finally paying me back. I again filled up the tank until it was brimming - this time with Shell V-Power Diesel. This was on Saturday 9th August 2014 - I was on the way from Accrington to Central London. I was using the cruise control travelling between 70mph and 80mph - 2000rpm to around 2300rpm. I managed to get 499 miles out of the tank according to the odometer it equated to 49.8MPG. I think it is down to the use of cruise control (mainly), along with the engine oil, zx1 treatment and the diesel fuel treatment. I'm finally now enjoying high mileage - I'm seriously chuffed by how well things have finally turned out. I've lived with 300-340 miles per tank for far too long having done 15,000 miles a year, I know I've been hemorrhaging money. I hope this post made some sense. I understand that many of you have suffered from low mileage issues, maybe this may or may not help. I will try to continue to update the progress being made - I hope this improvement stays forever. Thank you for reading.