Previous reading elsewhere said using lower octane works fair by computer adjusting timing, giving weaker performance. Higher octane would not improve mpg. Threads here indicate most Forum writers prefer premium, many claiming measureable mpg increases.

We have choice here of 87/89/93 octane. My 1997 XJ6 was OK with 87 with sedate driver, giving 23 mpg highway. Now have XJ8. Jaguar suggests 91 min. Thoughts?

 

all cars will work with lower octane

but you answered your own question, the ECU will adjust to the lower octane by giving weaker performance...and not to forget lower octane will contain contaminants that will clog pipes, injectors, etc.

Higher octane may or may not improve mpg, but lower grade WILL decrease mpg.....so whatever few dollars you save at the pump, you end up filling more...thus costing you the same if not more in the long run.

im just gunna say this......you bought a Jag, with a wonderful V8 engine...it only costs a few bucks more to fill it up with higher octane. its not worth saving a few bucks for sluggish performance and the possibility of damaging your engine.

 

Sorry, this is absolutely false. How would you explain the millions of cars that operate just fine on the lower octane gas they were designed for?

Octane level of gasoline has nothing to do with 'quality' or 'purity', simply how well it resists detonation.

There's nothing to be gained by exceeding the OEM spec of 91 AKI. Whether your car achieves lower mileage or reduced power seems to depend on the individual driver or even from car to car and area to area. There's no evidence that it will do damage.

 

interesting, i knew octane has nothing to do with purity, but at the same time i was under the impression that lower grade fuel may contain some contaminants

thanks for clearing that up.

 

I endorse the "octane level has nothing to do with contaminants." Use what the Jag engineers want you to put into the tank. I higher octane level than specified will not improve performance. Octane level is a measure of the fuel to resist detonation originally on a scale from Zero (Jefferies Pine n-heptane C7H16) to 100 (2,2,4-Trimethylpentane). Since we got rid of TEL (tetraethyl lead) things have become more complicated for the chemists, hence the isomer towers at refineries to increase the hydrocarbon chain length and therefore octane rating. Incidently, adding ethanol (alcohol, not the drinking stuff) to petrol increases the octane rating marginally but it lowers the calorific value of the fuel--lower mileage. It also has an affinity for water (corrosion issues) and eats certain types of rubber seals and hoses -- bad.

 

Very well said Boost

 

All very true- and I'm no supported of ethanol infused fuels but three additional points need to be made.

-E10 fuel has 97% of the energy of pure gasoline/petrol. Given that our Jags get very respectable mileage, this 3% loss can be very difficult or impossible to measure on a day to day basis.

-all cars built in the last 10-15 years if not longer used ethanol compatible materials.

- cars since the early '70s were built with sealed fuel systems, so water contamination from the atmosphere is a non-issue.


The number of myths and misconceptions on these points is overwhelming and of course taken advantage of by the snake oil spin masters who have come up with all sorts of cures for nonexistent problems.


BTW 'ethanol' alcohol is the actually the drinking stuff. Same basic process as beer, wine, and distilled spirits.

 

You are indeed correct Mikey, for some reason I was thinking of methanol which isn't the drinking variety. Age I guess? Ethanol is an azeotrope so as you probably know normal distillation will not get you 100% alcohol.
Although car tanks are not the problem the transportation system introduces water before it gets to the car. I remember dipping 1000 ton gasoline tanks for water, sometimes there were several inches at the bottom. I believe we may have some component issues if the US increases the ethanol limit past 10%, but I have no hard data. In general, I think Europe produces higher quality (octane, contaminants, sulphur) petrol than here in the US. This may have something to do with the Summer/Winter switch which the refineries have to contend with in the US.

 

I think given the huge backlash against E15 by consumers, gas station owners and particularly the OEMs through their threats to deny warranty, it's not likely to appear any time soon.

Once again, politics gets in the way of common sense.

 

I found the switch to 10% ethanol very noticeable in mileage. On straight gas the XJ8 was showing 28mpg. The first tank with ethanol dropped the average to 24mpg. To make sure it was the ethanol/gas, checked again with straight gas, and average went back to 28.

Now I can no longer get straight gas...and I never see over 25. So in my experience the 10% ethanol change is consistent and noticeable.

On another note, I remember being taught that lower octane fuel had more BTU's per unit than high octane. Of course, there was no such thing as ethanol mixes back then!

 

i think the fact of the matter boils down to this

car companies dont make any money by telling you to buy the more expensive brand...however they tune their engines to it because it yields better results

so if you're going to spend all that money on a lavish luxury car......wouldnt you want the best results? you have a nice strong V8....would you want it to behave crappy?

and then if it comes down to a money issue....its basically going to cost no more than $5-8 extra per fill up....lets say you fill up every week....8*52 = 416.......if $416 is going to put a dent in your pocket......then maybe a Jag shouldnt be the car you're driving

and im not being rude to the OP....im just speaking outloud because i know a lot of people are in a similar dilemma

 

To CJD and others who may want to use ethanol free gasoline, there is a website available: Ethanol-free gas stations in the U.S. and Canada
I have one about 8 miles from where I live, but the premium gas is 50c a gallon more and in the end I stopped filling up with it. I felt the difference in price per gallon was not worth the gain of 3-5 mpg. Same on my motorcycle and that generally only takes about four gallons to fill up!

 

Na5H- If you noted a difference of 3-5 mpg between E10 and pure gas there was something else going on. Assuming you get around 28 mpg on the highway like most owners, even if the 10% of ethanol in every gallon had NO energy value and just took up space, your mileage could only drop by 10%, or 2.8 mpg. You're reporting almost double that (?)

Ethanol (as much as I think it's political folly and we the consumers are suffering for it) has 70% of the energy of gasoline. E10 therefore has 97% of the engergy of pure gas. On average you would see only a 3% reduction in mileage which is less than 1 mpg loss.

 

John- see my observations above about mileage, same comments.

There's no connection between octane rating and BTU content whatsoever. Gasoline is (and always has been) a complex blend of different compounds and not just one type of dino juice. The end product varies only slightly in BTU content from one refiner to another and high octane can end having the same, more or less than low octane gas.

Again- an octane rating ONLY defines resistance to detonation and NO OTHER parameter.

 

That's a pretty sweeping generalisation.

It is a generalisation that does not bear scrutiny when examined against real experience.

Leading examples on JF are the fuel rail problem experienced by Maxdawg and the fuel pump problems experienced by Reverend Sam and others. One 2007? XK owner is on his seventh dealer installed fuel pump. All of them involved the premature failure of "soft" parts in the fuel system. Those threads can be found with little effort.

The engineers may have tried to account for ethanol in their designs. Unfortunately, thay didn't get it right. It is still a work in progress with owners being the lab rats. Therefore, the generalisation does not apply to most readers of JF with perhaps the exception of the owners of the newest models.

It is a disservice to readers of lesser experience to dismiss the effects of ethanol as a "myth" due to personal bias. This is on the level of proclaiming the Earth is flat and insisting on agreement despite evidence to the contrary.

There is plenty of reading on JF on ethanol, but much more is available elsewhere. Seach terms include "ethanol" combined with "phase separation", "formic acid", "sludge". The search will bring up results from bodies like SAE, API, manufacturers and suppliers to the refining industry.

The evidence is available, so let's stop with claiming that it's all a myth.

 

No .. for a change common sense got in the way of politics. The politics of big oil and big agriculture.

Furthermore, in order for yor statement to be true, there would have to be an advantage to using more ethanol amongst the populace at large. There is not. Octane is not a valid counter argument because ethanol is just one way to achieve the same goal.

 

Companies that supply fluid handling equipment to refiners, fuel transporters, and fuel stations have published technical papers about what you have observed.

 

You should just try out a few tankfuls and see for yourself. Won't cost you much. And you'll know for sure without getting dragged into the quagmire of theory vs. fact vs. myth.

 

Absolutely untrue.

 

What is your justification for this statement. What kind of contaminants are you referring to? They are all filtered the same.