The Stovebolt Site Forums The Shop Area Engine Shop Gas the good stuff??

HI...I was filling up the Chevy 235 3100 with a medium grade gasoline. Out comes the manager from the store (76) and he tells me that because of the lousy gas here in N. California I should only use a supreme grade of gasoline in "my collectors vehicle"(not a racing fuel like 100 octane) OR I should mix half and half of medium and supreme. I said thanks and I will do that next time???? OK, I don't think I have harden valve seats(this is a 1957 engine)he said the supreme grade would be cleaner burning and better for the plugs and valves?? Was/is he correct? I've done the technical reading but what about you who have driven with a mix or straight supreme is / was he correct? Thanks, Steve

Your truck was designed for 75 octane gas or less. Difference in grade is usually just octane rating. Regular 87 octane is fine.

He's just trying to upsell you. Even the mid grade is more than what your truck calls for.

Thanks guys...he was an honest guy (I think). He was really concerned about our truck. He told us he owned an old Willy's. I think with all the confusion about gas in this state and the new ridiculous diesel laws everyone is try to protect their vehicle best they can.
Cheers, Steve

Why is the gas lousy in your area, is it tainted, or does the guy just think that it is.
Gas is gas and all comes mostly from the same place.
Their are some brands which add additives to their gas but for the most part all the advertising claims for "better performance", "ultra clean burning" are just that... advertising claims to suck customers in. And a lot of people believe it.

I've known some people who burn 91 octane in their car thinking it's better gas, even though the required octane for their car is only 87.

The gas we burn today burns hotter than the gasoline of olden times and may cause some valve issue to develop over time if the valves in your older motor have not been upgrade. The metal used for valves and seats was not designed for that added heat that our gas burns at today

Dan

A lot of it depends on how much difference you pay for the higher octane product. In the Texas Gulf Coast region there is a 10 cent spread between 87 octane and 93 octane premium at the rack. My dispensers blend the 2 to make 89 octane midgrade. In order to be classified as premium, the 93 octane must contain twice the detergent additive as 87 octane which is a big plus with EFI engines. If you take a look at these DOE figures by clicking on the regioun PADD 3 is the Texas Gulf Coast. http://tonto.eia.doe.gov/dnav/pet/pet_pri_gnd_dcus_r30_w.htm Historically our area is the cheapest in the nation. This is due to fierce competition. Federal motor fuel tax is the same all over the US. State tax varies from state to state.

This may help:

http://www.thecarburetorshop.com/Octane.htm

Jon.

My understanding is that the tetraethyl lead added to gasoline years ago was used to boost octane, but had the unintended side effect of lubricating the valve seats. The octane available in standard gas is now quite high without the lead, and there is lots of evidence that modern unleaded gas does not usually do significant damage to non-hardened seats, but the lead additive is a good way to prevent valve problems. I wonder what the final octane would be for 87 unleaded + lead additive? probably overkill.

By the way- "mid grade" gas is just an in-the-pump 50-50 mix of the low grade and high grade gasoline- If this guy says the low grade gas is crap, so is the mid grade.

-Warren (squarenutz)

A reliable source told me one time, and correct me if I'm wrong....

Premium gasolines have higher levels of octane, lower grade gasolines have less... this we know, but gas sold at discount stations, for less price, than say, Shell or Mobil, usually are fuels that are transported in "Multi Use Tanks".

This is where the same tank is used for Kerosene, Diesel, and other petrol products. The reason it's discounted is that trace amounts of other fuels can be found in the gas, therefore decreasing it's purity. (And sale price)

In general, the fuel quality has decreased in the past few decades, and with the introduction of Ethanol, it's even worse.

My two cents.

Skidmarks, there is no validity in the statement referring to "Multi Use Tanks" The same carriers transport for majors such as Shell and Mobil as for unbranded marketers. Most carriers use 4 compartment tanks. If you look at the drain valves, they have signs which they change to help remind the driver what is in what compartment to prevent cross dumping. It is not uncommon for a carrier to transport a straight load of unleaded for Shell and then transport a compartment of Diesel one of premium and the rest unleaded for Chevron. Oil companies have exchange agreements with each other and each companies proprietary additive is injected at the loading rack. Unbranded gas comes out of the same loading racks. However it contains only the minimum additives to meet mandated specs. Branded gas has detergent additives which are very important to EFI engines. I am 66 years old and still operating a gasoline distributorship which was started by my father in the 1930's. I deal with transport loads of gas and Diesel daily.

What crenwelge said. When I drove transport back in the 70s when you emptied out the tank truck, you might have a gallon or two residual product. Even in a small 500 gallon compartment the contamination is minimal. In terms today octane is misleading. There is no lead in todays gasoline, and the term octane refers to a lead compound used in the additives of earlier formulations of fuel. If my facts are off feel free to correct me.

Today's tankers drain much better than they did in the 70's. If you look at the discharge lines, they have much more slope. This was mandated by the shift to unleaded gas in Sept 1975. A gallon of leaded in 1000 was considered too much. Todays tankers drain completely. This is also necessary because of the switch from low sulfur Diesel <500 to <15 ULSD. It doesn't take much low sulfur to make a sample go over 15 ppm. I was able to get leaded gas out of the refinery in Big Spring, TX until the early 90's. Until 1998 I splashed in lead substitute, but that became illegal about then. All additives now have to be injected. There isn't much demand for that type of fuel because in the past 12 years, most vehicles that required leaded gas have became play toys anyway. The octane rating we now post in the US is an average of motor octane and research octane. Octane ratings jumped drastically during the 50's going from 75 to 100 in 10 years. And it varied from region, higher altitudes requiring lower octane. In in answer to the original question, yes 50's 6 cylinders will run fine on 87 octane.

The multi use tanks statement I made was in relation to tanker ships, not service station delivery tankers.. I should have clarified that. The tanks on ships that bring the fuel into the country.

I don't know personally, don't shoot the messenger.

Octane rating is a fuels resistance to detonation or pinging as compared to a standard. The standard used is iso-octane, which gives it the value of 1.0, or as we know it, an octane rating of 100. If a fuels anti-detonation characteristic is better than iso-octanes, the fuels octane rating is above 100, if a fuels anti-detonation characteristic is less than iso-octanes, the octane rating is less than 100. There are two common methods to measure a fuels octane rating, the motor method and the research method. The common octane rating we're familiar with is the average of these two octane rating methods, R+M/2 or research plus motor divided by two. The motor method to determine a fuels octane rating is probably the most accurate. In this method a variable compression single cylinder engine is used to test a fuels detonation characteristics. The outside of the cylinder sleeve is threaded, and the cylinder head assembly essentially screws over the outside of the cylinder. To increase the compression ratio the cylinder head is screwed further down the cylinder, toward the piston, and to decrease the compression ratio the cylinder head is unscrewed from the cylinder, away from the piston. The engine is baselined using iso-octane and the compression ratio is adjusted just to the point of detonation, or adjusted to an octane rating of 100. The engine is then fed the test fuel and the compression ratio is readjusted to the test fuels point of detonation to determine it's octane rating. Gasoline is not just one hydrocarbon, but a whole bunch of different ones blended together. The research method is basically an octane estimate based on previous motor tests of the different hydrocarbons used in a particular gasoline blend. Tetraethyl Lead was first introduced in the early twenties as an octane increaser for gasoline by the Ethyl corporation. Lead has nothing to do with iso-octane itself, what it does do, is increase a fuels resistance to detonation, ie improving it's octane rating, of course it also causes brain damage. A couple of other ways to increase the octane rating of gasoline is to change it's molecular compound by catalytic cracking, this method essentially turns a lower octane hyrdocarbon into a higher octane hydrocarbon through the use of super-heated steam and a catlyst. The other common method is to blend the gasoline with another fuel that has a higher octane rating most commonly ethyl alchohol. When it comes to rating fuel as regular, midgrade, or premium, most consumers only consider the octane rating. As others have pointed out, it also includes other additives which can be brand specific. If you want to see what several auto manufacturers recommend, go to www.toptiergas.com.

John