David Mc

There are smarter people on this forum that could provide more clarity.

With "Heavy" gas, where the SG is out of specification, the lighter, more volatile, more explosive hydrocarbons have evaporated away. The fuel is likely absorbed water and suffered oxidation.

After our survey, I don't use premium fuel. It doesn't turn over fast enough at the station.

Nowhere Man

The smarter people already disproved your theory

David Mc

If I hadn't been busy I would have checked the RVP also but I guess that's not important either.

Mike Ward

Variations in the SG of a liquid can be a result of many factors- some of them intentionally induced. Hurtling to conclusions as to why such a thing has occurred serves little purpose.

mrtexas

Who is "we" and what SG is too heavy in your opinion?

SG of premium should be heavier than unleaded as higher octane components tend to be denser. Aromatics are higher octane and denser. Alkylate is high octane and not denser but a small % of typical super. Denser is better as you are getting more pounds of fuel per gallon.

David Mc

"We" as in a college project with students collecting the samples. I am the professor.

As shown above, the SG specs are available.

The conclusion of the project was that every sample of premium fuel was significantly heavier than specifications and regular grades were not.

Draw your own conclusions.

mrtexas

Can't say for sure but most likely SG of motor fuels is not a regulated specification. At the refinery I worked at the limit on SUL as far as "heavy" was concerned the limiting spec was a maximum 50% point of around 250F. Most important specs beyond octane are vapor pressure to insure the gasoline will vaporize properly and maximum distillation specs so the gasoline is of the proper boiling point range. Gasoline is roughly 100F-380F boiling point material. Anything beyond 380F is kerosene. We tested for the limiting specs with online analyzers to make sure it was on spec. Didn't have a SG analyzer.

pullin-gs

When I visited San Juan, PR two years ago, I found that the locals truly believed that higher-octane gas would not evporate as fast as regular.
They perceived that because it is so hot in PR that if they 93 octane the gas would not evaporate as much as 87 octane.
So even if they drove an old Buick station wagon, they still got 93 octane gas.

MikeM

It's kinda' looking like if one of the chief cooks and bottle washers didn't check SG, it probably didn't mean much?

mrtexas

The regs primarily have to do with emissions like maximum vapor pressure to reduce hydrocarbon emissions and maximum ppm sulfur to reduce SOX emissions. However octane is watched very closely by the oil companies since higher octane costs more to manufacture. The distillation specs are mostly concerned with making sure the gasoline burns correctly and doesn't diesel. There is a wide variation in allowed distillation ranges except for maximum final boiling point of 380F.

mrtexas

Gasoline and most or all petroleum is sold by the gallon not by the pound so density is not much of a concern.

mrtexas

The best reason for not using super is that 99% of cars don't require it and can't benefit from it. If you don't have higher compression and more advanced timing, the extra cost is wasted. It is a great money maker. The incremental sales price for super say 50ct a gallon is several times the cost to produce it say 10ct per gallon. Good odds for the oil company, eh?

Powershift

I have also found that some oil companies will tend to use less ethanol in the premium gas versus their regular grade. I saw this on a number of Amoco/BP pumps where the premium was listed as reduced ethanol. The specs say "UP TO 10% ethanol allowed." So less can be used at the discretion of the oil company.

Ethanol has an octane of approx 108 and a sp gr of about 0.787

Toluene has an octane of approx 121 and a sp gr of about 0.866

Typical gasoline at the pump has a sp gr around 0.72 and 0.73. This will likely contain some ethanol.

If more of less ethanol is added (up to the max) you can see that it can/will swing the sp gr. This could be some of the variation that you are seeing. Also summer to winter blends can likely add additional variation.

As Mr Texas said, sp gr is not that important to the refiners and oil companies……….so they don't control it. RVP and octane and BP Range are more important to them.

Larry

65tripleblack

Japanese fuel injected cars run better on US gas than US cars.

My deceased aunt's 1992 Honda Accord had been sitting for 7 years with about 3/4 tankful of gas. On a zero degree day in January I put air in the 4 flat tires, cleared the dirt, cat ****, grime from the windows, removed and cleaned the 4 injectors, added 2 cans of "Dry Gas" (alcohol), installed a new fuel filter and battery, fired it up and drove it home from Brooklyn NY to the Jersey Shore.

I forgot to measure the SG of the 7 year old gas before I did these things. It was probably 87 octane, so, not to worry.

SonnyAK

Off topic slightly...Any of you guys use the Pure Gas App?? It's a great tool for locating ethanol free fuel when traveling or in a new location. I generally prefer using a higher octane fuel, but I definitely prefer ethanol free in everything! As far as winter storage, I don't worry about that too much...top everything off and air up the tires and let it sit...

Powershift

I use it (Pure Gas App) a bit. My 1967 currently runs a 50/50 mix of 93 octane ethanol free premium and 110 octane VP leaded racing gas. It very much likes this blend.

However, car can run on 93 octane with ethanol if needed. Car does not particularly like this, but it still goes down the road without pinging. A 1967 327/350 HP car.

Larry

SI67

Dents the bottom of the tank?

Mike Ward

That's more of a 'finding' than a 'conclusion'. It takes quite a leap of logic to go from noting that 100% of samples had an higher than anticipated SG to a conclusion that 100% of high octane fuel is therefore 'bad'.

Poor students.