Clubjazz - Honda Jazz & HR-V Forums
Honda Jazz Forums => Honda Jazz Mk3 2015 - 2020 => Topic started by: Sidot on January 15, 2020, 10:23:03 AM
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A little advice if I may ask please.
It's about miles per gallon again I'm afraid.
I have Jazz 1.3 CVT new car August 2018.
Collected 21.8.2018.
I keep a "petrol book ".....always have, mainly for MPG comparisons.
I'm a senior citizen and drive carefully and consistently trying to achieve maximum efficiency.
Last year at this time my mpg was 33.4.
This year it's just been measured on fill up at 29.0.
Nothing changed and car recently serviced.
Any ideas why the poor mpg ?
Thank you.
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These seem very low figures - I have been consistently getting above 50 mpg over 4 years and 38000 miles, but that's in a rural area with a number of long trips, eg 800 miles last week. Are your journeys mostly very short, or with frequent stop starts? If so, I don't think the drop from one year to the next is significant.
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What MPG does it show on the car display ?
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Hi Sidot. I've got the same car as you. On other threads I've remarked on the huge range of mpg figures I have got on this car and my previous manual Mk2. As you can see from my avatar my current average mpg is a tad over 45 mpg. That said I have been as low as 35 mpg and as high as 57 mpg.
My typical drive is 1.7 miles to Sainsburys with a cold engine, an hour in the shop, then back home. I know that the car does about 28 mpg on that trip in cold wet weather. A few longer trips - 7 miles say - and the mpg goes up dramtically. A couple of times a year I do long trips - 200 plus miles - and that's when I get the best mpg.
I'd be looking at how many very short journeys in cold weather I did. If you don't do that type of motoring then your figures seem very low and I'd want a mechanic to look at the car.
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A little advice if I may ask please.
It's about miles per gallon again I'm afraid.
I have Jazz 1.3 CVT new car August 2018.
Collected 21.8.2018.
I keep a "petrol book ".....always have, mainly for MPG comparisons.
I'm a senior citizen and drive carefully and consistently trying to achieve maximum efficiency.
Last year at this time my mpg was 33.4.
This year it's just been measured on fill up at 29.0.
Nothing changed and car recently serviced.
Any ideas why the poor mpg ?
Thank you.
I wouldn't worry too much about the difference between 33.4 & 29 (that may be within the error band for the calculations), the real issue is that both figures are abysmal ! I just go by the car's computer, which typically gives me Trip A values around 55mpg over a mixed bag of in-town and open road travels, with Current Drive values as high as 70. Even allowing for the inaccuracy of the computer I'm happy with those figures.
It's tricky to try to diagnose your problem remotely because there are so many variables, but I'd recommend setting the infotainment screen to show the Current Drive to give an idea of just when you're using lots of fuel. It's surprisingly sensitive, and whilst not 100% accurate it does help in driving efficiently. Some thoughts:
Driving style. Obviously a heavy right foot is bad, but do you follow the green/blue lights on the instruments to prompt efficient driving? Not sure how that works with a CVT, but with a manual box you can get into 6th at a surprisingly low speed.
Geography; do you have lots of hills? I have a supermarket about 2 miles away up a fairly steep hill. The Current Drive display will show between 20 & 25 on arrival; on the return trip it's usually 80 or 90. So geography is important, especially on short journeys from cold.
Speed. I've been doing some longish trips west-east & return recently (A303-M3-M25-M20) with the cruise control set at the speed limit (so actual speed around 65), and I've found the stretch of 50mph limit through the M20 roadworks has a big effect on the Current Drive figures: typically 55-60mpg on entering the roadworks, 65-70 on exit a few miles later. Obviously if you can drive everywhere at a steady 40mph that'd be even better!
Weather. On my east-west trips, I find mpg eastbound is always better than the same route westbound. The only logical reason I can think of for this is the prevailing SW wind might be a factor.
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Many short journeys where the car never warms up can badly affect mpg. So too does depending on your brakes instead of anticipation and slowing down without braking. I used to get those sort of figures with my 2 litre Volvo!
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Thank you all for your replies and observations.
I have never trusted the on board computer and find that the only true way to measure mpg is full tank to full tank divided into miles covered.
I do agree that 29 mpg is abymal. However I am driving the same as last year and always try to keep the green light on. I'm a senior so no harsh breaking. All cold starts and urban driving.
My previous Mk3 manual gave better results.
Maybe I should drive it a bit more positively rather than trying for economy.
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Maybe I should drive it a bit more positively rather than trying for economy.
Give it a try. The figures you are returning are terrible. The figure beside my avatar is my calculated average over 35,500 miles. The "fibometer" is really rather optimistic. Fuelly.com is great too, for recording your numbers.
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The on-board computer might not be that accurate but it should be consistently a bit optimistic so I just wondered if it was similar to your calculated figures ? This would confirm your manual calculations.
I use my 1.2 Mk2 manual mainly for commuting, 70 miles a day, mostly on dual carriageways and motorways and it never really drops below 55 MPG on the on-board computer, I accept the actual might be a bit lower.
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This would confirm your manual calculations.
I wouldn't doubt the manual calculations. They are so easy to do. I have been calculating and logging my mpg since 1978. First on paper end now on a computer spreadsheet. Before that I shared a car then had a car with a broken odometer. The speedo worked but not the odometer!
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I have never trusted the on board computer and find that the only true way to measure mpg is full tank to full tank divided into miles covered..
If you want the best accuracy you can get in calculating historic mpg then you’re probably right (although there are sources of error in the brim-to-brim method as well). But that doesn’t give you real-time feedback on fuel consumption, which is what the computer does. If you’re genuinely concerned about mpg - and that is what your original post suggested - then it seems unhelpful to ignore a tool that is fitted to the car specifically to help with that. As Basil says, you just need to keep in mind that the absolute values it provides are probably a bit optimistic, but you can still easily see when you’re using fuel heavily.
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real-time feedback on fuel consumption
For best real time feedback you want to have the display showing "Instantaneous mpg". This shows you when you are in Deceleration Fuel Cut Off mode and using no fuel and shows when you are saving fuel and wasting it.
My Mk 1 does not have that function, but I have fitted a ScanGauge E which does. It plugs into the OBD port.
(https://i.imgur.com/qV2N6DN.jpg?1)
I have it set to show Instantaneous and Average for the journey. I aim to keep the top number greater than the bottom, whenever possible. The beauty of the ScanGauge is you add a correction factor each time you top up, so it is more accurate than the "Fibometer". If it says I have used 6.8 gallons since last top up and the fill says 6.6 gallons you make the correction. I normally correct to half the discrepancy, so in this case I would tell it top up was 6.7 gallons.
I know, that on one steep hill near me I get best fuel consumption, in 5th, with my foot flat to the floor. It shows 32 mpg. If I change down to 4th I get 27 mpg and 3rd (which seems the right gear to be in) 24 mpg.
Since fitting the ScanGauge my mpg has improved sufficiently to recover the cost, and then dome.
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I realise it's easy to calculate MPG manually Jocko but when you have to enter details manually there's always room for human error, did I mistype that odometer reading or number of litres, easily done. I was just suggesting that the on board computer removes this chance of human error would be a useful comparison tool.
The ScanGauge data is interesting, I would never have thought it would be more economical to drive up a hill in 5th with my foot flat to the floor, does the engine management system then limit the amount of fuel supplied to the injectors ? I know nothing about how modern cars work.
Going back to the original question, was the 4.4 decrease in MPG over the same distance and time period as last year ?
Has it been significantly colder this year ? Have you checked your tyre pressures ? Did you do any longer trips in the same period last year ?
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I run my Jazz primarily in urban areas.. but teh OP's fourney length with a cold engine is going to end up withe teh exhaust never getting warm. Cue build up of carbon and ash deposits.
But teh issue is the catalyst. It will never get up to temperature despite being close coupled and will slowly block up. And teh plugs will be the same.
A 10 mile trip every week with revs in excess of 3,000 is required to burn off deposits.
It is likely that consumption will worsen unless teh car is occasionnnally driven harder.
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I'm convinced there is a lot in what you say madasafish. With this in mind I occasionally go the long way round to the shops giving the car a bit of a motorway run.
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I do agree that 29 mpg is abymal. However I am driving the same as last year and always try to keep the green light on. I'm a senior so no harsh breaking. All cold starts and urban driving.
My previous Mk3 manual gave better results.
Maybe I should drive it a bit more positively rather than trying for economy.
Perhaps the basic question is therefore why the CVT Mk 3 is giving significantly worse MPG than the manual Mk 3 you drove previously for the same route and driving conditions?
Does your CVT Mk 3 give similar engine speed behaviour to you driving the manual version? I drove the Mk 3 CVT for a year and didn't like the way it piled on the revs every time I applied more than very light pressure on the accelerator pedal.
I agree that cold engines and short trips give abysmal fuel economy. If it were easy to block off most of the radiator and reduce the flow of cold air into the engine compartment during the winter months then I would. My current work-around is that I normally leave the heater fan off for the first couple of miles to help the coolant warm up.
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I never switch to "Warm" until the blue light goes out.
(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQEVhee4AhbqklFdUy-0AJ5Mf2KdOt6CbUf31vpsvoKh8q8zcreCw&s)
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The GK3 blue light goes out ad 43°C, but the climate control turns on the fan some seconds before, I suppose at about 40°C and the air is quite hot.
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Quickest way to warm and engine is driving, not ticking over on the driveway. You shouldn't over-rev a cold engine but just pottering at low revs means it take longer to warm up - I once read that pretty much every engine does 25mpg when cold ... I used to block off radiator grill on cars, but they used to have big fans driven by the engine that were constantly rotating and sucking cold air through radiator matrix and blowing it over the engine, modern cars with electric fans you will never see the fan switch on in winter ( unless you are using aircon or climate control ), and maybe not even in summer unless in traffic and really hot weather ( unless using aircon )..
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I used to block off radiator grill on cars, but they used to have big fans driven by the engine that were constantly rotating and sucking cold air through radiator matrix and blowing it over the engine, modern cars with electric fans you will never see the fan switch on in winter ( unless you are using aircon or climate control ), and maybe not even in summer unless in traffic and really hot weather ( unless using aircon )..
In the pursuit of efficiency, some modern cars are now being fitted with electric shutters on the front grille to stop the entry of cold air such as Ford's 'Active Grille Shutter'. They are primarily to aid aerodynamics, but are also to help shorten warm up times.
Can you remember carburettor cars with a winter position for the air filter intake, pulling air from the back of the engine?
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Quickest way to warm and engine is driving, not ticking over on the driveway. You shouldn't over-rev a cold engine but just pottering at low revs means it take longer to warm up - I once read that pretty much every engine does 25mpg when cold ... I used to block off radiator grill on cars, but they used to have big fans driven by the engine that were constantly rotating and sucking cold air through radiator matrix and blowing it over the engine, modern cars with electric fans you will never see the fan switch on in winter ( unless you are using aircon or climate control ), and maybe not even in summer unless in traffic and really hot weather ( unless using aircon )..
If I turn left out of our drive , I then have a 1 mile drive on a twisty slow road up a steep hill (+100meters high) . If I had zeroed the trip before starting from cold , my MPG then reads 12 to 14mpg....
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Can you remember carburettor cars with a winter position for the air filter intake, pulling air from the back of the engine?
20 mpg was good in those days. Also, cars had no heaters, so travel in winter involved bulky clothes, gloves, and rugs for passengers!
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The ScanGauge data is interesting, I would never have thought it would be more economical to drive up a hill in 5th with my foot flat to the floor, does the engine management system then limit the amount of fuel supplied to the injectors ?
Climbing that particular hill this morning and I was thinking about your question. With a modern engine the amount of fuel burnt depends on the amount of air being drawn into the engine. The amount of air drawn in depends on the throttle position, but also on the rpm. Higher revs draws in more air for a given throttle position. My full throttle at low revs uses draws in less air than 4th or 3rd gear at higher revs and less throttle, therefore uses less fuel.
Unless someone knows otherwise.
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Also, cars had no heaters, so travel in winter involved bulky clothes, gloves, and rugs for passengers!
I have had cars from the early 50s on, and they all had heaters. Mind you, they were an optional extra on a new Ford in 1956.
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Can you remember carburettor cars with a winter position for the air filter intake, pulling air from the back of the engine?
20 mpg was good in those days. Also, cars had no heaters, so travel in winter involved bulky clothes, gloves, and rugs for passengers!
Not going that far back, I'm not that old!
Other half had a 1985 Renault Super 5 with the movable elephant's trunk attached to the air filter, you could attach it to a box around the exhaust manifold for winter.
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I used to block off radiator grill on cars, but they used to have big fans driven by the engine that were constantly rotating and sucking cold air through radiator matrix and blowing it over the engine, modern cars with electric fans you will never see the fan switch on in winter ( unless you are using aircon or climate control ), and maybe not even in summer unless in traffic and really hot weather ( unless using aircon )..
In the pursuit of efficiency, some modern cars are now being fitted with electric shutters on the front grille to stop the entry of cold air such as Ford's 'Active Grille Shutter'. They are primarily to aid aerodynamics, but are also to help shorten warm up times.
Can you remember carburettor cars with a winter position for the air filter intake, pulling air from the back of the engine?
Yes, cars had a lever or a hose that you moved to pull air from over the exhaust manifold. Also had engine coolant flowing around carburetor to warm it up or prevent it freezing when the air was rushing through vapourising fuel - I can remember during the harsh winter of 1982/3 when my Vauxhall would not start despite having a good spark and fuel, had a lightbulb moment and used her-indoors hairdryer on the carb, and it started ok - that was the year the daytime temperature went down below -20degC and stayed there for weeks, even colder at night.. had to do the hairdryer trick for weeks before starting car to get to work.
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The ScanGauge data is interesting, I would never have thought it would be more economical to drive up a hill in 5th with my foot flat to the floor, does the engine management system then limit the amount of fuel supplied to the injectors ?
Climbing that particular hill this morning and I was thinking about your question. With a modern engine the amount of fuel burnt depends on the amount of air being drawn into the engine. The amount of air drawn in depends on the throttle position, but also on the rpm. Higher revs draws in more air for a given throttle position. My full throttle at low revs uses draws in less air than 4th or 3rd gear at higher revs and less throttle, therefore uses less fuel.
Unless someone knows otherwise.
That makes sense, I didn't really think of engine speed being a factor.
What sort of revs do you get down to ?
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What sort of revs do you get down to ?
I'm not sure. I'll check it out the next time I am on that hill.
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What sort of revs do you get down to ?
I'm not sure. I'll check it out the next time I am on that hill.
Bear in mind the i-DSi engine is much happier and tractable at low revs than the later V-tec engines....
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What sort of revs do you get down to ?
I'm not sure. I'll check it out the next time I am on that hill.
Bear in mind the i-DSi engine is much happier and tractable at low revs than the later V-tec engines....
Fair point, I've not driven that version but I might change my technique and see how it feels.
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I can't get all enthusiastic about fuel consumption. The built in readout is accurate for my needs even if it is optimistic it tells me if my consumption is about normal for the type of driving that I am doing. Any sudden increase in consumption would warn me that something may be amiss.
The comments about wide throttle openings and high gears are interesting. If you open the throttle wide in a high gear you will kill the acceleration and the responsiveness of the engine and you will be using the wide open throttle to get anywhere for longer periods. Overtaking manoeuvres would take longer, dangerously so in many cases. Why flog an engine to death trying to climb a hill in a high gear? I am not convinced that driving in this manner is conducive to better fuel consumption.
On my 1.4 CVT I get a recorded 52mpg in the warmer months and 48mpg in the winter and I use the 'S' mode frequently.
Vic.
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The comments about wide throttle openings and high gears are interesting. If you open the throttle wide in a high gear you will kill the acceleration and the responsiveness of the engine and you will be using the wide open throttle to get anywhere for longer periods. Overtaking manoeuvres would take longer, dangerously so in many cases. Why flog an engine to death trying to climb a hill in a high gear? I am not convinced that driving in this manner is conducive to better fuel consumption.
The reason I have the throttle fully open is to maintain 40 mph. If I wanted to accelerate I would change down. If I want to overtake I use the lowest gear that will allow me to pass without having to change up, normally 3rd. The engine isn't being flogged at 40 mph in 5th. It is just slightly below maximum torque.
And as for fuel consumption, in the summer my dashboard display will show 60+ on a tankful and no lower than 54 in winter.
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What sort of revs do you get down to ?
1900 rpm. i-DSi has loads of torque down there. Something the V-TEC lost.
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What sort of revs do you get down to ?
1900 rpm. i-DSi has loads of torque down there. Something the V-TEC lost.
I agree, the I-dsi is like a little diesel compared to vtec..
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I had a mile trip to the supermarket, then after shopping, a mile home. The blue light never went out, but according to the ScanGauge E the trip returned 37 mpg.