What type of gasoline should we use in our cars? Well, lots of people have opinions. Some are based on experience, others are based on long-held beliefs that have been passed down from father-to-son, and so on. To help our engines last as long as possible, we need to help them warm up as quickly as possible. Does the gasoline that we use in our cars have any effect on this warm-up cycle? You bet it does! Your gasoline has a direct bearing on the amount of time your car needs to reach Normal Operating Temperature (NOT). The more volatile the gasoline is, the less time it takes for warm-up. Volatility is a measurement of how easily the gasoline will ignite.




AREN'T ALL GASOLINE'S THE SAME?

"If all gasoline's are the same, what difference does it make what particular brand of gas I use?"

Well, all gasoline's are not the same, and the brand of gasoline that you use in your vehicle can make a startling difference in all aspects of your engine's performance. Gasoline volatility is determined at the refinery and is directly related to the distilling process. Specifically, the larger the percentage of the gasoline that is distilled below 100º C, the more volatile the gas will be. The lower the volatility of the gas, the longer it takes your engine to warm up, thus creating more engine wear and tear. Unfortunately, the volatility ratings of gasoline's are not listed anywhere on the gas pumps, but through experimentation you can find a gasoline that is well-suited for your car.

WHAT ABOUT NON-BRANDED GASOLINE'S?

There are plenty of places where gasoline is sold and the brand name of the gas in not displayed anywhere on the location. There can be a couple different reasons for this.

Maybe the gas is being sold by one of the larger 'wholesale' clubs. They do not necessarily get their supply of gasoline from the same source each time they replenish their bulk supply. Therefore, one tanker-full of gasoline could possibly be a high quality fuel with a high volatility rate, and include a nice, robust additive/detergent package, and the next tanker could be delivering a lower quality fuel, with a lower volatility rate and maybe a lesser additive package. Since these types of places do not usually advertise any specifics about the gasoline they sell, there is no standard that they can be held to. Or at the minimum, a very low standard. On the other hand, there are several chain-stores that sell gasoline under their own brand name. Even though it may say it on the pump, there is really no such thing as '7-11' brand gasoline. Most convenience stores do not operate refineries, obviously, so they must buy their gasoline stocks from another source. The same conditions apply here, for the gasoline is not typically advertised with any specific performance or additive package, so it is really just a big crapshoot as to the quality you are getting.

STICK WITH BRAND NAMES

A well known branded gasoline will usually cost a few cents more per gallon than the cheap-o place down the street, but is there a valid reason for this higher price, or is it just the gasoline company making extra money?

Most of the well-known branded gasoline's will list somewhere on their pumps the benefits of using their particular brand of gas. And it isn't always just advertising rhetoric, either. The major gas marketers most often have a sophisticated detergent/ additive package installed, as well as having a uniformly higher volatility rate. This is good news for your engine, indeed.

ARE DETERGENTS REALLY NECESSARY?

Absolutely! A gasoline with a proven fuel-system cleaning additive (detergent) is a must. The detergent effectiveness can be seen and measured in fewer deposits in the carburetor and fuel system.

The upper cylinder area of the engine also benefits. Eliminate deposits and you eliminate one source of wear and tear on your big-dollar performance motor. Sensitive areas for deposit formation are carburetors, throttle bodies, the carburetor idle/progression circuits, PCV valves, and EGR systems. Deposit build-up on any of these areas can have a substantial effect on your air/fuel ratio, and therefore fuel economy, overall engine performance, and emissions. Of course, anything that can have those kind of effects will also lead to increased engine wear and tear. The gasoline that you use should definitely have a fuel system cleaner in it.

WHAT ABOUT POUR-IN DETERGENT ADDITIVES?

A good quality fuel system cleaning additive that you pour into your gas tank during a fill up is an excellent idea if you want to keep your infrequently-driven muscle car's engine in top shape.

However, be careful not to 'over-dose' the gas! If the product calls for 1 oz. per every 2 gallons of gas, that is the ratio you should use. If you double up on the recommended dosage, you can drastically lower the volatility of that tank of gas, seriously affecting the performance of the engine. In addition, to much detergent additive will lead to spark plug fouling, another situation that can lead to poor engine performance and increased wear and tear. And if the product is labeled for 'every 3,000 miles' or 'Once a Year', then it is the best to stick with that recommendation. Even if the over-use of the product causes no harm to the engine, it is just a waste of money if you are deriving no benefits from its increased use.

WHAT ABOUT HIGH OCTANE GAS?

"If I use nothing but 93-octane gas, doesn't that keep my engine cleaner, without having to worry about all those additives?" Unfortunately, the answer to that typical question is a resounding 'No'.

What is octane? Octane is a measurement of the gasoline's ability to resist engine knock. It is represented as a number, and the higher the number, the more resistant to knock the gasoline is. Thus a 93-octane gas will resist engine knock better than an 87-octane gas.

The number that is most often posted on the pump is known as the 'Pump Octane'. Pump octane is simply the 'Research Octane' plus the 'Motor Octane' divided by two. Octane is of vital importance, in that it allows the engine to run smoothly and without knocking. This is important because engine knock, engine 'run-on' (dieseling), and upper cylinder noise due to using too low an octane of fuel can cause eventual and severe engine damage. Always make certain that the gas you are using has sufficient octane to run your engine without knocking. The refining processes used to make the 'modern' unleaded fuels do not allow a high octane to be achieved as easily as when leaded gas was common. That doesn't mean that there aren't high octane unleaded gasoline's available; there are. They are just much more complicated, and therefore expensive to produce.

O.R.I. - WHAT IS IT?

As your 'street-machine' engine gets older, and as the natural wear process grinds out its eventual toll, it will require a higher octane fuel than when it was new. Even though engineers don't fully understand why this is, they have a name for it: 'Octane Requirement Increase'.

ORI is a natural occurrence in every engine, so don't be too terribly alarmed if the octane that was recommended for your engine when it was brand-spanking new doesn't seem to be able to keep it from knocking a little. You just need to move up one grade of octane when you purchase your next tank of gas, that's all.

"SULFUR?  WE DON'T NEED NO STINKIN' SULFUR!"

To paraphrase Tuco from 'The Good, the Bad and the Ugly', sulfur is not a good thing for your engine. Unfortunately, there is a tremendous amount of sulfur in the raw crude that gasoline is refined from.

Fuels that have a higher sulfur content will, when burned, produce acids that eat at cylinder walls and pistons. They will also leave a very abrasive residue that can cause extreme wear in moving parts. Purchase the highest quality fuel you can afford, and your muscular power-plant will thank you for it with long life and smooth operation.

A relatively modern complaint that a lot of newer-car owners gripe about is that 'rotten-egg' smell from their exhaust. Catalytic converters have made this unpleasant smell even more noticeable in some cars. Where does the smell come from? From the sulfur in the gasoline…and all gasoline's have some sulfur in them. After the gasoline is burned in the engine, the exhaust finds its way to the exhaust system, where it combines with fresh air (oxygen) and it undergoes a chemical change. The converted sulfur is released into the air in the form of Hydrogen Sulfide, a gas to which the human nose is very sensitive. The more oxygen in the mix, the stronger the smell.

None of this is particularly harmful to the engine or the emission system, but that doesn't make it pleasant for your nose!

• Experiment with different brands of gasoline. One may have less sulfur in it than another.
• Be certain that your ignition timing is set correctly.
• Go easy on the full-throttle starts. Lots of unburned gas dumped into the exhaust stream makes this problem worse.
• Smaller sized primary jets in the carburetor will alleviate some of this also.

WHEN IS THE BEST TIME TO BUY GAS?

Believe it or not, there is a best time of the day to buy gasoline. Gasoline expands considerably when it is warm, so if you fill up in the hottest part of the day, like 'High Noon', then you are not actually getting as much gas as you would if you were to fill up in the mornings or evenings. Try to purchase your gas during the coolest times of the day, and you may save a few cents here and there. Every little bit helps, right?

And you should NEVER buy gas while a tanker-truck is there filling up the tanks, or of you happen to see one leaving having just done so. The gasoline that is being pumped into the underground tanks has a tendency to stir up any sediments that are in the tanks, which can then end up in your gas tank. We don't want that, now do we?

LEADED GAS - ESSENTIAL FOR OLDER CARS?

Ever since the EPA required that the poisonous lead content of gasoline be lowered, and eventually eliminated, all of us muscle-car owners who have classic cars designed to run on high-octane leaded gasoline have been worried over the effects of using low or no-lead gasoline in our babies.

For many years, Tetra-Ethyl Lead (TEL) was used by refiners as a cheap and easy way to boost the gasoline's octane rating. Coincidentally, it also helped to lubricate the upper cylinder area of a car's engine. It is this lack of lubrication that has so many classic car owners worried.

During combustion, TEL, in the form of 'lead salts' is deposited on or around the valves, valve guides, and most importantly, the valve seats. It acts as a buffer against the constant metal-to-metal contact as the valves close against their seats. Gasoline exploding in the cylinders constantly replenished this lead coating. Without lead, these valve seats can recede into the cylinder head. If this happens, engine compression and performance suffer, and can only be restored through an expensive engine rebuild.

Ford Motor Company recommends leaded gasoline for any of its vehicles built prior to 1975, while General Motors claims that any of its vehicles manufactured before 1971 need leaded gasoline.

If your hot-rod has its original engine, with the soft-metal valve train components, consider:

• Monitoring your driving habits closely. Keep your speed under 50 MPH as much as possible, and avoid prolonged driving in high heat, and avoid overheating the engine.
• Try to keep the RPMs under 2,500.
• Don't do a lot of unnecessary full-throttle take-offs.
• Consider the use of one of the lead-substitute additives available at just about any auto-parts store.

Testing has shown that the lead-substitute, when used as directed, will slow down valve recession, but it will not halt it completely. Further testing showed that when used at four times its recommended dosage, valve recession was stopped completely. However, massive and rapid fouling of the spark plugs was the result.

Of course, if your engine has been rebuilt, then you have nothing to worry about in this regard. The components used in the manufacture of engines are now made with hardened metals that are almost totally impervious to the lack of lubrication from using no-lead gasoline.

So even though it seems like 'all gas is the same', there are some real differences. And with a little judicial selection on your part, you will be sure you are using the best gasoline available for your Pride and Joy!





Kit Sullivan is a 15+ year automotive lubrication engineer and a classic and muscle car enthusiast and collector