Improved fuel consumption - CDT

[andymc]

Pleasant surprise, this! Ever since I took ownership of this car in the latter half of last year, the one thing I hadn't quite figured out was how come its fuel consumption was noticeably poorer than on either of the other two. After a full service including new PCV filter, a change of tyres all round, a couple of shots of injector cleaner and new brake discs/pads/calipers, I would still generally only get somewhere between 480-500 miles to a tank with reasonably careful driving, while anything more spirited would cost me more again. My fuel consumption in this car has generally ranged from 38-42 mpg. I always fill to the brim for accuracy.

At the weekend, I was away on a long trip for a number of days and without being too specific, at one stage I had the car at higher than usual revs for the best part of an hour and a half, followed by a 35-minute crawl to cover the final couple of miles. Then it was back to normal, tending to the leisurely and with some stop-start for about 75 miles. Sure enough, when I went to refill after covering 235 miles from the previous fill it took 30 litres, which I worked out at a mere 35mpg. This was understandable given the nature of the preceding trip and the pattern of fuel consumption I'd had till then.

However, after that fill I noticed that the car was apparently being much more parsimonious than before, as the fuel gauge was taking longer then usual to reach the quarter-mark - to the point that I was starting to wonder whether it or the fuel sender might have developed a fault! I was doing closer to A-road cruising speeds (55-60mph) for a further 255 miles, with a few miles of urban driving, and the subsequent top-up only took 22.5 litres, i.e. 51mpg. Now this may not seem all that unusual to some of you, but even though the majority of my driving is extra-urban, and I have done longer trips at this sort of speed before, I have never come close to that in this car! Since then, I've covered another 125 miles and the gauge is still nowhere near the first quarter mark - I reckon there's at least 25 to go before that.

At the last service, I did ask for the EGR and exhaust manifold to be cleaned, but it didn't seem to make any real difference. I'm now wondering whether the mechanic may simply have forgotten (I know him well and there isn't a dishonest bone in his body), with the result that my piece of high-revving driving forced months/years of accumulated crud out for the first time in who knows how long. Either way, I hope this new pattern continues!

[lipsee]

I too keep a eye on my fuel useage..I have a diesel auto,,I get about 43mpg .I use about 35lts aweek..The car does a regular run from London to Woodhall spa and then onto Boston all told 360(or there abouts)I try to keep the tyre pressures at 34psi..I had the car serviced and it runs good,(but want to have EGR valve cleaned..perhaps get it done the next service)When driving I try to use just 2000 revs..which may seems not much but can still do 70 on MY speeedo**,Acc is slow but its a slow old mans car.If I remember I like too put my foot down to blow the soot out now and then..Oh yeah I use cheap Asda diesel which is not the best and once every two months fill with best shell diesel...In truth I am dissapointed with 43,I was expecting around 50..but there again it is an auto and I just love the gearbox...Regards ** its runs very slow ,,its about 5mph slow

[hawker]

I have a 2lt auto diesel which on a 220 mile run gave me 40mpg. had a 160 remap done and the mpg dropped to 37. which from a 160bhp auto seems ok. but reading some fuel figures from you knowledgeable people now iam not sure

[maxxpump]

I get between 35 to 45 mpg depending how i use it. I have the 160 remap and all the gubbins are cleaned and in good service! i reckon i could get slightly better mpg with a hotter stat fitted.

[andymc]

Yes, I had the benefit of marinabrian's input before I picked the car up, and the car got a replacement thermostat two or three months ago. Mine's a manual, by the way. Best I ever managed in this one before now was maybe 135 miles per quarter tank, but only because I'd made such an effort to do that - no driving above 55mph and no hard acceleration/overtaking etc. Usually it'd do about 125 miles per quarter tank, sometimes less. By contrast, having gone back to more normal driving patterns after the trip it's now on 149 miles since the last fill, and the fuel gauge still hasn't quite reached the quarter mark. At a guess, when that happens it'll have covered 160 miles or thereabouts.

I think by now I've done pretty much everything that will improve the car's running and/or fuel consumption. All I need to do now is get round to sorting out the non-cooling climate control and the car will operate as it should.

[Kh44nn]

That's really nice to hear but unfortunately for my cdti zt I get 32mpg

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Originally Posted by Kh44nn

That's really nice to hear but unfortunately for my cdti zt I get 32mpg

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I know I still have to get the thermostat sorted as my temperature barely goes above the quarter on the gauge. So there

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[andymc]

Well I had another chance to measure fuel consumption over a longer than usual journey. Had a 275 mile trip on Saturday, which I did at roughly 75mph for the first 90 miles or so and then around 80-85 for the remainder.

First fill to the brim after that indicated that I was getting just over 46 mpg, which I think is spot on for that sort of speed. On Sunday I took a more rural route rather than the motorways, which meant I was able to cruise along at 55-65 between villages and town, a couple of which were bypassed but most of which I had to drive through. It took me exactly 15 litres to cover 180.1 miles , i.e. 54.58mpg, which is quite an improvement over what I'd been getting up till about 10 days ago.

I reckon it's working fine now.

[Ken Lion]

Originally Posted by andymc

...and without being too specific, at one stage I had the car at higher than usual revs for the best part of an hour and a half, ...

That sounds like something some on here describe as an "Italian tune-up".
The friend I acquired my car from (he'd had it 10yrs advised doing this every once in a while.

[T-Cut]

Originally Posted by andymc

Had a 275 mile trip on Saturday, which I did at roughly 75mph for the first 90 miles or so and then around 80-85 for the remainder.

Properly warmed up I'd say. Did you happen to check the running temperature during the trip?

TC