Our a3 2.0 tdi went back after 3.5 years of mainly town driving. Computer over that time said 34.9 mpg. Brim to Brim said 33. This was mainly driven by my wife. In that time it had a few major issues fixed under warranty.

Oil consumption was 1L per 8,000 miles.

She’s since replaced it with a petrol bmw (arrrgh!) 116i (2.0L) that does 35 mpg on the same routes. The stop start effecient thingy just suits her (revvy) driving. She doesnt know or care to be honest.

On long trips it probably less eco but we genearlly dont use it for long ones (no boot etc).

So in retrospect – buy a diesel – change driving style, expect more repair bills and less stops at the pumps. Which is more “economical” depends on you, your miles, what breaks etc.

My point is that YOU need to change – not the fuel / car. Adapt to what you’ve bought.

I was told I was unsympathetic to the engine whilst doing a defensive driving course for work, as I was using the engine to slow. I was always told to change down in anticipation of slowing/ stopping so you can apply power quickly if needed and drive out of a situation. Apparently no, I should leave it until the car starts to judder, depress clutch and then brake!

I’d disagree, in a way. There’s a tad more load on the main/rod bearings during engine braking, in comparison with under some power, but those bearings should not see any wear from it if the engine is operating properly. Valve train gets a tad more wear, but it’s well within normal design limits. Engines are designed to work this way, not to be dragged down to below the idle control point (juddering) and then changed. The juddering is the engine being shock loaded at a point where oil pressure is at a minimum. Not clever.

Well, thanks for all the advice, some very interesting responses.
I’ll be trying out a few of the techniques mentioned and see if the MPG changes over the next few tankfulls.

Inbred456 – Member

Wasn’t the 2.2 diesel in the Omega borrowed from BMW.

No, that was the 2.5 6 cylinder, which apparently came with loads of issues as standard.
This one is the old GM/Isuzu unit.

molgrips – Member

Quite like the gentle nature of the power, but sick of changing gear all the time!

Well then don’t. Dunno what you are talking about but I always change gear much less in a diesel on a windy country road than a petrol. .
It’s a big heavy car with a comparatively torquey but underpowered engine – currently feel the need to stir it to keep it in the sweet spot of the rev range – I’ll try various techniques and see what works. Remember, I’m new to all this diesel malarkey.

As to the suggestions of spending more cash on tyres, air filters etc: I recently bought the car from a colleague’s husband for £350 – it’s done 250,000 miles and I’d like to keep the expenditure down as much as possible – I’ve changed the oil and filter and will look into energy saver tyres and a flash air filter when it comes time to replace them.
If it does go bang at least I’ll get £200.00 from the scrap man for it 😀

Right, get yourself a pre burn catalyst (effectively a ring magnet) an install it round the fuel line as close to the pump as you can. This will align all the fuel molecules into the same orientation and gives a more complete fuel burn- cost about £90.

That really made me laugh, thanks for that 🙂

Inbred456 – Member
Wasn’t the 2.2 diesel in the Omega borrowed from BMW.

As above, that was the 2.5. In Vauxhall tune, 137 BHP (IIRC) which was a tad underpowered for the weight of the car. Once up to speed tho, she did waft along. I had mine from new to 140k, no issues at all. Just disks and pads and servicing. Nothing else. Fantastic car.

Right, get yourself a pre burn catalyst (effectively a ring magnet) an install it round the fuel line as close to the pump as you can. This will align all the fuel molecules into the same orientation and gives a more complete fuel burn- cost about £90.

Serious?

RS – right.. well there are good and bad diesels, can’t say which kind you have but the distinction was even greater ten years back 🙂

My point is that YOU need to change – not the fuel / car.

Both. Diesels are more efficent, this is a fact. You’re not comparing like with like by comparing a petrol with stop start to a diesel without.

As for tyres, because energy savers last far longer than normal tyres, they are actually cheaper ime, and then there’s fuel saving on top. They might last 50k miles or more. However if you have an old Vauxhall with over 200k miles on it’s probably not worth it as the car itself may not last that long 🙂

I’d be cautious about sticking too many additives in diesel as I’ve read that it can strip a coating off the engine. Using a premium diesel every few tanks has the same beneficial properties but also the essential lubricants. I’m no expert, its just what I’ve read.

The additive that works is called 2-ethylhexyl-nitrate or 2-EHN, and it makes the fuel burn more readily. It’s got a very distinctive smell, and you can smell it in all those ‘power booster’ things and also the premium diesel.

Rusty, a couple of things. I drive an underpowered diesel-fueled lump of a car. Recently it started asking for 35mpg on a motorway and country roads. Too much for my liking.
I gave it some diesel, added Diptane (check my Pug post or google it) and after a few miles to mix it in the tank we went for a drive. Some 25 miles of twisty Irish country roads (R108 Drogheda to Swords), 3rd gear and over 3k rpm all the way. She cried at first, farted and coughed, then started singing. 3-3.5k rpm and she went like a stink. The consumption hasn’t gone up (and the road is properly twisty and hilly) compare to the flat and boring motorway, the car pulls better since.
The tyres – when I needed a set some 2 years ago I chose Milleniums, cheap and Avon-made, good enough for me. We happily spent 18 months driving all over the place including a blast from London to Poland with the boot overspilling. Several trips between London and Dublin followed. The front wore but the rear didn’t. As my Pug is FWD it probably affects the tyre wear. I considered Michelin Energy Savers but they were costly and… at least in the opinion of the 406 drivers’ forum, they give little grip in wet or slippery. So I found Uniroyals – proper rain tyres. The grip is immense, the ride supple, the noise – you have a radio for it.
Bottomline – just drive the thing, fix what needs fixing, change as and when required. Oil, filters, air pressure in the tyres, they all make a difference. Driving style? Not unless you’re a moron.
Enjoy!

I considered Michelin Energy Savers but they were costly and… at least in the opinion of the 406 drivers’ forum, they give little grip in wet or slippery

They are apprently much better now with the newer versions.

We have some from a year or two ago (not sure if they are the new or not, they might be) on the Prius and I have certainly not noticed any issues.

Top tip seems to be drive really slowly 🙂 This morning I had very little fuel and the petrol station at home is not convenient, but the one at work is. Stayed behind a lorry the whole way at 47mph and got 65mpg!

Ha! Moly with your green credentials, you should have been in that lorry and that would have neutralised your incremental carbon footprint for the day. Shame on you 😉 🙂

I should have been on my bike! I’ve attempted every morning this week to ride in, and failed each time. First four days I actually put on cycling gear only to have to take it off again. Usually a combination of too much faffing, ill-preparedness and extreme tiredness leading to over-sleeping or morning lethargy, however last night I was just putting a bit more air in the tyres and blew a valve, spare tube had multiple punctures 🙁

Interesting though that I’d normally get 51-52mpg on the same run, so going almost 50% faster on average only results in a 15-20% drop in mpg.

Drive a bit slower, 60mph will make a decent difference and unless you are going miles & miles it won’t take that much longer. You’ll probably arrive more relaxed too.
Look further ahead – no point accelerating if you can see a queue/roundabout/sharp bend ahead.
Slow down earlier on the approach to roundabouts/traffic lights. Let the car slow down, rather than driving at the same speed up to the obstacle & then braking hard.

I have started doing this on my commute and fuel consumption has gone up loads. Managed this on the way home from work last week (60 miles):

If you could run the engines at high revs constantly, diesel and petrol engines would give you similar power and efficiency. However, because you spend more of your time driving at less-than-optimal revs, that is where the diesel gives you the better performance.

Has anyone had their diesel engine re-mapped? Interested in experiences.

If you could run the engines at high revs constantly, diesel and petrol engines would give you similar power and efficiency

Not entirely sure this is true. Diesel has more energy in it per litre, and also diesels have much higher compression ratios which results in greater thermodynamic efficiency.

They would be closer if you ran at high load, because petrol engines run more efficiently with the throttle wide open. It’s inefficent to have to suck air through a tiny hole.

Incidentally VW’s FSI and TSI engines are direct-injection petrol engines meaning they don’t use a throttle (as much, if at all) – they slow the engine down by simply injecting only a little bit of fuel directly into the cylinder and cleverly making sure it ends up near the spark so it ignites.

Has anyone had their diesel engine re-mapped? Interested in experiences.

Had my Leon 2.0 TDI (PD) remapped a couple of years ago. Fuel consumption is roughly the same (if not slightly improved) but a lot more responsive in gear. I think the key is that you can accelerate up to speed more quickly.

As mentioned, a few MPH slower can make a significant difference to the MPG as can the usual suggestions of turning of the air-con, ensuring your tyre pressures are correct (or even a few PSI over), removing the roof-rack, and emptying your boot of unnecessary junk.

It gets to be abit of a game. More interesting than speeding tickets. -I’ve done with those.
I’d vouch for the lorry tracking. Only on quiet motorway in bone dry conditions mind. If you are sensitive to it, you can feel the draft from about three lorry lengths behind. I averaged 73MPG on a 350 mile round trip last year. Used about 1/3 of a tank full. Moderate gap, about “one chevron”, so I wasn’t being too loony.

Old Focus 1.9 TDCI with 150K miles.

you can feel the draft from about three lorry lengths behind

I’d like to point out I was NOT slipstreaming the lorry, merely not overtaking it thereby giving myself an excuse to drive at 47mph.

molgrips – I use the Nokian WRG2 over here. Simply the best tyre I have used. Perfect for UK winter as works very well in the wet and dry as well as snow and ice. I noticed the improved MPG too over Xmas.

Obviously they will be swapped over with my summer tyres soon but keeping them on for the time being. Simply amazing feedback on wet and slimy roads.