Battery Vehicle Society

Hi folks.

I've been testing a well-known mod in the last week on Velma to see if it makes any difference to fuel economy.

The mod involves attaching a section of foam pipe insulation to the top part of the Prius grille.



It seems after half a tank that the car is reporting a total mileage so far of 315 miles or so at an estimated 59.7 mpg. Until yesterday it was at 60.4!

This is much higher than anything I've experienced over a tank. Yes, I've got 62.4 for motorway driving on a hot day, but it's certainly not stayed that way!

Anyone else played with this mod? The foam cost 50p from B&Q.

Nikki, I did something similar during the winter months but I wedged a piece of packing foam in front of the radiator but behind the grille. I had to unscrew a plastic cover from the top of the radiator area for access.

I felt that it made a positive difference to economy when the weather was cold but I removed it in the spring as I felt that without any temp gauge in the car I would have not indication that the temp was getting out of line until I got a major warning. I guess you will be able to monitor this with your cann bus scanner, so I would be interested to know if you do see any dangerously high tempratures.

MT

PS I've got 67MPG over 450 miles on my current tank but I have had some very favourable conditions.

Hi Mark,

At the moment I'm driving very short distances, so the engine really isn't getting a chance to overheat.

However, I'd be interested to know how you're getting such high figures. What is your average drive? How do you get that wonderfully high figure? Are your tyres higher pressure than recommended?

I fear that if you come on the London-Brighton you'll whip both Kate and myself into embarrassment. Our average MPG runs between 56-58 for Kate and 58-61 for me.

Teach us, oh Yoda of the Prius!

The EMF is strong with this one, gentle with the gas pedal you must be.

Yes Nikki I do run the tyre pressures a bit high, the label inside the drivers door has a graphic showing the correct settings for unladen or for loaded/ high speed use. I take the figures for loaded / high speed and add 2 psi so I have 40 psi at the front and 38 psi at the back. I am not recommending that anyone else does this, it is what I do. It makes for a firm ride but it's not uncomfortable.

My regular commute is just over 22 miles each way crossing the South Downs, this (I find) is just far enough to recoup the dip in MPG when I first start off, travelling further starts to produce real gains. I try not to do short journeys (below 5 miles) but sometimes it's unavoidable.
I keep my speed down and try to never touch the brakes (you will appreciate this as an EV driver) I am happy to do 60mph on dual carriage ways and Mways. Matching my speed with the HGVs is no hardship. I also use the cruise control constantly. In a built up area I use the cruise and set it for 31 or 32 mph. (the digital speedo is optimistic but that’s a very long story) 29 or 30 causes queues to form, I might stretch the speed limit a bit if the gradient is favourable but that is usually to give me some momentum to get up the other side. Under warm dry conditions on my regular route I would get 61 to 64 mpg.

My current figures are a bit better because (you won’t believe this) I had a few runs around the M25 last week!! The variable speed limit (50 is better than 60) from the A24 to the M3 is a gift and the road is pretty flat in that area.

When I fill up next (probably tomorrow) I will calculate my real MPG (the computer is nearly always optimistic) but I would expect a true value of about 64 -65 mpg.

I am planning to do the L to B but I will meet you at Hand Cross so prepare for a challenge.

I have all my mileage data in a spread sheet but I need evidence that your anorak has at least as many poppers and zips as mine before I can be persuaded to share it!!


MarkTime

Mark,

I have oodles of poppers and zippers. Mainly in the form of the CanView

I've upped my tyres to 40/38 too, so it's going to be interesting to see what we can come up with. I too use cruise control where I can, though in Bristol the traffic is so stop/start it's tough. That's why I'm doing the PHEV mod!



I think you get the advantage on me when it comes to trip length. I don't really get good fuel economy on my trips into Bristol unless I take the motorway. Trips less than 8 miles seem to zap any sense of good mpg...

Today the mileage dropped significantly (thanks, rain) to 58.8 mpg. I have just crossed over into the last half tank as indicated on the display. 350 miles

So you're only coming half way eh? Don't forget to fill out the entry form though!

Nikki.

Is it possible to post a spreadsheet on this forum?

MT

Here's a teaser.



The Pink line shows the MPG calculated after each refill (miles travelled over gallons to refill the tank). MPG on the left axis.
Beginners mileage on the left during the winter of 2006 improving during April and May last year when the weather was warm and dry, last summer was poor but it did not get worse during the winter. Average over the whole period is about 58 MPG. MPG calculated this way is nearly always less than data from the on board computer.

The Blue line is a figure for pence per mile (right axis) (I have an exe prog that does the maths for me). Best ever 6 pence/ mile, sadly I can’t get below 8 pence/ mile at the current rate.

The yellow line is a bit embarrassing; it's the rate at which my employer reimburses me (all drivers with petrol engines up to 2.0l). So the area between the blue and yellow lines represents profit!!

MT

Did you mean that Nikki? or was it "I ALSO use ..."? I can't see where marktime says he does this.

I have only used cruise control on hire cars, but I usually switch it off as I feel it uses MORE gas than I would on my own.

Coming up to a hill, I can see ahead to decide wether I can let the speed bleed off, to be regained on the downhill, and keep the throttle position fixed. Cruise control can only advance the throttle to keep the speed fixed, thereby using more gas.

I have no data to back this up, it is just my feeling.

The only advantage I can see is long motorway cruising, where I might allow the speed to creep up, but the cruise-control has more restraint ;-)

I am interested in your experiments.

Tim you are right that cruise control cannot see hills so cannot predict the need to build up speed or to ease off but I do believe that it can be used as an aid to economy on the Prius.

It can maintain a steady speed on a level road very well with minimum power input and will often do it with just a bit of electric nudge.

When I use it I do not always keep to a constant speed but I use the inputs to the cruise control as an accelerator, up 2 or 3 mph here (or enough to overtake if I plan it well) down 1 or 2 there. The cruise does not give much / any braking force but if you keep your distance from the car in front and watch what is happening ahead you can loose 1 or 2 mph quite safely without touching the brakes.

When I first got my Prius I did not believe that the cruise could do a better job than I could but I was not happy with the mpg I was getting so started to use the cruise and it got better.
The technique is not very easy to describe but I hope you get the gist.

MarkTime

Time for a caveat:

My comments about tyre pressures and cruise control etc are all based on having considered any saftey implications, I am not suggesting that anyone else should try to copy them unless the consider they saftey factors for themselves.

i.e Setting the cruise control is not an oportunity to put the kettle on and make a cup of tea, driving still requires the drivers full attention.

Saftey is more important than economy.

Just wanted to make that clear.

thanks mark