Grades of Gasoline


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From Bill:

All gas comes from basically the same sources and therefore is always the "same" gas chemically. Some companies add various ingredients
for various reasons. Shell and Chevron add detergents and say so at the pumps... these detergents are supposed to keep the fuel system, cylinders,
and exhaust cleaner than gas that does not have them. Some companies add various anti-smog, anti-pollutants, mileage extenders, and etc., because of regional laws.

There really is such a thing as "bad gas". I do not know if your problem is caused by bad gas but here is what I know.

Gas can be "bad" for various reasons. All petroleum products will deteriorate over time unless certain preservatives are added. People who
store fuel for long periods of time add fuel preservatives to their storage tanks to keep their gas (or other petroleum product) from going bad. Gas can also become contaminated for some other reason... for instance someone could put a foreign substance in your tank... or any tank for that matter.

One of the most common contaminants is water. Water can get into gas in various ways... the most common is when tanks are not kept full... refinery tanks have a top that floats on top of the fuel so that there is never a space between the surface of the fuel and the top of the tank where
condensation can take place.

Water usually gets in fuel when there is humidity and the fuel tank is low. Warm moist air enters the tank in the heat of the day and condenses on the
walls of the tank at night running down into the fuel. I think you may know the result of this kind of contamination.   

From E:

There are all kinds of fuels and different grades of all of them floating around. I just wanted to set the facts straight about a few things and give some useful information about fuels. I am going to discuss low grade gas, high grade gas, alcohol, and diesel fuel. 

First low grade gas

Low grade gas is cheap, so everyone likes it. Is the most fast burning fuel you can get. It burns faster and hotter than the other fuels. It tends to burn unevenly and leave lots of deposits in your engine. 

High grade gas:

High grade gasoline is made of longer molecular chains. Gas is usually rated in octane's which is some what misleading (see below) because octane's are a 8 molecular group chain in the petroleum family. It is the slowest burning gas, giving you a longer, and more even power stroke. It also burns colder, which is especially important for those of you that live in hot areas or if your car is prone to overheating. Running high grade will keep it cooler. It also tends to burn more completely, leaving less deposits and not sending as much back out the tail pipe. 


Alcohol is a alternative and often an additive to gas. It is slower burning than gas. It tends to have a lower ignition point (starts burning at a lower temp). It is more environmentally friendly because it produces H2O(water, and CO2 or carbon dioxide as opposed to gasoline's carbon monoxide (poisonous). The water it produces is less than favorable because it tends to rust things in the exhaust. Holes must be drilled for it to drip out of so it does not pool in low spots. This makes keeping these vehicles quiet a real problem. That is why they are mostly seen at race tracks, and on boats. . Conversion kits for cars can be purchased. Usually it involves: a new exhaust manifold, carburetor adjustment, a heavier flywheel holes drilled in the exhaust and a timing advance. 


Diesel fuel is the slowest and the coolest burner. Because of this diesel engines tend to have the a very long stroke on them. And because it is the coolest it is also favored for engines that have to run for long periods of time without stopping. Diesel engines tend to be slower to accelerate, that is why the turbocharged diesel engines are very popular. Octane Octane tends to be misleading because if you go down to your local automotive store they will sell you a little bottle of "octane boost" it actually contains no gas parts of products, it is alcohol. By mixing alcohol with gas you slow down the burn, and cool it some, giving the same or near results as buying a higher grade of gas. But the alcohol is cheap, you are paying for the cool looking bottle. I have a friend who has experimented with putting a little diesel fuel in his gas when he fills up. the results were surprisingly great. I don't necessarily recommend this but it worked good for him.

This page last updated June 5, 2001.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club