ZX TD Fuel Economy

Paul Thomas · Unread post by **Paul Thomas** » 15 Jan 2003, 13:32

I have a 1993 K-Reg 1.9 TD ZX Volcane.
I get somewhere between 40 and 45MPG, which seems pretty poor for a diesel (even Turbo) car.
I drive 23 miles each way to work at a fairly steady 55-60MPH.
What sort of economy should I expect and what can I do to improve it ?
I have had the car for 5 years and it's never been any better. When we first had it the garage sent the injector's off to be cleaned because of the poor economy.
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If it ain't broke ....... Leave it alone !

Unread post by **Jon** » 15 Jan 2003, 14:12

I worked out that I'm getting 38mpg (!) from my K reg ZX TD. I do 90 miles a day comprised of highish speed on the M4 then sitting in traffic getting in and out of Reading. <img src=icon_smile_sad.gif border=0 align=middle>
The thing is capable of much better though when driven carefully. I got to the Lakes and back on one tank (just) from Swindon and I was driving around 65 to 75 most of the time, it had to be doing around 50mpg.
Truly accurate MPG figures are difficult. I find that even when the tank is full, and fuel can be seen in the filler neck, after a short wait I can still get more and more fuel in until I lose patience.
Also worth adding that in my last ZX TD, I thought it was using a load of fuel, but turns out that the tank sender was telling me I had 1/4 of a tank when in fact there was nearer half. I changed the sender unit and that "improved" my MPG!
Driven hard, this engine is pretty poor on fuel, using full throttle causes overfuelling, and lots of smoke as a result. There are ways around this, and some of the conversions like the Van Aaken one actually solve this problem whilst increasing power.
However, at around 55mph and with a light throttle the car should be doing well over 55mpg. Allegedly!
Jon Wood
[email protected]

tomsheppard · Unread post by **tomsheppard** » 15 Jan 2003, 14:15

My K reg 1.9 non turbo BX is said to do 50 mpg. The ZX is, I believe heavier.Allowing for , say 10% due to manufacturer's optimism, well pumped up tyres, polished bodywork, dragless brakes, 300Kg of toolbox (well it is a Cit!) and fair wear and tear, I'd say that ain't bad for a ten year old car.

Simon Canfer · Unread post by **Simon Canfer** » 15 Jan 2003, 15:42

I had a K reg 1.9TD and drove it from 113 to 160k miles. It averaged 50.5mpg, that was mostly commuting on A-roads.
I now have an R-reg, 56k miles and it has averaged 47mpg.
I put the difference down to the later cars being heavier (more safety equipment); the later car has a Lucas pump where the K reg had a Bosch; and of course the mileage. Maybe 56k isn't quite run-in!
Higher tyre pressures help; (all the above figures are on Michelin Energy tyres)
This is an old-tech engine now so don't expect wonders. Diesel car got low-40s mpg too in their road tests as far as I recall. Console yourself that the petrol version would be worse still...
Simon Canfer
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Paul Thomas · Unread post by **Paul Thomas** » 15 Jan 2003, 18:29

I know all about petrol vehicle economy, my other vehicle is a Land Rover Discovery 3.9 V8i (12-13 MPG, now runs on LPG giving me 32MPG equivalent !)
I notice some of you are still getting 50 MPG though !
What am I doing wrong ?
I notice the turbo start to whine at 2000 Revs, it doesn't seem to have kicked in at 55 MPH as it is still only at 1800 RPM. Would this be a more efficient speed to go at then ?
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If it ain't broke ....... Leave it alone !

Simon Canfer · Unread post by **Simon Canfer** » 16 Jan 2003, 15:53

Well I wouldn't like to say what the best engine rpm is the most efficient, but I have read that the turbo can actually increase efficiency. Probably due to excess air and so you're more likely to burn all the fuel that's injected.
There are so many things that affect economy; Your Mileage May Vary as they say...
but here are a few things I keep an eye on, for what they're worth:
brake calipers "free" and not corroded so they drag;
tyres inflated at least to recommended pressures;
semi-synth or full-synth engine oil;
clean air filter;
clear intercooler fins;
cold-start device (on injector pump) is completely off when engine warm;
...and give it some hard acceleration every now and again in 2nd/3rd to the redline to clear out the soot.
To qualify my "50mpg"; I do mostly trips of 25 miles; so similar use to you. I simply try to put as little "load" on the engine as I can, i.e. not allowing it to labour at 1500rpm but on the other hand keeping below 3000rpm most of the time.
Do you have an MOT smoke check result? Might show if your pump is over-fuelling. Mine was 0.3

I did get my injectors cleaned at 148000 on the old car; they were in a state and needed new nozzles. Not that I saw any change in economy!
Simon
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Guru Meditation · Unread post by **Guru Meditation** » 16 Jan 2003, 20:27

Only filled up twice since I got the car. First time I calculated my economy to be 36mpg (<img src=icon_smile_shock.gif border=0 align=middle>35l in 277mi<img src=icon_smile_shock.gif border=0 align=middle>). Second time I filled up I got 31mpg (<img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_angry.gif border=0 align=middle>46l in 314mi<img src=icon_smile_shock.gif border=0 align=middle><img src=icon_smile_shock.gif border=0 align=middle>) however I think I may not have fully filled up both times. My fuel gauge seems to be dodgy-doesn't budge from above full for 100 miles then between 100 and 200 miles plummets to under half.
I know I definately filled up to the brim this time (I have the diesel pouring out of the tank to prove it (oops-daft I know but I'll get used to this diesel lark, sorry bikers etc I can assure you none was leaking from the car as I drove off). After the first time the pump cut off I got another 15-16l in all the while constantly cutting out if I let the pump flow more than 1/4 stength, so I am praying that I hadn't filled up fully last few times as I'm going to set the car on fire if it is only doing 35mpg!!!!!
With the driving I do I expect to get around low 40s. That'll be me happy s'long as I get my low 40s.
Guru Meditation

jeremy · Unread post by **jeremy** » 17 Jan 2003, 00:38

I just wonder if you have a fuel leak. We bought a 1.9 non-turbo zx (94) at the end of last year and as is our habit we filled it right up. It appeared to be doing about 20 MPG and on looking underneath the bottom of the tank was wet with fuel. I took the back seat out and inspected and replaced the clip on the visible vent pipe. there was fuel everywhere and it was collecting round the outlet pipe unit and the gauge unit.
This made no diffence so I changed the seal round the gauge unit - still no difference and I then found towards the front of the tank there is another smaller vent pipe which connects the filler pipe with the top of the tank. I duly cut a small hole in the floor, levered of the lip - and - there was split on the back side of the pipe , about 1 inch long.
I replaced this pipe and on mixed driving we have had 45 mpg, which has dropped to 35 on all short town driving. - Not brilliant - but much better than petrol and its quite a big car and quite heavy.
As a matter of interest I was getting just over 46 from my TD BX estate last year on holiday, driving it quite enthusiastically. On ordinary runs I recon on about 40 (5 miles to work - usually one way in traffic and not trying to be economical. On my return from holiday I achieved some staggering figure as I had to go at a more reasonable rate in the inside lane as the brake light switch fell apart on bank holiday sunday night. I would have said it was well over 50, as the thing was not full when I left and ran to 535 miles before I filled up (46 or so again) but I'd been going to work for about 2 weeks after my return. The BX is relatively young for its type at 185 k miles.
jeremy

Simon Canfer · Unread post by **Simon Canfer** » 17 Jan 2003, 12:30

Just a thought; you might want to get the injection timing checked out by a diesel specialist. Apparently it's a quick job. If it's too retarded economy will suffer.
Simon
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Guru Meditation · Unread post by **Guru Meditation** » 17 Jan 2003, 22:25

Thanks for the advice. I'm going to check very carefully for any leaks (haven't noticed ANYTHING under the car tho, apart from the oil leaking from my sump plug since I changed the oil <img src=icon_smile_sad.gif border=0 align=middle>). I am also gonna bung a sh*t load of Redex Diesel in next time I fill up. My car has a 'whistle' under load I suspect is an air leak in the induction system, whistling as air rushes in through it under load but could this hurt economy? Should cause under fuelling if anything???
Could it be pump timing? I seem to have normal power and no smoke other than when you would expect it etc. If there are no leaks and I don't get better economy I will check it out. BTW I don't thrash the life out of the car either <img src=icon_smile_wink.gif border=0 align=middle>.

jeremy · Unread post by **jeremy** » 19 Jan 2003, 17:27

I think you turbo air leak might affect fuel economy as it will slightly reduce the boost pressure available at a steady speed and effectively slightly reduce the compression.
Incidentally these leaks were discussed a few days ago on this board. A search would be worthwhile.
jeremy

Alan White · Unread post by **Alan White** » 26 Jan 2003, 02:20

Seems to me like your geting average mpg for normal driving. My ZX is the first diesel car I've ever owned and it was quite a novelty when I first got it to see how many miles per gallon I could get. Try keeping the revs between 1500 and 3500, if you have switched from petrol to diesel it is very difficult to get used to changing up a gear so early because a petrol car would labour if you changed up at 3500 rpm. Thats the beauty of diesel engines having so much torque, you can change up so much earlier. Don't put your foot to the floor too much - this is a temptation when you feel like you need to press a bit harder - but all this does is wastes fuel. And if it's just you in the car most of the time try running on less than half a tank as the extra weight of a full tank will reduce the economy. And don't forget that diesel engines are far more economical in the summer than winter because the warm temperature thins the fuel which is just like any other oil. You will really notice the extra mpg for this reason alone. Maybe you could also add a can of Wynns diesel injector cleaner at every service - I have for ages and my old ZX has done 183,000 mls and doesn't smoke a bit.

David W · Unread post by **David W** » 26 Jan 2003, 03:53

Alan's advice about driving style is very important.
Some folks will cane a diesel to make it perform in the same way as a petrol. With the Xantia more than the ZX this can get you down to 35mpg...that really makes folks grumble.
If you can drift about under 2500rpm most of the while the consumption will be excellent. Just allow the strong torque to pull you along when performance is required and then go back to high geared drifting.
Our 9yr old ZX TD at 110,000mls averaged between 47mpg and 50.5mpg over the first few thousand miles when we bought it late last year. Almost all main road and rural minor roads, no motorways...driver only, nothing in the boot.
My Xantia TD of the same age/mileage averages about 43.5mpg drifting about locally (the same short runs that had my petrol BX19TRS down to little over 25mpg). On longer holiday runs it does about 47.5mpg.
David

Dave Burns · Unread post by **Dave Burns** » 26 Jan 2003, 15:19

Well I can't fault what Alan White says about driving technique in the quest for best fuel economy from a diesel, I don't however agree with what Alan says about summer conditions favouring the diesel from an economy standpoint.
Firstly the fuel is heated by the hot coolant at the filter, so shortly after starting a cold engine the fuel should be at very similar temperatures, summer or winter.
Plus the diesel burns the same amount of fuel at cold or hot start, summer or winter, except that the fast idle will stay on slightly longer in winter.
The actual viscosity of the fuel, providing it hasn't waxed, pales into insignificance when compared to the ferocity of injection, the pump will hammer the same amount of fuel in regardless of temperature.
Secondly the cold damp winter air actually favours the diesel engine, because its much denser than the warmer and drier summer air, it expands much more when heated, the high compression ratio of a diesel makes much more use of this extra expansion rate than a petrol engine and so is much more noticable.
I often experience differences in performance from my diesels in the summer months, if you drive to work especially in the country and over the same route daily, you will notice the car often climbs hills better in the very early morning or late evening for instance, this is because the air is colder and denser at those times than during the day.
Dave