Good gas tips!

http://www.snopes.com/inboxer/household/gastips.asp

[Towknie]

This thread will help you with the temperature thing. Expansion of heated fuel can occur, but hardly to a measurable extent.

[Eddylizard]

How much fuel could you lose during the filling process due to evaporation? Surely it's a negligible amount.

Also does agitation increase evaporation? If I have a pan of hot (near boiling) water on the stove and I agitate the water, it appears that the amount of vapour is reduced. That of course might not apply to petrol in a fuel tank.

[damian]

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

[Skeptic]

I've been in petroleum pipeline business for about 31 years

I work in a place making circuit boards for cars, but that doesn't make me an expert on cars though.

[jw]

Originally Posted by damian

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

I understand that in small engine cars (like my mazda) this doesn't make that much difference to consumption. However, they only way I can check consumption is to fill the car, drive, fill again and do the math. Unless, someone has another way of accurate checking?

[charlie23]

The only one that rings true to me to any significant degree is #2. I have a wire mesh filter in my fuel tank on the bike and it does indeed collect much more crap after they've just had the tanks refilled.

[Zachary Fizz]

Originally Posted by jw

I understand that in small engine cars (like my mazda) this doesn't make that much difference to consumption.

That seems counter-intuitive to me, jw. Surely a small engine has to work disproportionately harder, whereas a large engine is hardly going to notice?

Years ago I had a 1600cc estate and a 1800cc saloon each of which certainly sounded like the engine was having to work harder (and use more petrol) if I had passengers or luggage. Even a full petrol tank made a noticeable difference.

Now I have large-engined cars, I don't notice any difference to the revs needed to pull away etc, regardless of load.

[jw]

Originally Posted by Zachary Fizz

That seems counter-intuitive to me, jw. Surely a small engine has to work disproportionately harder, whereas a large engine is hardly going to notice?

Now I have large-engined cars, I don't notice any difference to the revs needed to pull away etc, regardless of load.

I agree with your point about a 1600 cc, being less efficient than an 1800cc pulling the same weight car and passengers.

Ok. So a 50 mpg car might do 49 mpg with a full petrol load, but something like wrong tyre pressure, or open windows could have the same effect.
All I'm saying is the difference is very marginal, and not worth repeated trips to petrol stations, maybe wasting even more fuel in the process.

[Keeper of the Mad Bunnies]

Originally Posted by Eddylizard

How much fuel could you lose during the filling process due to evaporation? Surely it's a negligible amount.

Considering most modern stations have a vapor recovery system in place, I would say almost non-existent.

James Powell

[Eddylizard]

Originally Posted by Keeper of the Mad Bunnies

Considering most modern stations have a vapor recovery system in place, I would say almost non-existent.

James Powell

I think that was the point in the OP - the vapour is recovered by the pump mechanisim after it has been metered in it's liquid state and sent back into the station's tanks, rather than ending up in the motorists fuel tank. Poor motorist pays for the vapourised fuel, but the stations retain it. I'm of the uneducated opinion that this is a negligable volume.

[1958Fury]

I'm most curious about #3. People have always told me to wait until I'm almost empty to fill up. Will people ever agree on anything?

Originally Posted by Zachary Fizz

That seems counter-intuitive to me, jw. Surely a small engine has to work disproportionately harder, whereas a large engine is hardly going to notice?

Years ago I had a 1600cc estate and a 1800cc saloon each of which certainly sounded like the engine was having to work harder (and use more petrol) if I had passengers or luggage. Even a full petrol tank made a noticeable difference.

Now I have large-engined cars, I don't notice any difference to the revs needed to pull away etc, regardless of load.

Actually, engines are more efficient the "harder" they work (they don't really work harder, just faster). They also burn more fuel when they work faster, so, its a wash. You get more usable power for the gas you burn, but you burn more gas.

Cars actually need very few hp to operate, the additional power is just gravy. A small engine with four cylinders will dump less fuel in at lower rpms, but needs higher rpms for power, while a bigger engine with eight cylinders will dump more fuel in at low rpms but not need to rev so high. A large engine with higher displacement will generate more torque at lower rpms though, so it will seem more effortless.

Originally Posted by 1958Fury

I'm most curious about #3. People have always told me to wait until I'm almost empty to fill up. Will people ever agree on anything?

Seems you'll always get conflicting opinions on just about anything.
As for waiting until empty to fill up, I usually do that in my car. Unless it's cold in the winter. In that case, most I've heard recommend not allowing the tank to go less than half, as condensation inside the tank can freeze, thaw, refreeze, turngin into water which can cause freezing of the gas lines. I have had this happen before about 20 years ago, but a little gas line antifreeze cured up the problem in no time.

In the semi I drive, the company policy is to fill up when extremely cold when the tanks are half full or so. That is, if you're going to be parking overnight. In Canada, fuel is the "winter fuel" diesel, and it has antifreezing properties, but even then, a lot of trucks can freeze up.

[damian]

Around here, fuel prices are generally higher on the weekend than on a Tuesday. If I fill up on a weekend, I may pay an extra $4 per tank.

If I top up the tank on a Tuesday, regardless of the amount required, that's X number of litres I don't have to pay more for on the weekend.

[DrRocket]

3. Fill up when your gas tank is half-full (or half-empty), because the more gas you have in your tank the less air there is and gasoline evaporates rapidly, especially when it's warm. (Gasoline storage tanks have an internal floating 'roof' membrane to act as a barrier between the gas and the atmosphere, thereby minimizing evaporation.)

There IS a good mechanical reason to keep the tank topped off. Most modern cars use electric fuel pumps located in the gas tank. Because fuel injection systems need more volume and higher pressures to operate, the modern fuel pump runs hotter than the old mechanical engine driven ones of the carburater days, and the auto engineers count on the gasoline in the tank to help cool the tank mounted pump. When you run the tank dry, the pump isn't getting any cooling help from the gas, and runs hotter and wears prematurely.

For cite, I offer this Click And Clack column since most here seem to trust them.


I've been in petroleum pipeline business for about 31 years, currently working for the Kinder-Morgan Pipeline here in San Jose, CA.

My Aunt used to work for AT & T for 27 years, but she still didn't know squat about how a telephone worked.



4. If you look at the trigger you'll see that it has three delivery settings: slow, medium and high. When you're filling up do not squeeze the trigger of the nozzle to the high setting. You should be pumping at the slow setting, thereby minimizing vapors created while you are pumping. Hoses at the pump are corrugated; the corrugations act as a return path for vapor recovery from gas that already has been metered.

This may be a California thing. I remember those corrugations, from my last trip there but the hoses are corrugated on the outside only, they're still smooth on the inside. The outside corrugation is the vent hose return line wrapped around the outside diameter and covered with a thin sheath of rubber. (I remember a cuff used to catch vapors at the handle too.) The inside is still smooth. Hoses in other parts of the country do not have the "corrugated" look. They don't here. Engineering wise, it wouldn't make sense to put a corrugated surface on the inside of a hose. It would create too much pumping inefficiency.


I've been in petroleum pipeline business for about 31 years, currently working for the Kinder-Morgan Pipeline here in San Jose, CA.

My Aunt used to work for AT & T for 27 years, but she still didn't know squat about how a telephone worked.

[snopes]

As temperatures rise in underground storage tanks, gasoline loses energy, but fuel prices don't flex to compensate consumers.

http://www.latimes.com/classified/au...,1193672.story

[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.

[Alchemy]

Originally Posted by Troberg

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.

About 60-70% of the energy generated by the combustion of gasoline in an ICE is lost as waste enthalpy in the exhaust or drawn away by the cooling systems. Friction losses are less than 5% for an engine in decent condition.

Even the most efficient fuel-burning heat engines max out around 50-60% thermal efficiency. Total combustion doesn't mean you get to use all the energy generated by that combustion.

[Troberg]

About 60-70% of the energy generated by the combustion of gasoline in an ICE is lost as waste enthalpy in the exhaust or drawn away by the cooling systems. Friction losses are less than 5% for an engine in decent condition.

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.