Ave Mpg Display

[Hybrid-Harry]

The long term MPG checks on my Yaris Hybrid carried out over 1000 miles from full tank to full tank worked out as an average of 63.4 MPG, whereas my display on the dash shows 62.8 over the same period.

I have never relied on the dash readouts, as all my other cars always stated about 5-10 MPG over the actual MPG. But it seems my Yaris is actually very accurate, perhaps the manufacturers have been instructed to make the processing more accurate.

[alan333]

Of our 5 current and previous Toyota's... Four read around 5% high and one was bang on.

[YarisHybrid2016]

How do you fill up? The manual says to NOT "top off" the tank as it "could damage fuel system components", but two things: the first is I always "top off" the tank, and not had any issues with any vehicle as far as I'm aware. Second, it is the only way to KNOW the tank is full, without dipping it.

I don't trust the auto cutoff of pumps, not least due to the anti-siphon filler neck.

[Hybrid-Harry]

How do you fill up? The manual says to NOT "top off" the tank as it "could damage fuel system components", but two things: the first is I always "top off" the tank, and not had any issues with any vehicle as far as I'm aware. Second, it is the only way to KNOW the tank is full, without dipping it.

I don't trust the auto cutoff of pumps, not least due to the anti-siphon filler neck.

I always use the same pump at my local garage, I wait for the first nozzle trip, then go again till the next one, then stop. I never force more in.

I find filling up with petrol is more accurate than diesel because diesel frothes and causes the nozzle to trip easier.

[YarisHybrid2016]

Interesting. When I wrote my other post I was wondering if you did that (used the same pump each time).

Related note: approximately how much fuel is remaining when the low level light comes on?

[Lesolee]

Does it really matter? If you put in a bit less this time then you may need a bit more next time. I just let it auto-shut off and that's it. I don't care if it is the same pump or not. Over many tanks it will average out.

What I do find is that getting stuck in traffic increases my mpg, the car being more fuel efficient at lower speed.

[YarisHybrid2016]

Why the hostile tone? If we're being scientific about it, then yes, repeatability of the results matters.

[Sagitar]

I'm not sure what it is that you are trying to repeat. In dealing with specific consumption for a single tank there are many variables other than the ones that have been mentioned. Taking an average over many fills tends to even out the effect of all these variables.

In trying to compare two vehicles, I would find the average over (say) a couple of years, far more meaningful than the figures for a single tank full.

[Lesolee]

Ball park estimates:

8cm fuel filler (estimated not measured)

8cm estimated uncertainty in fuel level using auto-shut off on any pump (at the same petrol station)

pi*4*4*8 = 402cm^3

Typical tank fill 35 litres.

±100 * 0.201 / 35 = ±0.6%

typical mpg 62mpg; uncertainty is ±0.4mpg

Does it really matter?

My figures on tank to tank mpg since Jan this year (when I got the car)

48mpg

52mpg

54mpg

58mpg

59mpg

60mpg

62mpg

There are two factors which I consider dominant (without "proof").

1) The weather has been warming up and I don't think the car likes being cold, especially on short journeys.

2) I am getting better at driving the car economically.

The mpg values are quite low because of the 3.5 mile trips to work. On a recent trip out and back to the same location through the Oxfordshire countryside (over an hour or so) the mpg readout was 81mpg!

The average mpg reported by the onboard system reads about 4mpg high compared to my manually calculated value, showing that my filling/measurement method is pretty repeatable.

I find that driving in rain really hammers the mpg. The (measured) power consumption of wipers and headlights doesn't account for it. I imagine that hitting rain is aerodynamically worse in drag terms than hitting stationary air.

[alan333]

I always thought reduced fuel consumption in rain was due to increased road resistance by the water.

[MEP's Yaris GS]

I personally always 'brim' to full, to the point I can see the fuel in the neck, never had any issues myself with doing this in any of my cars, including our current Yaris and my PiP.

[Lesolee]

I always thought reduced fuel consumption in rain was due to increased road resistance by the water.

Interesting. Probably quite difficult to test the difference between the two loss mechanisms (for enthusiasts without access to dedicated test tracks) since if it is not raining the road won't stay wet for very long. Something to put into the mix for future Torque Pro logging sessions!

[kithmo]

Ball park estimates:

8cm fuel filler (estimated not measured)

8cm estimated uncertainty in fuel level using auto-shut off on any pump (at the same petrol station)

pi*4*4*8 = 402cm^3

Typical tank fill 35 litres.

±100 * 0.201 / 35 = ±0.6%

typical mpg 62mpg; uncertainty is ±0.4mpg

Does it really matter?

My figures on tank to tank mpg since Jan this year (when I got the car)

48mpg

52mpg

54mpg

58mpg

59mpg

60mpg

62mpg

There are two factors which I consider dominant (without "proof").

1) The weather has been warming up and I don't think the car likes being cold, especially on short journeys.

2) I am getting better at driving the car economically.

The mpg values are quite low because of the 3.5 mile trips to work. On a recent trip out and back to the same location through the Oxfordshire countryside (over an hour or so) the mpg readout was 81mpg!

The average mpg reported by the onboard system reads about 4mpg high compared to my manually calculated value, showing that my filling/measurement method is pretty repeatable.

I find that driving in rain really hammers the mpg. The (measured) power consumption of wipers and headlights doesn't account for it. I imagine that hitting rain is aerodynamically worse in drag terms than hitting stationary air.

and don't forget the fact that the engine is loosening as it gets run in.

[Lesolee]

and don't forget the fact that the engine is loosening as it gets run in.

True, but not relevant. The car was 1 year old with 5000 miles on it when I bought it

[YarisHybrid2016]

Nice analysis of the filler neck, and interesting fuel economy results!

[MEP's Yaris GS]

and don't forget the fact that the engine is loosening as it gets run in.

True, but not relevant. The car was 1 year old with 5000 miles on it when I bought it

Still loosening up then, most cars don't reach their peek until 30-50k+ miles from experience, this is even longer in a hybrid I'd have thought with its lower usage cycles of the engine.

[Lesolee]

Still loosening up then, most cars don't reach their peak until 30-50k+ miles from experience, this is even longer in a hybrid I'd have thought with its lower usage cycles of the engine.

I can’t say I have ever noticed that or heard it mentioned before.

I checked my old Corolla (2000 vintage – 15 year old data) and it has running in for the first 1200 miles. My Auris handbook has the same 1200 mile figure. Probably fairly generic data.

I do remember the old advice to warm up an engine before starting off and note that even 15 years ago that was changed to a “warm up” period of 10 seconds in the 2000 Corolla handbook (page 177).

As we head towards winter I will be able to measure my mpg performance in colder weather and that will tell me if it is my driving, the weather, or any sort of running in effect that is dominant.

[johalareewi]

There does seem to be a running in period for toyota hybrids.

I guess the various onboard computers have to learn and adapt to what works best.

As does the driver.

[YarisHybrid2016]

When I first drove mine, it clearly didn't want to go anywhere. After 200 miles, it still seems slow when cold, but is already starting to feel nippier in slow traffic.

I'm still apprehensive of doing a long motorway drive with it. I do some dual carriage way for maybe 15 minutes, but not sure whether running 300 miles at mostly motorway speed is a good idea with such low milage? I'm curious as to why they say not to drive at a constant speed whilst running in. I'm currently doing a mix of "A" road/town driving, to use everything gently but frequently.

[MEP's Yaris GS]

Still loosening up then, most cars don't reach their peak until 30-50k+ miles from experience, this is even longer in a hybrid I'd have thought with its lower usage cycles of the engine.

I cant say I have ever noticed that or heard it mentioned before.

I checked my old Corolla (2000 vintage 15 year old data) and it has running in for the first 1200 miles. My Auris handbook has the same 1200 mile figure. Probably fairly generic data.

I do remember the old advice to warm up an engine before starting off and note that even 15 years ago that was changed to a warm up period of 10 seconds in the 2000 Corolla handbook (page 177).

As we head towards winter I will be able to measure my mpg performance in colder weather and that will tell me if it is my driving, the weather, or any sort of running in effect that is dominant.

Running / bedding in and loosening up / returning better performance with use are two different things. Don't confuse the two. Some DERV users report their cars doing better MPG with 150k on the clock over 50k - both of which are very much 'run in'.

[MEP's Yaris GS]

When I first drove mine, it clearly didn't want to go anywhere. After 200 miles, it still seems slow when cold, but is already starting to feel nippier in slow traffic.

I'm still apprehensive of doing a long motorway drive with it. I do some dual carriage way for maybe 15 minutes, but not sure whether running 300 miles at mostly motorway speed is a good idea with such low milage? I'm curious as to why they say not to drive at a constant speed whilst running in. I'm currently doing a mix of "A" road/town driving, to use everything gently but frequently.

Just drive it and worry a little less. Most fleet or company cars are driven like they're stolen from day one without issue.

[YarisHybrid2016]

Just drive it and worry a little less. Most fleet or company cars are driven like they're stolen from day one without issue.

That's true, and something I do consider. I'm just intrigued that considering modern manufacturing, they get specific regarding the running-in period. Earlier today I did a maximum acceleration onto a busy road, so I'm not being paranoid or anything (the car was not cold which is important).

More harm is done at cold start-up than any other time. This is why diesels are a bad choice for short journeys. Pratt and Whitney ran a PT6 turbine for over 5 years continuously (it was used as a pump). When they did a tear-down of it, it was like new.

[Hybrid-Harry]

Hot or cold start it makes no difference as Toyota has used Nikasil coating on their engines for several years now, so there is no initial service, and no need to run the engine in.

Nikasil is a coating applied to the cylinder bores that prevents piston ring wear. It also eliminates the need for honing if the piston rings are replaced.

I have in fact had a bored out block re-coated when it threw a rod on Brands Hatch during a race.

[Lesolee]

Hot or cold start it makes no difference as Toyota has used Nikasil coating on their engines for several years now, so there is no initial service, and no need to run the engine in.

I googled it and couldn't find any confirmation of the use of Nikasil on Toyotas. Can you provide a relevant link?

[YarisHybrid2016]

I can certainly confirm the "no initial service" part. First service for me will be in a year's time as I won't be doing sufficient milage for it to be any sooner (otherwise I think the first service would be at 20,000 miles).

That compares with previous cars where I had to have a "first service" at around 6000 miles, primarily to change the oil.