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I own a 1996 306 diesel and although I drive it hard, am not impressed by the fuel consumption compared to friends of mine who make statements such as "I can get 700 miles from a tank in my one etc etc..." I rarely get much more than 400-450 miles from my tank but reckon I should get more. What can I do to improve fuel economy without changing driving techniques?
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Any particular driving techniques you do not want to change?
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Buy a lighter car with a smaller more economical engine
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The technique I have used when I have had to stretch the last bit of range out of a tank of fuel is to imagine a raw egg attached to both the throttle and brake pedal... and try to drive at the most Aero efficient speed(back in the 50s M-benz autos came with a graph showing speed vrs range and it was interesting to see that my dad's Gullwing had a best range speed with the 3.25 rear end of 58mph and the sedan with the similar engine it was about 38mph) say 50mph...
It is amazing how much these techniques can add to range.
Randolph Lee
Nantucket Island, U.S.A.
I live in my own little world, but it's ok, they know me
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Matt
You say that you drive the car hard but are you sure that you aren't absolutely thrashing the living daylights out of it? The 306 has a 60 litre tank and if you get 450 miles that equates to 34mpg.
I've had a 306D and a ZXD (same mechanics) and almost never managed to get below 43mpg. They are low geared (about 22mph/1000rpm) unlike the TD which is geared to about 27mph. Really caning the atmo diesel will not give the best economy.
Unless, of course, it has a mechanical fault.
Ian Cook
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Might be worth doing a few simple checks such as getting the timing checked and adjusted if necessary, and putting some Redex or Miller's Diesel Power Plus additive in the fuel to give the injectors a clean.
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Matt,
I regard 42mpg as about the minimum for this engine range as well. My Xantia does between 42-47mpg, and it's a larger body to haul than your 306.
Many careful folks hover around the 50mpg mark and the highest I've heard from one of these I look after (in a BX) is 56mpg.
David W
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I agree with HJ - used to always get 42 mpg with ZXTD Estate,however driven.
I think the earlier XUD's - non-catalysed - could get considerably more, but since catalysts arrived - and Ultra-Low Sulphur Diesel - the later engines struggle both in performance and consumption.
My HDi 110 Xantia Estate seems to do 45 in 'general' use, driven fairly hard.
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Matt
I've found diesels very susceptible to useage. I had a HDi 406 on rent for a number of days recently, and for the first couple of days thought it was OK on fuel - high 40's. I brimmed it every night, and checked against the mileage. However, those were steady 'motorway' days.
It then had some back road use, including the A54 across to Buxton, and the economy dropped to about 38. Could be because it was the 90bhp version, and not that rapid.
Experiences of colleagues who've run pugeot diesels in the past has been similar - decent consumption if you treat them very gently, but as soon as you use the performance, the economy suffers to the point where they are no better than petrols. In contrast, there doesn't seem to be quite such a difference with petrols between motorways and back roads. Over a couple of years, and 50k miles my 2 litre Vectra averaged over 37.
Regards
John S
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In response to the original question, I got 37 mpg out of my Xantia TD whilst I had it. Drove it with a fair bit of welly - a lot of it up and down the Fosse Way between Bristol and Leicester so a fair few hills and 90+mph straight bits ;-) in between.
Experiences of colleagues who've run pugeot diesels in the past has been similar - decent consumption if you treat them very gently, but as soon as you use the performance, the economy suffers to the point where they are no better than petrols.
Have to disagree with you here - definitely true that there is a fair decline if you use the performance, but nonsense to say that a petrol driven the same way would be just as good.
My current petrol Laguna 1.6 does only 34 mpg - less mpg than a very old-tech TD engine in the Xantia.
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MMD
I think you've confirmed exactly what I said - diesels are not that good when they are not cruising steadily on the motorway. 37 from a Xantia TD hardly justifies having a diesel. Your Laguna 1.6 probably only does 34 because it's a 1.6 - the engine is working hard for the body weight. I'd would guess a 2 litre would probably produce the same performance for less petrol. I never worried particularly about economy driving in my Vectra, but it still averaged over 37, and the Fosse way wasn't unknown territory.
To go back to my original point, the fact was that, in my previous job, many of the diesels were averaging around the 40 miles/gall, compared to high 30's for the petrols. These were all high mileage company cars and the system was that business miles were recompensed on a pence/mile basis, rather than garage receipts. Petrol was recompensed at a slightly better rate than diesel, and combined with the extra couple of pence/litre to buy the smelly stuff some of the diesel drivers simply didn't see any benefit, and decided to do without the extra noise and diesel on their hands and shoes when they filled up.
Regards
John S
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Matt,
John S sums it up well on the useage issue. You do need to adapt a little with the diesel driving style, if you try and get a petrol type response by constantly flooring the throttle then waiting for the car to catch up then consumption will be high.
The circumstances where diesel consumption wins every time is the type of short journey use mine gets. Runs of one mile, four miles and ten miles are quite usual. With my old 1.9 petrol (auto-choke) the consumption could be around 26mpg with this use. Drifting round on the sme runs with the TD Xantia produces the 42mpg minimum I mentioned. And it's not doing so much damage to the engine as a petrol on the warm-up cycle.
David W
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Ambient temperature may be important.
When I got my new Corsa 1.7 diesel I kept a record of its mpg for a while and I sem to remember that hot weather (or as as hot as it gets here anyway) made a noticeable difference - to the extent of about 2 or 3 mpg.
It makes sense, in hot weather the bearing grease thins and the warm-up phase is quicker.
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Thanks guys-I guess you're right I should slow down a bit or get a TD which would suit my balls-out addiction to acceleration that my insurance company won't allow me to indulge in (only 20 years old). I should add that I notice a marked difference in the performance of the car occasionly-feels as though an extra 5-10 ft/lbs of torque is available on sporadically spread out dates. In fact I used to sell 306s and a major plus point of the TD is that it is only gp.5 insurance (non-turbo= gp.4 but 0-60 in 17.2 secs-hold on!!) Can anyone beat 0-60 in 12 seconds for a gp.5 ins. car? Golf mk.3 diesels in my opinion not as smooth/refined as the Pugger but can't argue with MPG. Lastly what do we think of mk.4 tdi Golfs and which one would suit me best considering my age and the previously mentioned obsession with acceleration. Would be sad to exchange a car that I still reckon handles better than anything else I've driven-passive rear-wheel steering helps (did you know that mech-heads!)
Many thanks guys-great forum and occasionally very entertaining!
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Yes but the warm weather also reduces the density of the air going into the engine and thus reduces efficieancy, I think! One effect will almost cancel the other.
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A turbo will work better with colder air as the air is denser.
But does this really effect mpg. It will make a diffence with power but normally aspirated diesels (like the 306) usually have a similar mpg to those that are turbo charged
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I had a 306xtdt - only once broke the 500 mile per tank (creeping round the M25 at a steady 30-40mph) before the warning light came on (which I think means 2 gallons left).
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My old 405 1.9 TD returned 42-45 mpg on a mix of roads, no matter how 'pushed'. My 406 HDi 110 gives 44-47 mpg under much the same circumstances. Usable motorway cruising speed is much the same as my previous 2.0L Mondeo petrol, although you sacrifice acceleration, of course. However, the Mondeo never returned more than 33 mpg whatever the circumstances, and was often under 30.
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Simple, change driving technique and the economy you seek will soon appear. Example, VW passat estate driven like a wild animal 37mpg; steady, slow accelerating and controlled driving, keeping under 70mph, up to 52mpg on motorway. All depends on how fast you want to get to places!
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My previous car, an F reg. Pug 309, used to return 50 mpg. The 306 is the direct replacement (but with cat?), so I would think that the reduction must be due to the cat and the right foot, with fuel type as a contributor.
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I've had the cat taken out when the exhaust was replaced-apparently it's not necessary with a diesel?? The right foot is definitely to blame...
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Matt,
So you're never going to try Randolph's excellent "egg" method then?
David
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Thanks David. Although it sounds like a lot of fun (?) I think I'll probably stick to the tried and tested "use the accelerator pedal as an on/off switch" method!
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Thanks David I was starting to wonder if anyone had noticed my addition to the thread... In the first heyday of 'mileage runs"
in the US the top champ was named "Balloonfoot Bodine" and he used (With several others such as rock hard as thin as he could fit tyres etc etc) the additional technique of shutting off and freewheeling down all hills...
BTW does anyone know when those oh so useful (esp to students attempting to get every last mile per £ out of their motor) Range vrs speed graphs vanished from auto handbooks?
Randolph Lee
Nantucket Island, U.S.A.
I live in my own little world, but it's ok, they know me
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Although having read this thread you may not believe it a reative of mine was so frugal with fuel that he used to turn the engine off to freewheel downhill. His downfall came when he had to swerve to avoid a hazard and the steering locked - he ended up upside down...muppet.
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Turning the engine off when going downhill will make absolutely no difference to the fuel consumption on a diesel, compared to leaving it in gear with your foot off the throttle. This is because the fuel will be shut off by the injection pump governor as soon as you take your foot off the throttle.
If you try turning the engine off while going down a hill, in gear and with your foot off the throttle, you will notice no change in the engine braking you feel, because nothing is changing on the engine. (Except maybe if you had the aircon on and turning the key also turns the aircon off.)
I suppose there might be some advantage in freewheeling in neutral with the engine off, but only if you could safely use the extra speed gained going downhill, after you have reached the bottom of the hill.
Mike Humpherson.
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MH
Turning the engine off makes very little difference on petrols either, as most injection systems have overun fuel shut-off when the engine is on a closed throttle above 1500 rev/min.
Freewheeling in neutral is a dangerous practice though - you haven't full control of the car.
Regards
John S
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Interesting, although the car involved was pre-fuel injection and it was clearly a dangerous practice as he ended up on his head!
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Mike
Only one snag with going downhill in neutral with the engine off and that is that you will lose the servo assistance on the brakes.
Doh!
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Er, not necessarily, Brian. I think most diesels have an engine driven vacuum pump for the brake servo as there's no depression in the manifold (no throttle butterfly).
BTW, apologies to your daughter (other thread). I try not to upset people I don't know! ...if you undertsand what I mean ..or have I just made it worse? ...oh, put the shovel down, Cooky!
Ian Cook
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Ian
No apologies needed, we don't subscribe to political correctness and the compensation culture.
ATB
Brian
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"Er, not necessarily, Brian. I think most diesels have an engine driven vacuum pump for the brake servo as there's no depression in the manifold (no throttle butterfly)."
Good knowledge once again but if the engine is turned off as mentioned this engine driven vacuum pump will not be particularly efficient!
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It doesn't do a lot for the power steering either!
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Please dont think I was serioiusly advocating freewheeling down hills with the engine off! I was just musing over whether it would help your mpg or not!
Mike Humpherson
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I recall that the best rpm at which to run an engine, for efficiency, is that at which maximum torque is produced. This is a sharper curve for petrol than diesel engines but it should be possible to find out what that rpm is for any particular engine
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Absolutely correct - these "max torque" speeds are typically 2000rpm for diesels and 4000rpm for petrols.
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I recall that the best rpm at which to run an engine, for efficiency, is that at which maximum torque is produced. This is a sharper curve for petrol than diesel engines but it should be possible to find out what that rpm is for any particular engine
Whilst in principle this is correct, not sure that its totally the case.
Modern diesel engines can have quite a peaky torque curve, eg take a look at that for the TDCi in the Mundano.
The diesel does tend to have an acceptable torque at lower revs than the petrol though, and this may be over a wider rev band. Like the piece of string it all depends.
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I found the answer to my post (above) and put it elsewhere on the site where it has not been replied to by anybody (yet)! The value of Max torque for each engine and the rpm at which occurs are listed in the technical section of Wh*t Car every month!
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Surely if you 'thrash' a diesel and petrol engine car, the diesel will still be the most economical of the two?
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