<P> Diethyl ether, with a small amount of oil, a trace amount of a stabilizer and a hydrocarbon propellant, has historically been used to help start internal combustion engines because of its low 160 ° C (320 ° F) autoignition temperature . Some current products sold as starting fluid are mostly volatile hydrocarbons such as heptane, (the main component of natural gasoline) with only a small portion of diethyl ether, and carbon dioxide (as a propellant). It is often useful when starting direct injected diesel engines or lean burn spark engines running on alcohol fuel . Some formulations include butane or propane as both propellant and starting fuel . </P> <P> Diethyl ether should not be confused with petroleum ether (a crude oil distillate consisting mostly of pentane and other alkanes) which has also been used for starting engines . </P> <P> Starting fluid is sprayed into the engine intake near the air filter, or into the carburetor bore or a spark plug hole of an engine to get added fuel to the combustion cylinder quickly . Using starting fluid to get the engine running faster avoids wear to starters and fatigue to one's arm with pull start engines, especially on rarely used machines . Other uses include cold weather starting, vehicles that run out of fuel and thus require extra time to restore fuel pressure, and sometimes with flooded engines . Mechanics sometimes use it to diagnose starting problems by determining whether the spark and ignition system of the vehicle is functioning; if the spark is adequate but the fuel delivery system is not, the engine will run until the starting fluid vapors are consumed . It is used more often with carbureted engines than with fuel injection systems . Caution is required when using starting fluid with diesel engines that have preheat systems in the intake or glow - plugs installed, as the starting fluid may pre-ignite, leading to engine damage . </P> <P> Starting fluid is not recommended for regular use with some two - stroke engines, because it has no lubricating qualities . The lubricating oil for these engines is either mixed with the fuel or injected near the fuel intake of the motor . There is also a risk of igniting the mixture in the crankcase . Engines that require premixed gasoline and haven't been run recently are especially in need of the mixed lubricating oil because oil can dry off internal parts over time . WD - 40 was previously recommended for use on two stroke engines because it has lubricating qualities, however, the formulation with CO as propellant instead of propane no longer has the same effect . </P>

Where do you spray starter fluid in a fuel injected engine