Before proceeding follow the link below;
http://universe-review.ca/I15-57-hyperbolic.jpg" onclick="window.open(this.href);return false;
As can be seen in the above graph it is evident that as the temperature rises (x-axis) the ambient temperature within the motor rises and therefore the efficiency of the motor is increased (y-axis)..
It is also seen however that the graphs all asymptote at a certain cut-off ambient temperature, this is because as the car engine reaches a certain temperature the pistons will no longer have time to fill up with fuel, so they will fire before the piston is full which will also lead to the motor contradicting itself to a point, because the 1st piston will fire at the same time the 4th one does, which will push one piston up and the other up as well, so they will be fighting against each other.
However there is no need to worry about this because unleaded and diesel do not ignite until approximately 150 degrees Celsius and 205 degrees Celsius, as shown in the graph.
Therefore it is evident that as the ambient fluctuating temperature increases, the efficiency and speed of the motor increase.
I hope this helps!!!

I have a 1991 model Sierra, it has been crashed, thrashed, bashed and rolled, but she will still get me up any damn hill I point her at! And that's why I call her Suzy.