High octane gas

I apologize,

When I first asked about the manual I didn't even catch the fact that I myself was talking about RON.

I fully understand the difference between RON MON and PON.

Sadly I don't understand why I've been getting better milage when using higher grade fuel. Perhaps I need to do more long-term studies where I very carefully calculate my fuel economy over many years rather than just making note of the MPG#s on tanks here and there.

Thanks for a lively discussion.

~Andrew

PS. Hopefully the day will come when we won't need to be talking about cleanest petrol

 

Andrew,

No need to apoligize, this is an information sharing forum, without someone to ask the tough questions, it would be pretty quiet around here! Please do keep us up to date as to what your research uncovers.

Calculating long term mileage while testing different products/techniques on just one car is extremely difficult to do. There are so many factors to take into account that some people argue that its impossible.

As for me, I just continue to test because some data under whatever humble testing I can do is better than no data at all.

What you may have experienced is that something else changed that you didn't notice (warmer temperatures, engine is breaking in and is a bit looser, different engine oil, different driving technique, etc.)

Please keep us apprised of what you find so we can add your data to ours.

Enjoy,
Bob

 

Well one possibility is that light-footed driving is the cause of my belief that higher octane fuel leads to better fuel economy.

I've always calculated my annual gas milage and found that it is much higher than other people I know who do the same thing.

Perhaps it's just because I tend to drive like a grandmother.
I'll try to keep everyone updated on things.

~Andrew

 

i'd like to take exception to that part, Gen2.... i've used Rotten Robbie's gas whenever possible since i moved here in '78, and never, never, never had any engine problems that could be attributed to bad or poor gas. i HAVE heard some stories of the origin of the brand, and their sourcing of fuels, and that underscored my lack of worry.

i'd put those rumors in the class of urban folklore, imho.

oh, i did have a clogged fuel filter in my '82 Isuzu Diesel, where all but about ten tanksfull came from Rotten Robbie's on Stevens Creek near Tantau, but that clog came after about 50,000 miles or so of not changing the filter. the dealer didn't even recognize the symptoms, and rebuilt the injector pump twice (on their nickel) before figuring it out....

 

a few more comments on preignition, "knock", octan

high octane gasoline does burn slower. i have some doubts that it burns slower enough to influence the level of unburnt hydrocarbons that go out the exhaust valve for the catalytic converter to handle. even if that were the case, wouldn't the O2 sensor upstream of the cat cause the ICE control module to cut back on the fuel input, anyway? the catalytic converter is THERE to burn off unburnt hydrocarbons anyway, and if it overheated from use of premium fuel, wouldn't an indicator light go on? has anyone reported a warning light from that?

next, high octane fuel in older, carbureted and Kettering-ignitioned engines allowed the spark timing to be advanced more than for regular fuel. this allowed the spark to get the fire in the combustion chamber lit further before Top Dead Center was reached by the piston, so that, by the time most of the fuel had been burned, heated the air in the combustion chamber, and started to push down on the piston top, the crankshaft would not have turned so far, and the piston gone down so far, as to waste so much of the energy in the fuel! if you used low octane fuel in a high-compression engine, the fuel would be lit too far before TDC and could actually start pushing the piston down before it reached TDC! total waste of power, fuel, etc.

THEN came knock sensors: basically little microphones bolted to the intake manifold. they "listened" for the pinging of preignition, and fed their signal to the engine control module, which would, on the fly and in real time, retard the spark enough to bring the pinging intensity down to a level which would not damage the engine. putting premium fuel into a car with a knock sensor might get better gas mileage, because the control module could crank in a few more degrees of spark advance, and THAT could kick up the horsepower, too.

part of the problem of fuel burning quickly in a carbureted engine could be overcome by redesigning the carburetor itself to provide better atomization of the fuel: smaller droplets. the Rochester Quadrajet, for example, had three venturis in the primary throats, stacked one above the other, for better atomization of the fuel. note, i say atomization, not vaporization. if the fuel could be vaporized completely, that would be the optimum, but no commercially successful carburetor could do that. see historical notes on the Pogue Carburetor and the report many years back in Car and Driver on the "Dresserator", which pretty well pulverized the droplets by creating sonic shock waves that smashed the droplets before they even left the bottom of the unit!

finally, pinging, preignition, and all that stuff isn't caused by gasoline being absorbed into carbon deposits in the cylinder head. what happens is that the carbon deposits build up (and in the old days actually could raise the compression ratio of the engine, FORCING you to NEED higher octane fuel!) and collect HEAT from combustion, not fuel, per se. when the incoming fuel mixture gets compressed, and thus heated, by the rising piston, if it contacts a hot enough piece of that carbon deposit, the heat from the carbon will ignite the fuel combustion before the spark plug goes off. in this way, the timing of that combustion is totally out of control of the ignition, and performance goes down the tubes.

in extreme cases, preignition like that can start so early that the piston rises against a shock wave of burning fuel, and that's called detonation, and that's the thing that can burn holes right through pistons if it's bad enough and goes on for too long (too many miles). in Diesels, it's also referred to as "nailing", and once i heard a Mercedes Diesel on local interstate 280 nailing so loudly that i could hear it in my car at 55+ mph! that engine was doomed, and there was nothing i do to tell the owner.

end of rant.
thanks!
cheers!

 

Re: a few more comments on preignition, "knock", o

You are in a catch22 - If you cut back on the amount of fuel, you still don't get a guarantee of complete combustion, but you have less energy available, which means less power - one of the known issues with using High Octane in engines tuned for Low Octane.

The Indicator Light isn't from overheating, it's from detection of excess emissions, and yes, it's been reported on Classics, and Toyota explicitly mentions it as a possible effect of burning High Octane fuel. I'll try to find the reference.

Remember, one of the reasons the CARB states have a longer emissions warrantee is cleaner fuel.

Stands to reason to me that dumping crap into the emissions system unnecessarily would not be good for the part longevity, greater pollution notwithstanding.

Part of the reason I got the car was to decrease pollution.

And remember, Lower Octane burns HOTTER than High Octane. Thus bringing the emissions components up to temp faster, decreasing the amount of time the engine has to run just to 'prime the pump' and maintain temp in stop and go traffic.

Doing something that costs me more, lowers my mileage, lowers my available power, and can possibly harm my car and the enviornment just doesn't seem like the logical choice to me.

 

I find it funny (in a sad sort of way) that we are bickering over miniscule variances in amounts of emissions in some of the most advanced emissions-controlled cars on the market...
While at the same time there are people out there putting number 2 heating oil into their diesel trucks, and individuals who never change their oil, clean their motors, or run injector cleaners through their tanks. There are people out there who only get about ten or less MPGs, and here we are arguing over such a tiny issue.

:lol:

 

I understand that there are many people that use entry level gas like Rotten Robbie (they aren't the only entry level gas, just the one with the most complaints and significant press at the time of our test).

What I was trying to get across was the experience of a large group of people that owned high strung cars, not that any one person was doing anything good or bad.

Our theory was that we would be more sensitive to variations in gas quality and would thus be able to be selective about which gas we use. After all, if someone doen't want to be selective, they don't have to be, but its nice for them to be able to read about others experience should they encounter a problem.

Once we determined what gas gave us problems (in the other cluib), it turns out that we all also wound up avoiding using these brands for our regular everyday cars. In every reported case, all instances of suspected gas related problems went away completely.

This was hardly a scientific test but since we probably accumulated several hundred thousand test miles per year, we figured that our ad hoc test was better than no scientific test at all. The members that had been using entry level gas stations also had a high correlation of using fuel system cleaners or occasionally changing to a premium brand for a short while.

This is no different than us in PriusChat reporting ourimpressive fuel economy every month and there also being a thread in the forum by members that can't break out of the 40s. They need to speak out their issues even though they probably feel that they are in the minority.

Back to our gas brand test, it turned out that running a bottle of Techron fuel system cleaner regularly did help things out. Unfortunately, regular use of it was more expensive than running a premium grade gas all the time so they eventually changed to just using Chevron and stopped experiencing problems.

I admit that they probably could have changed to some other premium brand and have had similar results but Chevron just worked so well for so many of their race cars that everyone just naturally gravitated towards it for their street cars.

Some of our members were also involved in the lawsuit against Rotten Robbie (fuel system damage due to non-disclosure of the high amount of alcohol that was blended in their gas). This certainly has given that company a black eye that I assume contiunes to this day. (Do they now clearly disclose how much alcohol by percentage is in their gas?)

If you choose to use entry level gas and it works well for you in the long term then good for you, as you no doubt have saved some money compared to me.

 

Re: a few more comments on preignition, "knock", o

The contamination of emissions systems due to using excessively high octane is a known effect, not hearsay. For starters, please read all the links that I posted earlier in this thread. If that is insufficient then maybe one of us will find the Toyota statement as such. (I have also read this Toyota statement, but I can't remember where it was.)

 

I agree with you but I am also sensitive to not adding to the pollution problem by avoiding the almost complete failure of my emissions system's performance over enough time through the continued use of excessively high (premium) gas.

I prefer to think that we are polishing the state of the art by critical analysis and thus pushing forward our performance to the Nth degree. Maybe we are trying to set a better example to those that inappropriately burn #2, or maybe we just dig learning more?

In the computer field we have an example where critical inspection of every line of software code has led to a more secure operating system (OpenBSD vs any opther version of BSD UNIX). Maybe there is a subconcious part of us that is driven to make things better?

 

Re: a few more comments on preignition, "knock", o

It is true that the cat is there to get a second chance to catch those pesky hydrocarbon escapees, however there is a limit and Toyota itself warns against this.

As has already been posted, there are already incidents with owners experiencing warning lights on our cars and others. What struck me as I was reading your post was that waiting for a warning light is sort of like waiting to have a major heart attack before considering preventive measures. Sure you might survive the heart attack to change your mind, but its an expensive and potentially fatal gamble.