Doctor Diesel

Outlandish fuel economy?

Web02I wrote to you before when I had a Volvo V50, when I was concerned about poor fuel economy. Thankfully, it did improve with time. I have just changed it for another diesel car though, this time a Mitsubishi Outlander 2.2 automatic. Before parting with my cash, I did plenty of research and read reviews, not only in Diesel Car, but every other magazine as well. It would seem that, despite being a bigger engine (now detuned from the previous model) it was capable of getting over 40mpg and towards 50mpg. Over the three weeks of having the car to date, a brim to brim refill check showed my consumption to be 34mpg. The computer readout cancels every time you start the car and that reads around the mid-thirties too. My journeys are varied, but do include motorways at moderate speeds, and I was expecting better than the V50 that used to get 42mpg in winter and 48mpg in the summer. I have been back to Anthony Betts at Hemel Hempstead, who supplied the car. It has 19,000 miles on the clock, and they have checked it on their diagnostic equipment and found nothing wrong. I am used to driving diesels and had two automatics, albeit petrols, so my driving behaviour cannot be the total reason. I accept that automatics are not as economical as manuals, but you must agree that 34mpg is not acceptable in these circumstances. If the dealer cannot help, where else can I go? As the car has 18 months’ worth of warranty left, I cannot yet go to one of the tuning companies to see if they can get me more mpg. The car performs well in every other respect, and I like the automatic, despite your tester with the ASX not doing so. Suggestions please?
Tony Mead

If yours is a post-2012 car, then the engine and transmission is the same as that in our long-term test ASX, which happily turned in figures of 40mpg plus, and more, as you will have read. Of course the ASX is a somewhat lighter car, but even so you should be expecting 40mpg or more. But you do need to establish why you’re only getting 34mpg before you think of “tweaking” it with a tuning box or a software rewrite, as it’s no use tuning an engine that is not running correctly, as might possibly be the case. If you can’t get any further assistance from your dealer, I should try going direct to Mitsubishi UK customer services. In view of the fact that you bought the car second-hand, it also might be worth checking out the car’s history. Sorry that I can’t be more helpful at this stage.

Tony then came back and said that he had been back to the dealer and had been taken out by a technician, with him at the wheel, when the car had returned 44mpg on a motorway run. Tony wrote “He obviously has a technique in driving, because I have never even got to 40mpg on the motorway. He has satisfied himself that there is nothing wrong with the car, but has, however, given me some useful tips to help my mpg. One is to avoid using supermarket diesel as he has found that you get up to 8mpg more by using the main brands, and I will do this when I get the tank low enough. I drove over 30 miles later on normal and motorway roads and my average mpg came up to about 38mpg. He did agree with remapping as a reliable way of improving mpg, although Mitsubishi themselves do not recommend doing it. He was honest enough to say that, in the event of a claim for engine damage (with a tuned car), they do not have the facility to check it anyway. All this information was unofficial, but the guy in question has since left the dealership, which I knew was going to happen. I am now left in limbo, apart from the fuel supply option, I do not feel I have the answers I need. I am hoping the good Doctor can help here.

To which I replied…

I think I would go along with most of what “the man” at your garage said, and 44mpg on the motorway is a fair figure. I honestly don’t think it sounds as if there is anything wrong with the engine, and there’s a way to go before you think of tuning it. In any case, I reckon it would take you a couple of years or more to get your money back anyway. I’m not sure about getting as much as an 8mpg improvement with branded diesel over supermarket stuff, but it generally does have a superior additive package. Of course there is Millers’ Diesel Power Ecomax additive, on which I am very keen. Get a bottle of this (at Amazon it costs about a tenner for a 500ml bottle) and try it in your engine. Some people stick to using Millers with supermarket fuel.

But I’m wondering whether you noticed anything in particular with the way the garage man drove? Economical driving is all about smoothness and not wasting fuel by braking. You anticipate when you’re going to need to slow down and lift off the accelerator early, so you often need little braking. I think with an automatic vehicle, how you accelerate is particularly important, as automatics can then be very thirsty. You want the engine to be working at its peak torque speed, generally 1,500 to 2,500rpm, where it’s most efficient. You’ll find that at a certain steady accelerator position the car will accelerate to maybe 2,000 to 2,500rpm and then change up, dropping back to maybe 1,600 to 1,800rpm, and will stay in that gear to about 2,000 to 2,500rpm when it will change up again, and similarly right through the gears. If it holds the gears to higher engine speeds, lift off a touch, or if too early, give it a touch more. This way you’ll get into a high gear fairly quickly. You then want to try and stay in this high gear and not have it dropping down a ratio unless you really need strong acceleration. So try and anticipate hills, and try to avoid harsh acceleration. With the Outlander you’ve also got gear-change paddles on the steering wheel, so you might take a good read of the owner’s manual and experiment with paddle changes. When you stay in auto and “kick down” to overtake something, this is when it uses a lot of fuel and you might get a better result just dropping a gear with the paddles. Try all these things and see how you get on, and try reading The Extra Mile page for extra tips!

Thanks Doc – you hit the nail on the head! The garage man was using the paddles and I notice that my car gets into a high gear quite quickly. I’ve tried using the paddles more and overriding what the auto box thinks best and seemingly I’m improving my mpg. I will try your Millers idea too. As I said before, I would only consider a proper remap, not add-on boxes. I will keep you posted.

2 Responses

  1. Our auto diesel Outlander 62, does 41-43 on motorway trips at 68-70mph. It loves poodling when mpg rockets. e.g.using adaptive cruise and sitting on the back of an HGV i have got over 6ompg recording before I left the motorway after 24mile journey.

  2. Our auto diesel Outlander 62, does 41-43 on motorway trips at 68-70mph. It loves poodling when mpg rockets. e.g.using adaptive cruise and sitting on the back of an HGV i have got over 6ompg recording before I left the motorway after 24mile journey.

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