90.6 MPG, my best effort so far

[Draigflag]

So I had the opportunity to go for a little drive on my own tonight. Not really had a chance to test the economy of my new car since I bought it in June, so thought I'd take this chance and see what I cold do with a little effort.

It was mainly rural roads, max speed limits were 60 MPH and minimum were 30 MPH, but I restrained my top speed to 56 MPH to save fuel when I could. On my short 30 mile trip, I guess around 20 % was down hill, so to take advantage of gravity I popped the car into neutral or dipped the clutch when I could. For the first 20 miles I was getting over 100 MPG as the gauge was stuck on 99.9 MPG, the max it will read. The big killer is acceleration, it's very difficult trying to reach a cruising speed without accelerating too harshly.

Even taking a few MPG's off the indicated reading which are nearly always optimistic, I'm still pretty pleased with the results. It by far exceeds the 78 MPG it got in the government tests, and is closer to the 88 MPG for the extra urban test, similar to the "highway" test for US cars. I would definitely struggle to keep this up over an entire tank however (like the mad person that got 97 MPG over 995 miles in a Golf TDI recently!) but it's good to experiment and see what you can do with a good bit of concentration!

[OliverGT]

Draigflag,

Well done.

Have to agree though, it's hard to translate good individual trips into a good full tank average.

I'm finding I'm still learning how to get the best out of my 206. I have no instant feedback which means I have to work tank by tank at the moment, which is difficult.

I'm looking at getting an MPGuino at some point in the future which should help me out.

Oliver.

[Draigflag]

Surely you must have some kind of indication of how many MPGs you get? I have the instant MPG reading which is pointlessly inaccurate, but the average MPG as shown is accurate within 5%

[OliverGT]

Draigflag,

Nope, no feedback, my 206 is from 2002, so 12 years old. Diesel Puegeots of that vintage don't comply with OBD2 standads either, I tried Torque and an ODB2 dongle with no joy.

So this is what I currently do:

1. Brim the tank
2. Note down mileage at each segment on the fuel guage, there are 8 segments, so each one should get me 100 odd miles, although some off them are better than others.
3. This gives a good idea during the tank on how I am doing compared to the previous tank.

I've only just started with this method and it seems to working, roughly! But at the moment, it is the best I can do.

I'm sure with feedback, I could do better than I currently am. The only option for me though is the MPGuino, which involves a lot of DIY wiring, so might take me a while to get it installed and running.

Oliver.

[Draigflag]

Ah I see. So are you tracking miles by the odometer then? At least fuelly will give you accurate results, I guess you just have to wait until every fuel up to find out your average MPGs.

[evoblade]

Draig, do you stop the motor when you put the car in neutral? That can be dangerous under some circumstances. I'm assuming you don't. If not then doesn't your car have to use fuel to spin the motor while in neutral. I'm not a hypermiler, but I always assumed even with the extra drag to spin motor, it is still better to coast in gear and not burn gas just to turn motor than the alternative (neutral).

[Draigflag]

Originally Posted by evoblade

Draig, do you stop the motor when you put the car in neutral? That can be dangerous under some circumstances. I'm assuming you don't. If not then doesn't your car have to use fuel to spin the motor while in neutral. I'm not a hypermiler, but I always assumed even with the extra drag to spin motor, it is still better to coast in gear and not burn gas just to turn motor than the alternative (neutral).

No I don't stop the engine, it's impossible to turn the engine off above 10 MPH in my car anyway (it has push button start with no key/ignition) I also consider this extreme and dangerous, as not only do your brakes not work properly, but all the electronics including lights, steering etc etc.

I've experimented with neutral, and in gear coasting. You're right to say the fuel cuts out when in gear coasting, however you still experience engine braking whilst in gear. I've found it more efficient on large descents to pop it in neutral, and the car will pick up speed quicker and go further without the engine braking. It's also the only time I really speed, I like to make the most of gravity!

[OliverGT]

It's generally accepted that the order of efficiency goes like this:

1. Coasting Engine off (I don't do this!)
2. Coasting in Neutral - engine uses fuel to idle.
3. Leave in gear, but no throttle - in some cars engine uses no fuel (fuel cut off)

Although you are not using any fuel with 3, because of engine braking you won't be able to roll as far, this generally makes it less efficient than 2, which uses a small amount of fuel, but allows you to roll further.

I would use both 2 and 3 depending on the circumstances, for example on my commute, I have a right turn at the bottom of a short hill, there is no way you would make this turn, no matter how slow you were going coasting in Neutral from the top, so I use option 3 at this point on my commute.

Similarly, if I get the timing wrong on some of the lights I will use option 3 over option 2.

If you have a instantaneous MPG guage, you can see if you get fuel cut off, and how low the RPM's can go before it cuts back in. I can't but still use option 3 when required, just in case

My understanding as well, but I am open to correction on this one, is that Diesel engines use very little fuel at idle, compared to petrol engines. I have an example for a petrol engine - 0.6L per Hour for a 1.2 Skoda Fabia. I can't do the sums at the moment, but I think this works out at about 300-400 mpg if you are coasting in Neutral at 30mph.

[Charon]

I was just reading through the manual for Commercial Drivers, since I have to renew my bus license this fall. In that manual it describes "unsafe coasting" as coasting more than the length of your vehicle, either in Neutral or with the clutch disengaged. Doing so will cause an automatic fail on the driving test.

[Draigflag]

I have to retake my driving test in 2057, so im not going to worry about that now...

and I don't live in the US thankfully, and I don't drive a bus either...