Good gas tips!

[Alchemy]

Originally Posted by Troberg

It's not heat that runs an engine, it's gas expansion. Case in point: water injection. It increases expansion, but allows the engine to run cooler.

Heat engines, of which the ICE is a type, derive mechanical energy through a change in enthalpy of a working fluid.

The definition of enthalpy considers the energy contribution of both the change in temperature and the change in volume of a working gas.

http://en.wikipedia.org/wiki/Enthalpy

[DrRocket]

Let's cut to the chase. The best way to increase the gas mileage of a late model gasoline powered car is to make certain you keep it maintained, inclucing properly inflated tires. (There's a sticker either on the inside of the trunk lid or the rear of the driver's door edge that tells you the proper tire pressures.) Make certain the front suspension is aligned. Make certain the engine is maintained including tuneups and oil changes. Take all the junk out of the trunk, including those golf clubs you haven't used yet this summer and those tools you're lugging around. (Besides, even if your car did break down, do you really think you could fix it on the spot? Take the average auto engineer and put him/her in one of their products. Have it break down on the interstate. They'll just turn on the flashers and start hiking. They wouldn't even bother opening the hood, because they know there's nothing they could do about it without a diagnostic scanner and computer.) Change the air filter on a regular basis. Smoother driving habits, avoiding the need to "beat" people to what or where ever. Traveling at the posted speed limit. Maybe even a couple of mph slower. Plan your local trips carefully, combining your shopping trips if possible. Drive fewer miles per week. Don't allow your car to sit and idle. You're doing nothing more than wasting gas. Skip the "warm up" during winter. Even on the coldest of days, you don't need to let the car warm for more than 30 seconds at the most before it's safe to drive it. Don't wait for the defrosters to de-ice your windshield. That's what scrapers are for. Besides, it'll warm up faster being driven than if it just sits.

All of the above WILL guarantee you'll use less gasoline per week and save money in your transportation budget.

Not very sexy or exciting. Requires some forethought and planning, things Americans seem loath do to.

There is no device or computer or carburetor or fuel injection system or additive that will get your car to give you incredible gas mileage. If Detroit could make a car that got 100+mpg, would you buy it? You bet you would. Do you think Detroit knows this? You bet they do.

[jimmy101_again]

Originally Posted by Troberg

Scam.

Basically, the lack of efficiency in a modern engine is mostly from friction and inertia in the moving parts, the combustion is very close to perfect. You can test that by sticking a sparkler up the exhaust (keep away from it just in case) and see how little unspent fuel there is. Unless you run it very rich, such on full choke, it's unlikely that there'll be any major flames.

In other words, to increase efficiency, there are two ways to go:

1. Use a more energetic fuel.
2. Use a more mechanically efficient engine design.

The highlighted statement is technically correct and practically wrong and/or irrelevant. Combustion does indeed proceed to nearly 100% conversion (and the catalytic converter makes absolutely sure no combustibles exit the exhaust) but the efficiency of a combustion engine is terrible. A very well designed gasoline engine, running as well as it possible can, only converts about 30% of the available energy in the fuel into useable mechanical energy. The other 70% is mostly wasted heat with some losses to inertia, friction and other things.

So the relevant test is not whether the exhaust gases can still be combusted (since the catalytic converter is there specifically to make sure there is nothing left to combust, but the converter wastes all the energy it releases), the relevant test is the temperature of the exhaust gases. In a "perfect" heat engine the exhaust gases would be at ambient temperature.

Technically, an ICE is a "heat engine", it works primarily by creating pressure using heat. Like Alchemy said, it is a bit more complex than that and you need to calculate the changes in enthalpy (temperature, volume and pressure) to get the details correct. Essentially 100% combustion is pretty much expected in a modern ICE. Deviations from 100% combustion are not the reason ICEs are as inefficient as they are.

A gasoline ICE can be fairly easily converted to burn hydrogen. But hydrogen fueled cars are rarely built that way. Why? Because of the intrinsic inefficiency of ICEs, there is really no way to get much more than ~30% of the energy out of the fuel in an ICE. Hydrogen cars are usually not ICEs, instead they are fuel cells which basically generate electricity directly without going through a "working fluid" or using heat in the process (though they do waste some energy as heat). A fuel cell is typically 40 to 50% efficient in getting the available energy out of the fuel. That doesn't sound all that much better than an ICE but it does represent getting 30 to 60% more of the energy available in the fuel as useable power.

[Troberg]

So the relevant test is not whether the exhaust gases can still be combusted (since the catalytic converter is there specifically to make sure there is nothing left to combust, but the converter wastes all the energy it releases), the relevant test is the temperature of the exhaust gases.

Yep, forgot the cat, I tried it on my Pontiac where I had removed the cat, and it still barely coughed when I stuck a sparkler up the pipe.

I know I simplified things, but the biggest efficiency traps for traditional combustion engines are covered in my simple model.

Originally Posted by DrRocket

Let's cut to the chase. The best way to increase the gas mileage of a late model gasoline powered car is to make certain you keep it maintained, inclucing properly inflated tires.

I can concur with that. I bought some wheels for my car from a friend. While the wheels were stock alloys made for my model, he put on different size tires (225/50R15 instead of the stock 195/60R15). At more than an inch wider, they have considerably higher rolling resistance which dropped my fuel economy by about 5 mpg. When I first put them on the car I ran them at a nominal 30-32 psi. I've recently started running them at 37 psi and *most* of the drop in fuel economy has vanished.

Now, I wouldn't advise everyone to overpump their tires like I have, but running too low definitely hurts your fuel economy.

My buddy in the know just responded ...


Tip #1 - In Canada there is a temperature sensing unit that adjusts the meter to compensate for temperatures changes. If you look at the pump when you fill you can see the sticker affixed to the pump. This ensures accurate custody transfer. Surprisingly there can a 4% difference without the adjustment. Also, the ground changes temperature very, very slowly. Motorcyclists can feel the cold gas tank with their thighs after they fill up on a warm sunny day.

Tip #2 - In Alberta there is no vapor recovery system at the pump nozzle like there is in California (and a few other states). It's built to capture the vapours from your tank as the fuel displaces it - likely a good thing but a pain in the butt for motorcyclists. If there is no vapour recovery there is no need to go slow - unless you have nothing else to do and just want to irritate the people in line behind you. Even with the vapour recovery system it'll make ZERO difference since it recovers vapours - not liquids.

Tip #3 - All vapours are recovered from your gas tank - it is not vented to atmosphere as the author suggests. There is ZERO benefit to filling at half full in terms of losses to vapour.

Extra tip - Regardless when the truck delivers the fuel, it's filtered at the pump, then in your tank, then at your fuel filter. Besides, the truck delivers warm fuel! Get it when it's cheap!!

Usually there is an agenda with these things - especially when it's completely false - like this one is. I'm not sure what this persons agenda is but I expect it's an attempt to slow the service at gas stations. Filling at half speed twice as often would sure slow things down!

Incredible!

[Natalie]

Originally Posted by DrRocket

Take all the junk out of the trunk...
Skip the "warm up" during winter. Even on the coldest of days, you don't need to let the car warm for more than 30 seconds at the most before it's safe to drive it.

Depends on where you live. We keep a winter car kit in our car, which weighs quite a bit, although not as much as a bunch of golf clubs!

How long you need to run your car in the winter really depends on how cold it is. During the last couple of months in Minnesota, the temperature has gone quite a bit below zero (-10 as a high, -20 or -30 at night). When it's that cold a car needs to run a little bit more than thirty seconds. When it's 25 or 30 degrees, you can pretty much just start you car and go.

I also read at some point that it should run park for a bit and then in gear for a bit, but I'm not sure if that's true.

Originally Posted by Natalie

I also read at some point that it should run park for a bit and then in gear for a bit, but I'm not sure if that's true.

I herd that also, it's suppose to warm up the transmission but I have no idea if it's any true.

Originally Posted by damian

Driving around with a full tank is akin to carrying another passenger, in terms of weight.

Which really isn't a concern at all. Gas weighs approx 6lbs/gal and even if we were driving 20 gallon engines if we were concerned about the half tank/ full tank we are looking at a whopping 60lbs/120lbs.

The effect weight has on your fuel efficiency is negligible. According to the federal government for fuel efficiency you can lose up to 2% efficiency with excess weight in your vehicle based on a percentage of your overall weight. The larger the vehicle the less impact but from the studies I pulled off the fed site the only noticeable change was with super small cars.

[snopes]

Angry about the price of gas? Just imagine paying for gas you don't get. Some alert consumers have noticed it over the years: A pump that seems to hesitate a second when the lever is squeezed. Anywhere from 2 to 6 cents tick off before the rush of gasoline starts. That's what happens with a common, hard to diagnose and mostly ignored problem with the "check valve," which is supposed to make sure gas flows at the same time the price meter starts.

But even if your gas pump works, it can still be off as much as $5 for every fill up. Tests by local regulators allow a pump to charge as much as 6 cents more than the gas delivered in a five-gallon test.

http://news.yahoo.com/s/ap/bad_gas_pumps

[FullMetal]

Originally Posted by Natalie

Depends on where you live. We keep a winter car kit in our car, which weighs quite a bit, although not as much as a bunch of golf clubs!

How long you need to run your car in the winter really depends on how cold it is. During the last couple of months in Minnesota, the temperature has gone quite a bit below zero (-10 as a high, -20 or -30 at night). When it's that cold a car needs to run a little bit more than thirty seconds. When it's 25 or 30 degrees, you can pretty much just start you car and go.

I also read at some point that it should run park for a bit and then in gear for a bit, but I'm not sure if that's true.

True, and at around -20 C your car definately needs to warm up longer than 30 seconds. Heck on day this winter (-44 read the thermometer) I was in a rush so I didn't want to wait (most people who idle their car in the winter are usually doing it for comfort I do admit), but I had to wait 10 minutes for the car to allow me to put it into gear! The engine still sounded sick after 10 minutes but I could at least move the stick into reverse at that point so off I went, probabally should have let it warm up just a bit more but I was already late for work. man was I cold that morning, but I slept in and had to get to work...
Not being able to physically move the stick kind of makes it hard to drive .

[Troberg]

True, and at around -20 C your car definately needs to warm up longer than 30 seconds. Heck on day this winter (-44 read the thermometer) I was in a rush so I didn't want to wait (most people who idle their car in the winter are usually doing it for comfort I do admit), but I had to wait 10 minutes for the car to allow me to put it into gear! The engine still sounded sick after 10 minutes but I could at least move the stick into reverse at that point so off I went, probabally should have let it warm up just a bit more but I was already late for work. man was I cold that morning, but I slept in and had to get to work...

You should probably have that looked at. -20 C is not uncommon here in the winter, and we don't let it warm up and it still works nicely. Sometimes, block heaters are used, but that's mainly to make it easier to start and to get a better fuel economy until it's warm. Not being able to shift or sounding sick is not normal, at least not until you fo a furter 20 C down the scale.

[snopes]

Comment: Cheating at Gas Pumps

This is a true story, so read it carefully. On April 24, 2008, I stopped at a Kangaroo BP gas station, located at 1325 Main Street, Cartersville, GA. My truck's gas gage was on 1/4 of a tank. I use the mid-grade, which was priced at $3.71 per gallon. When my tank is at this point, it takes somewhere around 14 gallon's to fill it up.

When the pump showed 14 gallons had been pumped I began to slow it down, then to my surprise it went to 15, then 16. I even looked under my truck to see if it was being spilled. It was not. Then it showed 17 gallons had been
pumped. It stopped at almost 18 gallons. This was very strange to me, since my truck has only an 18 gallon tank. I went on my way a little
confused, then on the evening news I heard a report that 1 out of 4 gas stations had calibrated their pumps to show more gas had been pumped t han a person actually got.

Here is how to check a pump to see if you are getting the right amount:
Whichever grade you are using, put EXACTLY 10 GALLONS in your tank, then look at the dollar amount, if the dollar amount is not EXACTLY 10 times the price of the fuel you have chosen,
then the pumps are rigged. In my case as I said the mid-grade was $3.71 9/10 per gallon, my dollar amount for 10 gallons should have been $37.19.
If I had only check the pump. It doesn't matter where you pump gas, please check the 10 gallon price. If you do find a station that is
cheating, contact the Georgia Agriculture Department, and direct your comments to Tommy Irvin, Commissioner. In other states contact proper authorities.

Please don't delete this until you have sent it to all people in your address book. We need to put a stop to this outrageous cheating of customers. The gas companies are making enough profits at honest rates.

[Roadie]

What? He describes a situation where the calibration of the gallons is possibly incorrect, and then describes how to make sure that the dollars per gallon is correct.

[DrRocket]

Yeah, if the pump is rigged, then that method will show EXACTLY how much you're getting cheated by.

Uh huh. Suuure it will..........

While not unheard of, cheating at the pump is pretty rare. Most states levy severe fines against the stations who do it. So much so it simply isn't worth it. If you suspect something's amiss, a better method would be to take an approved one gallon container that's marked, and put gas in until the pump reads EXACTLY one gallon. Then, look at your container to see where the liquid level is. If it's short, call the state and notify them. 99.5% of the time, it's gonna be EXACTLY right on.

[E. Q. Taft]

Six gas-saving myths

With gasoline prices hitting record levels, it seems everyone has a tip on how to save fuel. Much of the advice is well-intentioned, but in the end, much of it won't lower your gas bill.

[RichardM]

A dirty air filter, that is one that is completely plugged up, will increase the pumping losses in the engine and hence decrease fuel mileage. So having a clean air filter is important.

Likewise, keeping the tires at slightly higher pressure that recommended is also a reasonably good idea. Car manufacturers set recommended tire pressures for comfort, not mileage. Yes too high is not good but you can go higher. Put a line with chalk from one side of the tire to the other going right up the side walls. If the chalk wears on the side walls, you are too low. If the chalk wears only in the middle of the tread, you are too high.

And some cars indeed will get better fuel mileage with premium and some won't. As the acronym says YMMV. Try it and see.
Richard, member SAE and rally racer.

[snopes]

There's this money- saving tip making the rounds down at the gas pump:

You'll get more bang for your buck if you fill your tank in the morning before the gas heats up and expands later in the day.

Wrong.

http://www.sacbee.com/101/story/1130131.html

[niner]

Originally Posted by snopes

But even if your gas pump works, it can still be off as much as $5 for every fill up. Tests by local regulators allow a pump to charge as much as 6 cents more than the gas delivered in a five-gallon test.

http://news.yahoo.com/s/ap/bad_gas_pumps

I'm wondering who has a 416 gallon tank on their car. That seems like an awfully big fill-up. At 6 lbs per gallon, I think it would make sense to run close to empty for a while, although I suppose having to fill up as often as you change oil would be handy.

HenryB

I've been trawling through the 'gas saving tips' etcetc.
I began my own experiment many years ago. 25 actually.
Here's the punch-line:

Turn the motor off.

Most of our driving is local, through familiar territory. Particularly in city traffic, over not so great distances.
If I pull up to a set of lights going red, I mostly have a fair idea how long I will be sitting there. Motor off. Anything up to 90 secs, even 2 minutes at one set. Multiply that by the number of sets of lights.
I have a Mazda3 2.3 turbo. At idle speed, my car does 30 - 35 kph (20mph?). Therefor even conservatively, for every 2 mins I am idling, I could have theoretically driven 1 kilometre. Idle time really adds up.

I keep a log of fuel expenditure. Lip-fill with premium every load so I have 99% idea of usage. Yea yea, I know, all that extra weight, but we're talking a *relative* comparison across distance, and tanks, and the effect of one driving symptom across the 'whole'.
Some tanks I'll thrash a bit, others I'll go all out to set some sort of personal petrol-saving record, and see the difference. It is easily 10percent. In terms of a tank, for me that's up to 50+ k's difference. (which is actually more than 10%)

"I am told" the new manual mini has a 'motor off' function in stop-start traffic, and bmw estimate that turning the motor over when hot uses the equivalent of 6secs of idle. (extra-urban mode?).
I never need to use the accelerator to restart. I used to have a turbo 13b Rotary - 5 motors worth, actually - and while I kept it in tune had no trouble turning the old thing off and on.
When I was 21, I had a Volvo 6 cylinder, that I discovered ran at 18.5 MPG. Fascinated to see if I could do better, (things you do at that age...) I embarked on a radical campaign.. which included turning off going downhills - easy to do in slow moving traffic in Sydney. I got 26MPG. No arguments on the merits or otherwise of this please, I simply did it, and that's it.

10% better fuel economy? That should be easy..

Ak