Topic: Question for those who know cars.

[mathcubeguy]

so did you save money by using a better gasoline?

[EE]

I honestly did not notice much of a difference in my gas mileage. Not until today when it all of a sudden jumped up from the old 270'ish mark. I think the extra $2.50 or so a tank was worth it for the horsepower gains and the smoother running of the engine so if these mileage gains stay thats just a bonus on top of an already happy customer of 91 octane gas. I have been temped to try some octane booster but $7 for one bottole and to only raise my gas to about 94 or 95 octane I dont think is worth it.

[JMM]

Consumers beware, a lot of those ädditives are nothing more than cleaners and snake oil. When I get back to Austin, I will ask my ex coworkers that are ASE master techs, there are some additives (pricey) that will put you near or over the 100 octane mark!  

[JMM]

On a side note, treasure what fuel prices you have in the good ole USA, PEMEX is the only gasoline company allowed in Mexico (govt. owned monopoly), and Dr. Valles put a quarter tank in his old Nissan Sentra (Tsuri is the name of it here), the cost for a quarter tank of gas? Try 10 frigging dollars! Yet the Mexican people do not benefit from it like we do from the Fed taxes on our gasoline sales.  

What's even worse, is the population is not allowed to know where all that money is going, at least I can look at Veteran Affairs and see their budget and EXACTLY what is going to where in each subdivision of Veterans Affairs. Treasure your freedom peeps.  

[Barabbas]

OK, Batman.  Riddle me THIS:


My '88 Mazda RX-7 (Fuel Injected 1.3L Rotary) runs great... Sometimes.  Since last Winter, I've found that it absolutely HATES certain gas, but then I fill up with a nice fresh tank from one of two local stations and it purrs like a kitten again.  And I don't mean that it just runs a little rough; it coughs, sputters, doesn't want to start or idle.  Only under hard acceleration and cruising does it do OK, and even then I can tell it's not right.

It's not water in the line, or a dirty fuel filter, or O2 sensor....  I'm beginning to believe that there's a bad sensor in it that isn't compensating for oxygenated 'Winter Blend' gasoline, even though I was getting bad tanks all through the summer from most main-line stations.  This morning I filled up at the local Getty that it's loved for the past year and found that it doesn't like that one anymore, either!

Does anyone know anything about oxygenated gasoline, or what sensors in a car would interact with it?    

[JMM]

Gas with Oxygen added gives a more complete burn in the combustion process. Fuel injectors use O2 sensors which regulate the amount of fuel and air going into the engine (they sense when too much or too little is going through the exhaust and cat converter, hence many cars nowadays have not one, not two, but three O2 sensors. Imagine that! Of course, all this means nill as there are many sytems involved, and if your ECU has a malfunction somewhere, every other system involved in the combustion process may be running perfect, but be getting the wrong info because of a bad ECU.

Rotary engines are great, but they pollute more than normal gas cylinder engines, is why Mazda had to discontinue the RX-7 series for years, they could not make it a cost effective sports car and meet emmissions standards for the U.S.

Sounds like your problem is in the fuel delivery process, and there are many components involved. I usually get a Haynes manual before anything on cars I'm not familiar with, why? 15 bucks or so and is so much better than Chilton's, plus they have actual photographs of what you look for, not some stupid diagram. At the beginning of the book is troubleshooting symptoms with steps, just like a doctor uses when making a diagnosis on a patient.

There are many Mazda fans out there, look for websites that have forums like Taldren, where you can ask questions and get expert Mazda answers. Like I told Towelie and EE, yahoo chat also has an automotive section as well. I was never an ASE master tech, I worked under them and learned, but to be their level you are looking at 8-10 years of rock solid work and using your noggin.  

[Iceman]

JMM,

That'd be great advice, for any car besides the RX-7.  my friend just got one (forget the year) but he has to buy 100 or 110 octane plane fuel for it to run nicely.  It's just the engine, it's very tempermental.  Thats my exprience with it anyways, you could still very well be right!

BTW, if you're looking for 100 or 110 octanes, go to your local airport and ask around, there'll be some fuel trucks.  Expensive stuff though, but you can't beat it. Also, it's green or blue, so don't freak when you don't see normal 'gas' being pumped into your baby.

[Toten]

EE,

Mileage will be affected by many things.

1) octane of the gas - higher burns hotter per gallon making more power per displacement, water content in the gas per mass robs you of power in the combustion process, alcohol gas mixtures do the same thing as alcohol burns hotter and cleaner but at far less BTUs per pound of fuel, hence u will suck down more fuel per HP of output
2) stop starts - the more cold starts you do chews thru gas as the engine has more load on it as all the lube is colder causing more inefficiency in the engine (hence warming up the engine)
3) traffic loading - the more speed changes you do the more gas you consume to reaccelerate to cruising speeds (lead foot syndrome)
4) Degree Days - colder air is denser and unless u have a boost system on your car then it must suck in make up air, my passat 1.8T is turbo and makes its own boost as needed.  HOT HUMID rainy summer days make all engines lose power, as the fuel content is partially used up to heat moisture which is really a heat sink in the combustion process, and the tempurature of the incomming air drives its density down making for lower compression in the engine.  Compression ratio doesnt change (unless u have thrown a connection rod), the TDC compression value will be lower.
5) Tire Condition - tire pressure is affected by ambient temperature,  controlling tire pressure is a often overlooked way to conserve fuel.  Under inflated tires cause pull on the wheel alignment wasting inertia, as well as overworking of the tire membrane.
6) Wheel alignment - Some thing as simple as dinging the curb can throw out ur wheel alignment, toeing of the front end can cause snowplowing on the tires causing wasted intertia.
7) Wheel Balance - again throws out the stability of the platform causing occilations that take inertia from the car.
8) Fuel System - The O2 sensor, Exhaust sensor, fuel pump pressure, timing, injection spray, type of spark plug etc etc can cause ineffiencent combustion, improper air fuel mixtures for LEL.
9) Thermostat Setting - Another thing that really kills some vehicles (espcially OTTO DIESEL Diesel engines) is the coolant temperature.  Some engines are actually OVER COOLED to the extend that combustion, lube circulation and bearing drag coefficent actually suffer.  Thats one of reasons you see cold application transport trucks actually block off the radiator in winter months.
10) Air Intake - Most cars today take the air into the intake manifold via an opening usually located below the driver side head lamp.  This area is prone to road dirt (bugs, dust, salf etc) and feeds this up to the intake manifold prefilter.  A partially dirty filter is actually better at filtration than a clean one, BUTas the filter cruds up the differential pressure across this increases to the point that the engine will begin to sputter due to insufficient inlet air pressure.  THE GOOD NEWS IS .... a filter clogged so badly can actually rupture spattering dirt into the engine, assuming it survived the filth, then the inlet pressure differential is dramatically reduced actually giving more availabe horsepower.
11) Cruise Control - This nifty feature on ur car SUCKS DOWN GAS !!!!!  The cruise control is set to keep a constant speed NOT a constant fuel consumption.  Cruise control actually pumps the gas peddle like a mad man to maintain a constant speed in the car, in so doing mileage can vary wildly.
12) Ring Tolerence - Related to engine temp (as well as overall engine wear) leakage past the piston rings can lead to engine oil being burnt with the fuel. (ur blue smoke cars)  I will assume ur car is not white smoking (head gasket gone with coolant getting into th cylinders) or burning black (fubar air fuel mixtures)

These are a few that can affect mileage that are relatively controllable.

BTW
on 50L of fuel (91 octane) (13.22gallons) i get
650 Km hiway under my control - 406.25 miles  (31 mpg)
570 Km hiway on cruise control - 356.25 miles (27 mpg)
480 Km city driving my control - 300 miles (23 mpg)

In short driving at a constant speed with you foot in one position on the peddle with proper maintainance on your car saves a crap load of fuel per distance.