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.
Topic: Question for those who know cars. (Read 6627 times)