idiling vs. driving

jnperin · August 27, 2005

While putting a few back the other night we got into a discussion on which used more gas to get an engine from resting temp. to normal operating temp.Idiling or driving at 65mph. I believe it uses the same amount but the air passing through the radiator and engine compartment at 65mph would mean idiling would use less fuel. If anyone could shed some light into this it would be much appreciated.

Jim

facn8me · August 28, 2005

Well if you going by MILES per gallon. Idling would be worse be cause your getting zero miles for your gas.

Edit to add this: My opinion is to start your vehicle. Let the engine stabilize at idle(even fast idle) The put in gear and drive sensibly to operating temp. Uses the least amount of gas and easist on vehicle.

Jerther · August 29, 2005

Here's my theory

At idle speed, the engine uses just enough gaz and air to keep it running without going too fast. There's almost no resistance to the engine, so without a control on the air/gas the engine would reach high rpms and.. explode?????

However, when the vehicle is moving. More resistance to the engine apears: mechanical parts, friction due to tires and wind. More resistance means more fuel to keep the engine running at a steady rpm.

Just think of yourself on a bicycle. Is it easier to stand still (your body still uses some energy to keep itself alive) or to run at 20-25 km/h? If the conditions are good (no hills and things like that) you would see no big difference, but to keep yourself going at 20-25, you have to work against the wind and the friction of the tires on the ground.

And let's not consider that you have no fan to cool yourself down

facn8me · August 31, 2005

But your burning gas and not going anywhere.

This is the theroy on the hybrids. When you stop the fossil fuel burner stops and it's using zero fuel. Consequentially using electricity to move the vehicle and start the engine keeps fuel usage down. When cruising the gas engine only runs the vehicle due to cruise rpm generally being the most fuel efficent.

So anytime the vehicle is not moving and the engine is running it is a waste of energy.

Jerther · August 31, 2005

But your burning gas and not going anywhere.

This is the theroy on the hybrids. When you stop the fossil fuel burner stops and it's using zero fuel. Consequentially using electricity to move the vehicle and start the engine keeps fuel usage down. When cruising the gas engine only runs the vehicle due to cruise rpm generally being the most fuel efficent.

So anytime the vehicle is not moving and the engine is running it is a waste of energy.

<{POST_SNAPBACK}>

I agree. So is someone who doesn't do anything useful off his/her time

Skipponator · August 31, 2005

Well here is my theory:

For fuel usage I believe idling uses less, why do I think this?

2 Winters ago I left my Wife's Intrepid running in the Winter for just over 12 hours (forgot I started it after coming home from the weekend), woke up in the morning to find the car running, it had used 1/4 tank of fuel. Now is it possible to use 1/4 or less of fuel driving 12 hours, no matter what speed in a normal vehicle? I don't think so.

Now for emissions, I hear idling is the worst......

facn8me · August 31, 2005

Well here is my theory:
For fuel usage I believe idling uses less, why do I think this?

2 Winters ago I left my Wife's Intrepid running in the Winter for just over 12 hours (forgot I started it after coming home from the weekend), woke up in the morning to find the car running, it had used 1/4 tank of fuel. Now is it possible to use 1/4 or less of fuel driving 12 hours, no matter what speed in a normal vehicle? I don't think so.

Now for emissions, I hear idling is the worst......

<{POST_SNAPBACK}>

How many miles did you get out of idleing for 12 hrs? And does it differ from 1/4 tank of driving? I will geusstimate your intrepid get's 20mpg and holds 16 gal of gas. Using this equation 1/4 tank of gas is 4 gal. Now driving you will see 80 miles of driving on 4 gal's of gas. Sitting in your drive way idleing you get what? Zero miles to the gallon. So if we times Zero times 4 gal we come up with zero miles for 4 gal's of gas. So zero miles or 80 miles?

Skipponator · August 31, 2005

We're not talking MPG, aren't we talking about fuel consumption? Engine is running, which mode is burning more? Moving or idle?

facn8me · August 31, 2005

My point is why is it running if it aint movin. It's consuming fuel for no reason at all. How is that better?

redvett · August 31, 2005

With gas on it way to $5 a gallon soon i dont think anyone wants to idle or even drive. Because of Katrina we are in for a bad time for a while.

toneman · August 31, 2005

We're not talking MPG, aren't we talking about fuel consumption? Engine is running, which mode is burning more? Moving or idle?

<{POST_SNAPBACK}>

Exactly! Why don't some of you folks go back and read the original post a bit more carefully?

All the original poster was asking for was which method would burn more gas in order for the truck to reach operating temperature--let the truck idle until it does, or drive it around for a bit? I mean, it's not as if he was asking how many miles does it take for the engine to warm up...

facn8me · September 1, 2005

We're not talking MPG, aren't we talking about fuel consumption? Engine is running, which mode is burning more? Moving or idle?

<{POST_SNAPBACK}>

Exactly! Why don't some of you folks go back and read the original post a bit more carefully?

All the original poster was asking for was which method would burn more gas in order for the truck to reach operating temperature--let the truck idle until it does, or drive it around for a bit? I mean, it's not as if he was asking how many miles does it take for the engine to warm up...

<{POST_SNAPBACK}>

I understand what he asked. I stupidly tried to explain my opinion. Just having a car running does use less gas than driving it. Since the work produced by the idleing engine is nada. I figured actually getting use out of the fuel your burning would be more efficent. I have been corrected.

Skipponator · September 1, 2005

However, you want to let it idle to run temp (basically Winter months) so everything heats up evenly, otherwise stuff expands faster, liquids thin out slower, etcc..., and you can have excessive wear on engine internals.

jnperin · September 1, 2005

However, you want to let it idle to run temp (basically Winter months) so everything heats up evenly, otherwise stuff expands faster, liquids thin out slower, etcc..., and you can have excessive wear on engine internals.

<{POST_SNAPBACK}>

This discussion is sounding alot like the discussion my friends and I had before I bought up this topic on this thread! anyways thanks for all of your opinions. I still believe you burn less at an idle than running at 65mph. Maybe I should submit this question to Mythbusters.

Jim

Wingnut · September 1, 2005

Simple test...Start your truck, and try to go 65mph with the throttle body in the same position as it is at idle (pretty much closed). If that were possible, it would be a neat trick Not to mention that if you could figure out how to have a truck power itself to 65mph with the engine idled, you'd be a very rich man.

So do this even simpler experiment: Have a friend sit in the cab with the truck running, and you get under the hood and remove the intake pipe so you can watch the throttle body open up from idle as he presses the accelerator until RPMs reach 1600-1700 (leave it in park there genius ). The throttle body fluke/flap/butterfly/whatever will be much more open at 1600 rpm than it will ever be at idle.

The wider the throttle body is open, the more air is sucked in to the motor...And the only way more air works, is with more fuel.

This tells me without doubt that it burns more fuel when going 65 (1600 or so RPMs), and this is without factoring in what it takes to rotate the drivetrain or move the truck through the air.

Idling = less gas...Period.

But I never took engineering, and I didn't stay at a Holiday Inn Express last night, so I could be way off.