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In the early morning when the temperature is still cold or cool the fuel in the underground tanks at the service station is more condensed (shrunk), and the fuel in your tank is also more condensed from cooling down over night while your vehicle was parked. So your tank has more room when you fill up and the fuel you put in is taking up less room, and therefore you get the most fuel for your dollar. As you can well imagine the service stations are aware of this and some have actually installed inline heaters on their pumps to try and eliminate this advantage to the consumer. However these inline heaters do little in the cooler or colder temperatures of the early morning. Avoid purchasing fuel in the heat of the day if you can for obvious reasons, but also because those inline heaters tend to further expand the fuel in the heat and that results in you getting less fuel for your money.Another good tip when gassing up is to make sure you never fill your tank to the brim that extra dollar or two of fuel will do far more harm than good. Filling your tank to the brim or topping it off causes the excess fuel to go into your expansion canister and flood it, which will defeat the expansion factor and result in a noticeable reduction in fuel mileage. The other problem with over filling your tank is that most new vehicles have electronic gauges that work with a piece of metal attached to the float arm which slides across the metal contacts of the sending unit indicating how much fuel is in the tank. Topping off your tank can push this contact beyond its limits, resulting in damage to the sending unit and inaccurate readings on your fuel gauge. If you continue to over fill your tank eventually the fuel gauge will stop working completely.Buy your fuel form a station that is consistently busy as their underground tanks are filled with fresh gasoline on a regular basis. A slower moving station will have fuel that has been sitting for a long period of time and this can lead to the fuel becoming contaminated. Contaminated gasoline is less powerful than fresh gas and will result in a loss of fuel mileage. You should also stay away from the independent and cheapest stations. These stations get their fuel from the supplier of the week and cheap fuel usually means contaminated, watered down, or below average fuel all of which results in poor mileage, not to mention what it might be doing to your engine?Don’t buy fuel when the tanker truck is at the station filling the underground tanks, because as he is filling the tanks it’s stirring up years of dirt, sludge, and condensation from the bottom of the tank which will end up in your tank. These contaminates will not only cause a loss in fuel mileage but, over time can seriously gum up your engine. Another good habit to get into is to fill your tank before it drops below the quarter tank mark so you’re not sucking up the sediment from your own tank.Most vehicles these days recommend using regular grade gasoline. Using high grade fuel such as premium won’t result in better fuel mileage if your vehicles octane requirements don’t call for it. To find out what your vehicles octane requirements are look in the owner’s manual it should be listed in there.When it comes to motor oil it is recommended that you use high quality oil that matches the manufacturers suggest grade. This can directly result in a one to two percent increase in fuel mileage.Finally there are hundreds of fuel and oil additives out there most of which don’t do a whole lot and usually cost more than they are saving you. However we’ve researched a number of them and compiled a list of the ones that actually worked. We included in our study cost, savings, will it harm the engine, company background and availability.