Mpg And Temperature

[Ancient Nerd]

Thinking of some of the discussions about lower fuel consumption during the cold weather, I got hold of the monthly average temperatures for my bit of the country, and worked out the average monthly MPG over the last 2 years. On the chart, the red line represents temperature, and the blue line MPG.

The MPG covers 2 cars, a Gen II until July last year, and then a Gen III from September. The difference between the two cars isn't great, but there is a very obvious correlation between MPG and temperature of around 1 mpg per 2 degrees.

You might notice that the January mpg this year is somewhat better than expected. That is when I stuffed the grille with foam pipe insulation to cut down the airflow. February is also a bit better, because I took it off in mid-February, so half the month was good, the rest as normal. So next winter, the pipewrap goes back!

[DrCez]

That's quite a convincing correlation! I've noticed a big improvement in my MPG figures in the last week which I also attribute to increasing air temperature. In my case I'm travelling at low speed (average around 13 mph) and my impression is that the biggest change relates to use of the cabin air heater - certainly if I switch it off in slow traffic to discourage the engine from starting up it does seem to measureably improve my economy.

If grill blocking makes such a big difference, I wonder why Toyota didn't include something equivalent into the Gen 3 design, given all the other bells and whistles they added to eke out improved economy?

It will be a while before I have a full year's figures of my own but I am logging data in a spreadsheet which can be very helpful in identifying trends in fuel consumption as you have shown.

[wooski]

If grill blocking makes such a big difference, I wonder why Toyota didn't include something equivalent into the Gen 3 design, given all the other bells and whistles they added to eke out improved economy?

The Porsche 928 S4 introduced in 1987 had a movable flap to help warm the car up in it's nose. Porsche never got it work right and most dealers ended up disabling it (as some cars overheated with the flap not opening correctly). They dropped it on the later GTS model...

Some 23 years later you would think that Toyota could make this work reliably. I noticed in the cold weather that the car would warm up and the engine stay off in heavy traffic. As soon as you picked up speed in EV mode on came the engine again to warm itself up again. One of the problems here is that we don't get a temperature gauge....

[Fujisan]

Very interesting graphs, thank you.