Fuel Efficiency and the Yaris

[sbergman27]

Originally Posted by Boost Addicted

I also have to disagree with this lol. As you DO get zero mpg while warming up, you're getting worse fuel mileage driving it cold, especially in the winter... In the summer, not so much.

This very interesting topic is one which calls for a great deal of quantitative testing. It can't be discussed in coarse terms like "driving vs not driving" or "winter vs summer". Obviously, putting it in drive and letting the idle speed pull you toward the edge of the parking lot is going to get you better FE than just sitting there idling. On the other hand, turning the key and tooling out onto the 70 MPH Interstate is going to be worse than just sitting there at idle for a while. The truth lies in the minute details of the specific situation.

Intuitively, I would say that if it is practicable to drive very slowly and leisurely until the "Cool" light goes off (which happens at about 128F coolant temperature, BTW) then that is probably the best thing to do. I you must push the engine hard from your cold start position, then it may be best to warm it up a bit. This is not a question with a simple answer. And I'm not Aristotle. So I won't claim to have an answer based upon pure logic and reason.

We need some experimental data to sort this one out.

-Steve