Fuel Efficiency and the Yaris

[Boost Addicted]

'10) and never idle it to warm it up. The Yaris offers a low coolant indicator light in the dash panel that let's you know when it is running in its least fuel efficient state. As for idling to warm it up, remember that you're getting exactly ZERO MPG while idling.''


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.

But in the winter, metal shrinks even more with the colder weather, and your tolerances are loose (eg. piston rings, oil pump gears, valvetrain) making operation sloppy, inefficient, and less resistance to wear. In addition, the coolant temp sensor will dump a bunch of extra fuel until the engine is at its operating temperature... So even though you're running rich at idle to warm it up, you're still using more fuel when driving it cold...

Ofcourse, when you measure lost MPG's when letting it warm up at idle, vs driving it right off the bat, numbers will be lower... But if you calculate volume of fuel used to warm the vehicle at idle vs. volume of fuel used to warm it driving when its cold, idle will get better mileage every time.

In summer weather its really not necessary.. But regardless of ambient temperature, you shouldn't put the car in gear untill 10 seconds after ignition to allow for oil to properly lubricate all parts of your engine

Just my .02 :)

[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

[Boost Addicted]

Honestly I don't feel the truth lies in minute details of the situation... But none the less, the huge factor of increased engine wear is at play. And mileage doesn't matter too much when you have worn piston rings at 150K.

And this isn't based on ''pure logic and reason'', its based on fuel mileage calculation.

[sbergman27]

Originally Posted by Boost Addicted

Honestly I don't feel the truth lies in minute details of the situation... But none the less, the huge factor of increased engine wear is at play.

That is a different, but valid, vector, which I was not addressing. But I would say that it actually *increases* the complexity of the question. I would agree that including that metric would shift things a bit toward delaying, or slowing down the allowed driving speed.

Consider that you are going to get more miles out of the engine if you start it and let it idle in drive, at whatever speed that gets you, and if conditions allow, than if you just sit there getting 0 miles per revolution out of it.

Actual data *is* needed to map this landscape.

-Steve

[Boost Addicted]

Meh ::shrugs::, I'll drive how I drive and you guys can drive how you drive lol, I was just throwing in my .02

All I'm saying is, with the way I drive as specified above (this is for the Jetta, my girlfriend has the Yaris) I get 34mpg combined city highway... And I have about 275wtq. I'm not bragging about numbers, I think the Yaris is a very solid built car, everything feels tight, its comfortable, and its practical... I'm just saying that if its possible for a larger displacement engine with much more power to get as much fuel mileage as it does, you Yaris owners could benefit from the same techniques and practices I use to get the full potential out of your car.

[Loren]

Originally Posted by Boost Addicted

All I'm saying is, with the way I drive as specified above (this is for the Jetta, my girlfriend has the Yaris) I get 34mpg combined city highway.

34mpg is good for your car, I'm not going to say it isn't. But...

34mpg is only 17% more than the EPA rating of 29 hwy for your Jetta.

Who do we trust for advice on how to most efficiently drive a Yaris? The guy who drives a Jetta and only beats EPA by 17%... or the guys who drive Yarii, and regularly beat EPA by over 30%?

I took the advice of the guys getting over 30% better than EPA (that's 47+mpg), learned and practiced the techniques, and now I *am* one of those guys.