Author Topic: What MPG are you getting from your Mk1 Honda Jazz ?  (Read 201280 times)

guest4871

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #285 on: December 24, 2018, 05:17:45 PM »
Interestingly the Compression Ratio on the Mk3 is 13.5:1 - higher than the MK1 or MK2. I've often wondered if this is a possible reason for using higher octane fuel.

The mk3 is direct injection and the fuel can be injected during the burn and this prevents pre ignition effect, and means the fuel / air mixture can be a bit leaner as well.  The direct injection system was designed to be able to use higher CR and not have knocking because the fuel mist is injected near the spark plug,  IIRC The Mazda sky active DI system has an even higher CR of about 16:1.

The bottom line is that DI do not need higher octane fuel to prevent knocking, which is dealt with by the mechanism of the DI system, the DI injectors work at much higher pressure than normal port injection ( the mk3 has an electric lift pump in the tank and an engine driven fuel pump for the high pressure). DI injectors have the solenoid replaced by a piezoelectric mechanism to work at much higher speed to enable the extremely precise timing of injection.

http://blog.jepistons.com/gdi-gasoline-direct-injection-the-future-of-high-perf-engines

https://www.theengineer.co.uk/issues/24-october-2003/perfect-piezo/

Am I right in thinking this does not apply to the Mk 2?

PS Culzean - Many thanks for all your posts in 2018 (and before!). You are an inspiration to all of us who listen to your sage advice. A Merry Christmas to you and yours.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #286 on: January 18, 2019, 07:30:54 AM »
Just filled up this morning. It wasn't a huge fill up but as I have a trek into Edinburgh this afternoon I thought I had better fill up, just in case. I had covered 325 miles since my last top up, fill took 6.2 gallons, returning 52.4 mpg.
Considering we are now into the middle of January I am really pleased with that figure. About 40% of my driving was around town, but I think the, so far, mild winter we are experiencing helped a lot. It is so mild here that the gorse is starting to bloom, and in some spots has been blooming since just before Christmas.

springswood

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #287 on: January 18, 2019, 08:34:08 AM »
Impressive Jocko.

I do wonder if the difference at lower temperatures is not so much to do with changes in the fuel and air but rather to the sensors in the exhaust taking longer to get up to working temperature. That might account for the way when I have to do very short trips my mpg plummets.

Anyone know anything about this?

CORRECTION
I found out the sensors include heaters to regulate their temperature so I was talking out of my hat, who would have guessed  ::)
« Last Edit: March 12, 2019, 09:18:08 AM by springswood »
"Indecision is a terrible thing"
Or is it? What do you think?

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #288 on: January 18, 2019, 10:07:26 AM »
I get fairly good mpg on my short hops, it is the first 10 miles of longer trips which depress my mileage. I have my heater set to cold, constantly. The only time I put the heater on is after the blue light goes out on longer trips. I have noticed, that on a cold day, if I put the heater on as soon as the blue light goes out, it often comes back on for a brief spell.

smilertoo

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #289 on: January 18, 2019, 10:30:44 PM »
Im hovering at 38.2, possibly because its all town driving except a small hop onto the M8 then off one junction later.

guest4871

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #290 on: January 18, 2019, 10:47:37 PM »
Just filled up this morning. It wasn't a huge fill up but as I have a trek into Edinburgh this afternoon I thought I had better fill up, just in case. I had covered 325 miles since my last top up, fill took 6.2 gallons, returning 52.4 mpg.
Considering we are now into the middle of January I am really pleased with that figure. About 40% of my driving was around town, but I think the, so far, mild winter we are experiencing helped a lot. It is so mild here that the gorse is starting to bloom, and in some spots has been blooming since just before Christmas.

I have the feeling that the basic specification for petrol changes from summer to winter to summer and is therefore seasonal as well.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #291 on: January 19, 2019, 10:23:42 AM »
I have the feeling that the basic specification for petrol changes from summer to winter to summer and is therefore seasonal as well.
Possibly, but I know that the car coasts further in the summer than in the winter. On my regular trips I do elongated gear changes. By this I mean that as I approach a junction or roundabout, instead of changing down right at the hazard I will select neutral, 50, 60, 100 yards early, and coast up to the point where I select the gear for the hazard. This saves me having to brake. I know exactly when to select neutral to arrive at the hazard at the required speed, but in the winter these points are considerably shorter than in the summer.
I think it is down to the tyres being cold and hard, the transmission cold and stiff, possibly even the road surface (there is a huge difference between wet and dry tarmac as well).
It takes at least 10 - 15 miles of winter driving before the car loosens up and my ScanGauge E begins to show my average journey mpg improving.
Another thing I make great use of is Deceleration Fuel Cut Off, where the engine uses no fuel at all. The ScanGauge E displays that too. Sometimes, depending on the vehicle speed, 5th gear doesn't give DFCO but a change to 4th does. Every little bit helps in achieving good mpg.

culzean

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #292 on: January 19, 2019, 12:59:12 PM »
The petrol is made more volatile in winter to evaporate more readily at lower temperatures - summer fuel is more dense than winter fuel which helps get better MPG in summer.  Google 'reid vapour pressure'.

« Last Edit: January 19, 2019, 04:35:15 PM by culzean »
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peteo48

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #293 on: January 19, 2019, 02:07:35 PM »
Just looking at these last few posts, this style of driving has real relevance to EV driving. I am sure if/when Jocko gets an EV he will attain significantly better range figures than most. I was out with my walking group this Thursday and my pal came in his 2014 Nissan Leaf. He employs a range of techniques to increase range and low throttle input is definitely one. On cold days, he warms the car up in the drive by sending it a message from his mobile phone. This means the initial warm up is achieved whilst the car is plugged into the mains. He then turns the heating off and puts it back on when he feels the cold. Helps that his car has a winter pack with heated seats and steering wheel.

culzean

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #294 on: January 19, 2019, 02:41:27 PM »
The electric car makers do the trick of warming steering wheel and seats rather than actually raising the general cabin temperature and blowing warmed air around as warming cabin up needs too much energy,  what do they do in summer, cool the steering wheel and seats ?
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #295 on: January 19, 2019, 02:51:58 PM »
I have been a steady driver for years, always trying for good mpg. When I was a company van driver they always remarked on my fuel efficiency. I could get twice the mpg of the worst driver.
It wasn't until after I bought the Jazz I decided to try for real and read up on Hypermiling. I don't go to the extremes that some of those guys do, I would never coast with the engine turned off, or remove the passenger side wiper and mirror, but I did get the ScanGauge E, and though I only use the Instantaneous mpg (something more modern Jazz displays show anyway), it has made me slightly more efficient as a fuel saving driver.

peteo48

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #296 on: January 19, 2019, 03:02:37 PM »
One thing I'm finding with the CVT is that I'm less certain of how to drive it to gain maximum efficiency than I was with the manual. Overall they are supposed to have the edge over a manual box but I find I am pushing it a bit harder than I would a manual to get decent acceleration - this may have something to do with the Atkinson cycle (about which I know a vanishingly small amount). On the plus side, the very low revs when cruising must save fuel on longer journeys. It's almost like a diesel in this respect - 2000 (ish) rpm at 65 - 70 mph.

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #297 on: January 19, 2019, 03:52:57 PM »
Can you set the on-board display to show Instantaneous mpg? That is a brilliant tool. Just adjust your right foot to compromise between required acceleration and best numbers.

John Ratsey

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #298 on: January 19, 2019, 05:59:49 PM »
The electric car makers do the trick of warming steering wheel and seats rather than actually raising the general cabin temperature and blowing warmed air around as warming cabin up needs too much energy,  what do they do in summer, cool the steering wheel and seats ?
I would have thought the solution is to use a combined aircon / heat pump which will be variable speed to provide the required output. Typically, 250W of electricity will provide 1kW of heating / cooling although the actual performance depends on the temperature difference between ambient and target. There might also be potential to divert cooling air that's been through the motoras warm air for the cabin.

One thing I'm finding with the CVT is that I'm less certain of how to drive it to gain maximum efficiency than I was with the manual. Overall they are supposed to have the edge over a manual box but I find I am pushing it a bit harder than I would a manual to get decent acceleration - this may have something to do with the Atkinson cycle (about which I know a vanishingly small amount). On the plus side, the very low revs when cruising must save fuel on longer journeys. It's almost like a diesel in this respect - 2000 (ish) rpm at 65 - 70 mph.
Short bursts of acceleration shouldn't have a big impact on the trip mpg. If you need to get the speed up then it might, overall, be better to do the acceleration and then let the engine drop back to the Atkinson cycle mode once up to cruising speed. I recall that when I had a Mk 3 Jazz I found that the car was keen to get to about 3,000 rpm whenever I wanted even modest acceleration - too easy to pull away from some traffic lights and find I was quicly well over 30 mph and above the speed limit. This might suggest that Honda figured out it was better to accelerate + cruise rather than longer slower acceleration + less cruising.

 If you have a standard trip you frequently do then you could compare the trip mpg for different driving styles. However, you need to do such tests under the same weather conditions. We've touched on temperature but wind is another big factor and a moderate wind can cause at least 10% difference in the trip mpg depending on if it's a head or tail wind.
2022 HR-V Elegance, previously 2020 Jazz Crosstar

Jocko

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Re: What MPG are you getting from your Mk1 Honda Jazz ?
« Reply #299 on: January 19, 2019, 06:43:49 PM »
Brisk acceleration is the best bet for fuel efficiency. Not wide open throttle but about 80%.

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