I have read somewhere else about closing all windows while driving on a highway. I think this may reduce wind resistance at high speed. However, some fuel economy advice givers say the difference this measure can make is small. So it is up to you to consider whether to add it to your list.
My scan gage shows that window open is less load than running AC. Modern cars have abominable ventilation systems, bringing in air that is above outside air temp, forcing you to either run AC or keep a window open in hot weather.
Here, we like to go deeper into those ideas. I can offer some additional insight into some of them.
That is a valid strategy. However, the opposite strategy can also work very well. I have had great success with opening the throttle a lot. I step on the throttle pedal hard whenever I can. I know that it has produced very good results for me, but to explain it I only have theories. Two of those theories are:
- Reduced pumping loss. For a certain amount of work the engine has to do, it has to move a certain amount of air. Whether it moves that air easily past an open throttle or with more difficulty past a closed throttle can make a difference in efficiency.
- Using the engine in its most efficient range. It can be measured and displayed with a BSFC chart (search for information on that). Most engines produce work most efficiently when heavily loaded. This may be because friction and reciprocating loss at a certain RPM is approximately the same whether it's producing a little work or a lot.
It doesn't work for everybody, but it works great for me.
This is called DFCO (Deceleration Fuel Cut Off). As long as you need to reduce your speed, it's very effective. It helps to know the exact conditions in which your engine will DFCO, though; the programming can be very picky about when it will DFCO and when it won't. It is not as common as most people think.
We call it a "block heater".
That can vary based on your driving. If you are driving in stop-and-go traffic, such as in a traffic jam or in a city, that's very true; you should open your windows instead. If you are driving steady at high speed (80kph and more), it may be more efficient to close the windows and use AC instead, because of the aerodynamic drag caused by the open windows.
Note that the BSFC is far higher at near full throttle than at near idle where we cruise most of the time. The reason heavy throttle application followed by coasting (pulse and glide) works is that the engine efficiency is so much greater at full throttle.......Now if we could simply shut off the engine during the glide portion somehow, it would really work well. With my Subaru, I could, as it will restart by letting out the clutch, but steering is harder. Why do we need power steering on these small cars??
#1 SLOW DOWN
#2 Don't Buy Ethanol fuel if you can help it.
Testing for ethanol is fairly simple. A measured amount of gas is mixed with a measured amount of water, if the total is less than the amounts of the two, then there is alcohol in the fuel. Ethanol not only cuts down mileage for that tank, but seems to carry forward for some time, suggesting that the slightest amount of ethanol has a significantly detrimental effect on engine efficiency. Little wonder that the gas companies do not seem to be working to kill the ethanol industry, even though it's an absurdly wasteful one. Net energy going into producing ethanol if you take everything into account, exceeds the energy available in the fuel........ It's win win for the oil companies!!
My DD is a 2000 Dodge Dakota and I wanted to share some things I've used succesfully and some things I found interesting. Most apply specifically to trucks, but many may be used on a car as well.
1) SCT tune- I had my computer dyno tuned to adjust the air-fuel ratio and it seemed to make it more efficient. this was my single best mod simply because I went from 17mpg to 18.5-19mpg.
2) Mallory Hyfire ignition- Some reported little to no gain,but iworked well for me.
3) Tonneau cover (soft with snaps) -consistent 1 mpg
4) Port/polish heads- I have not tried this yet, but I know someone who did and it worked well. It makes sense.
5) Hi flow air filter- I have used K&N filters for years successfully, but recently I've heard excelelnt things about a new filter manufacturer (R2C). They are not oiled like K&N and appear to filter better than K&N.
6) High Quality PLug Wires- I STRONGLY believe in MSD plug wires...especially the Super Conductor 8.5MM ones. I compared them recently against some cheapy ones. The cheapies cost me a couple mpg's.
7) Lowering- My truck is lowered 2 inches in the front and 3 inches in the rear. No significant improvement, but it looks cool. I do beleive there is a slight improvement to be had by lowering though. Less air flow under the car is a good thing.
8) Fuel Rail Cooling- On a returnless fuel system where the fuel enters one side of the fuel rail and has a crossover which allows the fuel to feed the opposite fuel rail, the engine is starved of fuel the further away from the inlet fuel source and the multiple tight bends gettign there creates heat. Newer cars use multiple bank 02 sensors to adjust for this, but it's not optimal. Older vehicles with only two o 2 sensors can benefit from this. Old drag racers used to use "cool cans" which basically is a can that contains ice and the fuel lines go through the can to cool the fuel. I'm currently working on installing a cool can in the bed of my truck, an inline low flow fuel pump and a separate bottle filled with water/anti-freeze. I will be running copper tubing from the gas tank to the fuel rail and back to the cool can. This will reduce the fuel temp and give me a little more hp and possibly better mpg....we'll see.
9) Gear Vendors- They have been out there for quite some time, but overlooked by many. They can convert a 4 spped tranny to 8 speed and allow the engine to run more slowly at highway speeds. I have not tried this yet, but I'm considering it.
10) 100% gas- I measured 0.6 mpg improvement by switching from 90/10 gas to 100% gas.
Hope this helps!
The "fuel starvation" thing is bunk!! Fuel in the rails is at a constant pressure, and the flow is extremely low. Remember we are talking about an incompressible fluid here
You will find that the gear vendors solution does NOTHING for mileage due to gear drag. These units drive a countershaft from the mainshaft via a gear, and back again via a gear. Every gearing costs energy. On many if not most vehicles with an overdrive transmission the energy loss through the overdrive gearing is enough to cancel out any possible gains from running the engine slower. The highest gear should be direct drive, and a change in rear axle ratio should give you the RPM you want in cruise. Optimal cruise should have as few gearings as possible...... you can't avoid the final drive reduction either in the rear end of a rear wheel drive, or in the bull and pinion of a typical front wheel drive.
I have observed this directly both with external boxes like the gear vendors, and with overdrive transmissions. I used a ZT1 years ago (back in the 80's), before we had all the electronic like the scangage.
Now if we could simply shut off the engine during the glide portion somehow, it would really work well. With my Subaru, I could, as it will restart by letting out the clutch, but steering is harder. Why do we need power steering on these small cars??
People have done manual steering conversions. Another option may be the electric power steering found on many modern vehicles; it's not merely an electric motor driving a common power steering pump, but rather a system that provides electric assist directly to the steering. My 2008 VW had it and steered exactly the same with the engine off as on (except it was turned off under about 3mph).
However, in a Pulse & Glide cycle, EOC isn't always very useful. It may take more fuel to restart than to idle for a few seconds, and then there's the issue of driving effort vs. payoff. It is very worthwhile for long glides and is a large part of how I did so well with the VW.
Originally Posted by Howard
On many if not most vehicles with an overdrive transmission the energy loss through the overdrive gearing is enough to cancel out any possible gains from running the engine slower. The highest gear should be direct drive, and a change in rear axle ratio should give you the RPM you want in cruise.
Interesting. I didn't know it was quite that bad. I just finished putting a 5 speed overdrive manual transmission in my 1980 Buick last fall. I wonder if I could have found a non-overdrive transmission and a ridiculously tall rear end...
Any suggestions why overdrive transmissions have become the standard for fuel economy instead of taller final drive ratios and adding lower gears?
I'm guessing that even low "primary" ratios struggle against a "too tall" final drive... that and a dollar will get you a cup of coffee though. I don't know why transmissions are the way they are these days. The concept of a "straight-through" top "gear", with NO gearsets transferring power, and an appropriately steep final drive makes the most sense to me for ultimate top gear efficiency... but that isn't what we have. Also "state of the art" is telling us that more and more ratios "increases efficiency". As far as I can tell, it increases acceleration but not efficiency. For example, in my 5-speed, I almost always skip-shift i.e. 1-3-5, or 1-2-4-5, or whatever, because it is MORE efficient to skip the unecessary gears.
Old EPA 23/33/27
New EPA 21/30/24