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Old 07-30-2017, 06:14 AM   #1
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Disappointing highway mileage.

I am disappointed with my mpg on highway driving. Irrespective of what I try, I am struggling to better my highway mileage from before getting my ScanGauge. Back then I would just try and drive smoothly, not too fast and with a light throttle. I still use all these things but have included Pulse and Glide where appropriate and even engine on coasting. Nothing seems to make much of a difference. The main problems seem to be having to keep up with traffic, and the facts that the roads were all built in the last 30 years and as a result have no appreciable ascents or descents.
I have actually started coming off the highway, for one section, as there is a nice bit of single carriageway country road with several short steep ascents followed by long gentle descents. Using a bit of petrol for the steep climbs allows me miles of descents, at 300 - 350 mpg, with occasional DFCO parts (into tight bends) where the ScanGauge indicate 9999 mpg.
My biggest improvement in fuel consumption is, surprisingly, around town on the short trips.

Any other advice for highway driving?
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Old 07-30-2017, 06:27 AM   #2
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It's hard to beat the exponential cost of aerodynamic drag. Bottom line is every mile requires more energy the faster you go, twice as fast, four times the energy.
The more efficiently your car is designed as far as overall, it will not overwhelm the quadrupling of aero drag every time speed is doubled.

My best mileage, which approaches 120 (British gallons) is a deserted road with a 35-45 mph sped limit. Pulsing to 42, then coasting down to 20 or even 15, I can exceed 100 mpg fairly easily with engine off coasting. Leave the engine running and that mileage would drop by at least 30%, especially since idling is a total waste of fuel in this scenario.
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Old 07-30-2017, 06:35 AM   #3
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I find my best fuel mileage at speeds over 50 mph involves using my situation to my advantage. At one point in my local routes there is a major artery, built in 1957, that during the heaviest traffic days, will see 85,000 vehicles per day pass over the same spot in the same lane. About 1 vehicle per second for an average separation of about 85 feet, including the vehicle itself, or about 70 feet distance or less than two stripes at 43 feet point to point per stripe.

That's a 24 hour average, NOT A PEAK AVERAGE WHICH IS MUCH HIGHER.

Since, in that precise scenario, it is impossible to avoid being on someone's arse, and having someone all over yours, you realize a significant aerodynamic benefit, BUT ONLY AS LONG AS THE PERSON IN FRONT OF YOU DOES NOT HIT THE BRAKES, OR YOU RUN INTO THEM.

For those not familiar with this scenario, the fist time they are exposed, it can really be scary. I do it regularly and accept the scenario, to the point where it has become in integral part of my driving skill set, and it will get me 65 mpg at speeds that can approach a 60+ mph AVERAGE.

I can come closE to that average on deserted country roads ONLY by reducing my average speed by close to 20 mph.
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Old 07-30-2017, 06:39 AM   #4
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I have found similar things with small underpowered cars in the past, they tend to be geared more for town usage, and tend to scream a bit on the highways. I've always been surprised by cars with alot of power just how fuel efficient they can be providing the engine is still small, as you hardly need to use any throttle inputs and the engine is doing very little work.

I would trade up, get a quicker car with more power and a turbo is a must! Use the power to weight ratio to give you a good idea of performance and you'll get a good idea of your economy too, just make sure it's still a light car as weight is your biggest enemy. You will have slightly higher fuel costs perhaps, but you'll also have way more fun too!
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Old 07-30-2017, 06:50 AM   #5
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And yes, even in the above scenario, I use engine off coasting. I have no problem with my 1950 pound car when it comes to steering and brakes. The power steering and brakes are assisted. I would actually prefer NOT having that in the first place, windows as well and even two fewer doors would be OK. IN many of my local trips the PERCENTAGE of engine off coasting is as high as 40% of the time. In those situations it takes as far as 5+ miles for my engine to reach normal operating temperature, which I try to offset by using a block heater, even in summertime.

Without it the engine would be idling all of that 40% of the time and would really kill my mileage.

You will find that you reach a plateau depending on your personal dedication to efficiency and your willingness to make a serious effort in the regard.
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Old 07-30-2017, 06:54 AM   #6
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If they had ever brought your Honda into the USA, I WOULD OWN ONE. The 1.2 idsi engine in your fit was tested and found to be very close to the efficiency of the original CIVIC VX lean burn engine, which was an amazing piece of automotive technology.
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Old 07-30-2017, 07:10 AM   #7
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Quote:
Originally Posted by Draigflag View Post
I would trade up, get a quicker car with more power and a turbo is a must! Use the power to weight ratio to give you a good idea of performance and you'll get a good idea of your economy too, just make sure it's still a light car as weight is your biggest enemy. You will have slightly higher fuel costs perhaps, but you'll also have way more fun too!
I have done the powerful car and loads of fun but unfortunately, now that I am now surviving on a state pension and small private pension, I have had to cut my cloth accordingly. I bought the newest car I could afford and had to opt for the 1.2 litre over the 1.4 litre because of the tax advantage.
The Jazz is actually geared fairly highly. At 50 mph it is only pulling about 2100 rpm. At no time do I ever have to exceed 3000 rpm, well short of the 6000 rpm red line.
I've just got to make the best of what I've got.
It is certainly more fuel efficient than the Volvo S40 2 litre automatic that it replaced.
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Old 07-30-2017, 07:28 AM   #8
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Quote:
Originally Posted by R.I.D.E. View Post
If they had ever brought your Honda into the USA, I WOULD OWN ONE. The 1.2 idsi engine in your fit was tested and found to be very close to the efficiency of the original CIVIC VX lean burn engine, which was an amazing piece of automotive technology.
It is a wonderful little engine. Very flexible and quite torquey. With regards to speed and mpg I find that I can get great figures in a flat 20 mph zone. I sit in 4th at tick over and get 70+ mpg. I try my best to keep my highway speed down to below 50 mph.
These are my ScanGauge figures for yesterday's highway mileage.

Average mpg: 55.8 mpg
Max coolant temp: 91C
Distance travelled: 80.1 miles
Maximum revs: 3856 rpm
Max speed: 59 mph
Average speed: 32 mph

The 59 mph was a downhill section before a fairly steep incline. It gave me a bit if inertia and got me up behind a coach which wasn't hanging about.

The high revs were achieved on a very steep incline before one of the long descents.
As you can see my average speed was quite low, but that was due to a 3 mile stop start queue towards the Forth Road Bridge.
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Old 07-30-2017, 10:38 PM   #9
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Originally Posted by JockoT View Post
I have done the powerful car and loads of fun but unfortunately, now that I am now surviving on a state pension and small private pension, I have had to cut my cloth accordingly. I bought the newest car I could afford and had to opt for the 1.2 litre over the 1.4 litre because of the tax advantage.
The Jazz is actually geared fairly highly. At 50 mph it is only pulling about 2100 rpm. At no time do I ever have to exceed 3000 rpm, well short of the 6000 rpm red line.
I've just got to make the best of what I've got.
It is certainly more fuel efficient than the Volvo S40 2 litre automatic that it replaced.
I wasn't necessarily talking more expensive, just more powerful, think Ford Eco-boost, smaller engine than the Jazz 1.0L, but almost 100% more power, better economy, and just 20 tax too. It's 0-60 time is almost 4 seconds quicker too. PSA have some lovely 3 cylinder engines too, the 1.2L, same size as yours, has 130 BHP and double the torque. There doesn't have to be a compromise with todays tech, you can still have the efficiency, but the power and torque are there to help you overtake, keep up with traffic and push you up the inclines without having to work the engine harder.
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Old 07-30-2017, 11:19 PM   #10
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I looked longingly at the vehicles you mentioned, when looking to replace my previous car, but they were all well outside my price range. i just had to buy the best and cheapest to run IN MY PRICE RANGE. Buying a 1.2 Jazz, manual, with no air con was a huge come down after my 2 litre automatic Volvo S40, but it was a change necessitated by circumstance.
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