variablevalve

Question 1.
Driving with your A/C on lowers your fuel efficiency because it's belt driven (Correct?) If so, does the temperature you set the A/C affect the fuel efficiency?

my guess would be NO because the temperature control only changes the amount of air running through the A/C vs amount of air from outside (correct?) so therefore it shouldn't have any affect on the amount of effort put on the engine.

So therefore, because the fan is electrical, if you're going to use the A/C you might as well set it at the coldest setting and turn the fan up all the way?

-

Question 2.
Following closely behind another car will reduce the amount of effort on the car's engine therefore increasing fuel efficiency (correct?). If this is so, then how closely do you need to follow. NASCAR drivers are within inches of each other for this reason, and is this the only effective distance?

I ask because when driving long distances I often tail behind large trucks, SUVs, etc because I hope that by being in their wake I can increase my fuel efficiency. I usually follow close, but not tailgating close (20-25 feet).

Is it possible that if I follow closely but not close enough that the air comming down off the car in front of me (which is traveling downward) can actually push down on the front of my car and decrease my fuel efficiency?


thanks




Modified by variablevalve at 8:22 PM 5/30/2006

Runnerdown

Ok, anytime the engine has to do more work, it uses more fuel. A/C on is running the pump/compressor obviously and puts a load on the engine. the colder you tell it to go is making the system work more, and also turning the fan on high increases electrical draw and makes the alternator work harder. its a lose, lose situation. Following close behind another vehicle puts less aerodynamic resistance against making the engine not work as hard to maintain speed.

StorminMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by variablevalve &raquo;</TD></TR><TR><TD CLASS="quote">Question 1.
Driving with your A/C on lowers your fuel efficiency because it's belt driven (Correct?) If so, does the temperature you set the A/C affect the fuel efficiency?

my guess would be NO because the temperature control only changes the amount of air running through the A/C vs amount of air from outside (correct?) so therefore it shouldn't have any affect on the amount of effort put on the engine.

So therefore, because the fan is electrical, if you're going to use the A/C you might as well set it at the coldest setting and turn the fan up all the way?

-

Question 2.
Following closely behind another car will reduce the amount of effort on the car's engine therefore increasing fuel efficiency (correct?). If this is so, then how closely do you need to follow. NASCAR drivers are within inches of each other for this reason, and is this the only effective distance?

I ask because when driving long distances I often tail behind large trucks, SUVs, etc because I hope that by being in their wake I can increase my fuel efficiency. I usually follow close, but not tailgating close (20-25 feet).

Is it possible that if I follow closely but not close enough that the air comming down off the car in front of me (which is traveling downward) can actually push down on the front of my car and decrease my fuel efficiency?


thanks </TD></TR></TABLE>

1. Increasing the temperature setting does NOT increase either power or fuel economy. The reason? It doesn't affect A/C operation in any way, shape, or form. Contrary to popular belief, running the A/C at a higher temperature does NOT make the compressor cycle on less frequently. Rather, turning up the temperature simply uses the heater to increase the temperature of the air coming out of the A/C. So the A/C is cycling on just as much as with maximum cold. And the heat, as you know, comes from the coolant. So the overall fuel consumption is unchanged.

As for the fan, the amount of power it uses is negligible. But on a side note, I should mention that, at high speeds, forgoing the A/C and rolling down the windows INCREASES fuel consumption due to increased drag. And before you bring up the episode of Mythbusters, keep in mind that (1) they used trucks, which are not very aerodynamic in the first place, and (2) speeds were limited to 45MPH.

2. Drafting other vehicles can indeed increase fuel economy. I do not know, however, how closely you should follow OR how great the savings will be. But they are likely not enough to justify having to tail someone (at least not enough for me).

variablevalve

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">Contrary to popular belief, running the A/C at a higher temperature does NOT make the compressor cycle on less frequently. Rather, turning up the temperature simply uses the heater to increase the temperature of the air coming out of the A/C. So the A/C is cycling on just as much as with maximum cold. And the heat, as you know, comes from the coolant. So the overall fuel consumption is unchanged.
</TD></TR></TABLE>

Thanks, that's what i thought.

I would still like a more definite answer to question 2 though, anyone?

thesmogman

I would say to #2 is you lose the draft after two car length's on a car. Depending on the size of the car/truck maybe four.

I did my testing with a car that had no clutch. I had to draft just to get it up hills on the freeway.

erikiksaz1

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by variablevalve &raquo;</TD></TR><TR><TD CLASS="quote">Thanks, that's what i thought.

I would still like a more definite answer to question 2 though, anyone?</TD></TR></TABLE>

I can't remember where I read this, but they tested the draft theory, and it works. But would it be safe and reasonable, no. They said you'd have to be pretty close to the back of the truck for it to work.