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I always assumed to try to drive in as low a gear as you can, low revs, without the engine labouring to save fuel, steady acceleration, foot off the accelerator and just gentle pulses when you can.
But, today I put the dashboard to instant fuel consumption out of interest on my shopping trip. 2021 1.6l zafira. It was great seeing 999.9m/gal with my foot off the accelerator and surprising how high the fuel consumption went when accelerating. But I was surprised to see that driving at say 40mph it was saying 4th gear was considerably more efficient than putting it in 5th where it would usually be with lower revs.
I'm guilty of nagging my wife about remembering we have 4th or 5th gears when the revs sound too high to my ears and I'd be in a lower gear. Seems as usual I may be wrong 😂
Any thoughts? Is it car specific? Are those gauges prone to be wildly wrong? Or Is it actually best to mainly use 5th gear in faster cruising times even though you're going fast enough to be in it?
All engines/motors & pumps will have a power curve and a sweet spot around the duty point where it is most efficient. Loading the engine above or below this will make the engine less efficient.
So yes, using the appropriate gear and not necessarily the highest gear possible will make the engine more efficient.
I was taught the same thing.
Subsequent driving has taught me the 'lowest gear possible and pulse the throttle' thing to be utter horsecrap.
The key is getting the engine to work as little as possible for the speed you are going. At, say 30, the lowest gear possible to keep moving actually results in the engine having to more work. Especially if you pulse & coast.
My 2019 1.5 octavia is generally most economical under steady power at between 1500 & 1900 rpm (ish). 40mph, 4th gear almost every time. Modern cars are designed to be more efficient when driven smoothly and the whole accellerate/coast thing is pretty much the opposite of this.
Turbo motor = a sweet spot in power and torque where the turbo is adding to the party just enough for efficiency, without thumping more fuel and air in.
Having just moved from manual 2.0 turbo diesels for the last 20 years to an automatic/DSG 1.4 turbo petrol, I am interested about how the gearbox and revs work in the auto. I have found that without me having to change gear, I am much smoother on acceleration and allow the gearbox to do it's thing. An extra gear helps - 7sp! It rarely labours, and as @seriousrikk says it sits often at about 1500rpm, just whirring quietly away.
Ok, cheers, that's interesting! I'll leave the dashboard showing instant fuel consumption for a while and try to change the habits of a life time 😣
Think your zafira will have a little gear up icon on the dash I'd you'll be more economical in the gear above, so just follow that.
I find on my Zafira B, that is is more usuful to watch the Revs that the instanteous MPG. the sweetspot for me is about 1500RPM current average MPG is at 52.6
No, gear up icon on this model. No gear icon at all actually 😂
I've never heard of the pulse throttle/high gear approach - instinctively it sounds like nonsense though!
OP: Does the Zafira have an eco teach setting? Some sort of visual display that gives you a %score (or similar) dependant on how eco your driving is? That's a good one to try and beat. Something like this in my car:
One of the reasons I was interested is the average mpg read out seems to be 35moh regardless of what driving we're doing.
Yesterday was a 300mile drive back up home on dual carriageway and main A roads without any hold ups, and for all the range went up considerably cruising at 60-70 the average mpg didn't really change.
No green score, just the ave mpg, instant fuel consumption, or range options
I use the throttle the other way round, keep it in a steady position just enough to maintain the speed I want. This is how the cruise control works when that's engaged. I get nearly 60mpg from my diesel van like this, though rolling along at 60 on my way too and from work undoubtedly has the most bearing on economy.
I would have said the current mpg display is going to change far too frequently to be of any good. What you need to do is reset the AVG mpg display for either each journey or for e.g. 100 mile blocks and see how it compares to different driving styles. Still a lot of variables though such as temperature, distance driven, whether the engine starts from cold or hot etc to be particularly useful, but still better than using the current mpg output.
You never said when you last reset the AVG reading. If you have not done that in a while even a 300 mile journey will not make a difference to it.
is the "low revs = efficient" thing not harking back to the days of old where the carbs just sucked in a set ratio?
Ah, thegingerone, not sure it's ever been reset! I'll go do that
I drove Glentress to Falkirk (52 miles) with bike in car (2020 Octavia estate 1.6 diesel manual) gently on acceleration and braking, at 62 mp/h max the trip average was 76mpg. I had previously thought max speed made not much difference to mpg (in a diesel car anyway)
is the “low revs = efficient” thing not harking back to the days of old where the carbs just sucked in a set ratio?
thats what i would have said. The ECU in a modern engine is going to deliver the exact (as near as it can) squirt of fuel it needs for each bang, depending on the map/tune.
The 999.9mpg under deceleration is due to the injectors injecting nothing at all.
i dont think air is controlled, rather just measured and accounted for? so running a lower RPM/taller gear will also reduce air intake per time/distance and affect the tune?
keeping the turbo spinning to force air intake to increase can only be a good thing, unless you are really tickling it along on the flat.
cruise speed on the motorway also makes a massive difference. i think it depends what your car is tuned to. I think they also accounts for the phenomenom of German cars up your chuff all the time. They might be tuned to cruise quicker, so are in a comfortable power band at a higher speed than say a French car that will be tuned to a peasantly 110kph or whatever the general limit is.
My OH has just bought an MX5 ND. It has a gear indicator which 'tells' you when to change up - it suggests 6th gear at about 30 MPH, which corresponds to about 1200 rpm. That cannot be good for the engine (2.0 184BHP) or the fuel consumption (which is pretty good, btw).
See lighter cars are where the slightly higher revs thing doesn’t always play out. That 2.0 an engine has a lot less mass to move than the smaller cc turbo lumps a lot of modern cars have.
For maintaining speed I expect 1200 rpm will be just fine, just change down to pick up speed (or do it really gently)
Though not as much of an issue with petrol, thanks to all the associated gubbins on modern diesels (EGR, DPF, VNT Turbos etc) though you can generally ride the torque, it's probably better to keep revving a little longer, so as not to end up with everything choked up in carbon like that galactic rogue Han Solo
In fact, of late my car has been more economic, but that's probably down to limp mode cutting boost and fuelling due to a coked up turbo, which makes for some particularly hairy moments when pulling out from junctions
Also low revs/high engine loads knock hell out of the DMF which ends up having to absorb the power pulses so they aren't fed into the gearbox.
Additionally lower engine speeds = lower oil pressure which isn't what you want when you mash the throttle and place high engine loads into the big end bearings.
Higher revs/lower loads = happy engines (apart from idling an engine which results in bore glazing due to low piston/cylinder wall pressures).
I am an absolute hoot at dinner parties.....