Bobo

I consider you to be one of the most knowledgeable members who contributes to this forum, but others with any degree of knowledge are relatively scarce. Bill has contributed greatly to the stickies in this forum, but apart from that his whereabouts remains a mystery to me as I never see him weigh in on anything.

SilverMax_04

Thanks for the compliment. I try my best. And luckily for us all, I have a friend who knows even more about octane than I do. So when I run into something I'm not certain about, I contact him for the best possible answer.

Every so often Bill will provide a comment on lube questions, but you are correct that he does not reply very often. I suspect he feels his stickies answer most questions, if people would not ask and simply look for the answer there.

alpimax99

iTrader: (2)

anything under 93 my car runs like total crap i can really feel a difference when i buy cheap gas

SilverMax_04

You did not say how many miles on your Max. Your spark advance adjustment may not be working properly. Or you have substantial engine deposits that boost the Max's octane requirement above where the spark advance can control at anything less than 93 octane.

You can check both of these to see if there are any problems, or continue to buy only 93 octane. I would start assuming the deposits and try a bottle of Techron in your gas tank.

jipi

you guys all have it good. super has reached highs of 3.03 here in ny.

Bobo

That's peanuts compared to what it is even across the border in Canada and we send you the frigging oil.

SilverMax_04

If I'm not mistaken, Canada has a much higher tax on gasoline than the US including most state taxs.

Also, it is not so much the actual cost of crude oil, although it is high. The speculators are running up the cost of incremental crude oil in the NY commodities market (to higher than most contract crude sells for).

The other problem is a shortage of refining capacity in the USA. It has been over 30 years since a new refinery was built in the US (don't know about Canada), while at the same time many smaller inefficient refineries have closed.

So in the US you have high incremental crude costs and a shortage of refining capacity both pushing the cost of gasoline (and diesel fuel) up. My advice, wait until after Labor Day and gasoline prices should come down some.

Bobo

I also believe the cost of gasoline will come down after Labor Day. The next shoe to fall will be incrementally higher natural gas and heating oil costs, particularly in the US Northeast, this winter. Be prepared to wear your winter clothing indoors, lol!

dr-rjp

iTrader: (4)

Ditto on the "engine runs like crap on 89 octane." It runs OK on 91 octane, though. However, anything less produces a noticable difference. When I changed my plugs, the plugs looked clean, and when I shined a light through the openings, I did not see any carbon deposits.

My timing is advanced 15 degrees. Is that too much? I've got 120k on the car. I do suspect that it is running a little rich, maybe I need an oxygen sensor replaced.

One thing I noticed with some brands like Shell, that their lower grades smell a lot harsher than premium. Any clue why that is?

SilverMax_04

You say it does not run as well on lower octane, but you don't mention light engine knock. Suspect you may be just short of having that, but less than full performance. In this event stick with 91 octane. If you are running slightly rich, that fact will tend to reduce your engine's octane requirements. The evaporation of the extra fuel cools the engine which reduces the engine's octane requirement.

That timing may be advanced too far. Don't know what Nissan specs call for with your Max. In my Max the spark advance is controlled by the car's computer.

There may be deposits on the valve face, but most engine knock starts at the plug before the plug fires, so that is probably not your problem.

Not surprised by the smell of regular. There are many compontents that are blended to make gasoline. The lower octane components generally don't smell as good as the higher octane (this does not apply to all components and is just a generalization). In the old days before mandated lead-free gasoline, the components in regular tended to have more sulfur content than in premium. There may still be some of that (more sulfur in regular), but the mandated sulfur content on all current gasoline is substantiall below what was common in the old days.

Even lower mandated gasoline sulfur levels are supposed to be coming in the future. Lost track of when this takes effect.

McNasty360

Where I live gas is up to 2.99 a gallon, but i still use premium.

carnal_c30

iTrader: (38)

eh ****... if you're trying to start shlt with me take it to PMs... if you're trying to be cute then shut the fock up.... and old guy like you should have better things than to try to start mess on an internet forums... go raise your kids and work harder at your job... if you have one

my reason for my use of 100 octane is to prevent detonation, my car isnt running so well so it was a temporary fix... no biggie as I got a couple other cars to drive... so dont call me stupid before you know wtf you're talking about

and if you gotta say something else like you dont like my sig then say it straight up, only bltches play games like you

Bobo

You suggested before that you had a problem and I simply agreed with you. I have nothing more to add.

carnal_c30

iTrader: (38)

ok : lol

dr-rjp

iTrader: (4)

What does that have to do with your imbecilic remark to me about specific density -- which was answered eloquently by SilverMax, who does a lot more for this board than to simply run his mouth like you do.

As for determining fuel economy, I guarantee that I used a much more controlled situation in measuring my 158 miles than anyone else.

For example, has anyone bothered to make corrections for their speedometer being off at highway speeds? I have yet to find a stock speedometer that is 100% accurate at highway speeds.

Secondly, do people begin and end the test under the same environmental conditions? Do they run the test when the ambient temperature is coolest or highest?

Third, do people let their tires warm up to their maximum temperatures before running their test, or start the test off with their tires cool?

Fourth, do they fill it up to the filler tube, or until the pump shuts off?

If my 158 mile test has any measurement error, I would estimate that it is less than +/- 1 mpg.

SilverMax, your opinion on measurement error, please?

Bobo

And I thought I was ****. My approach is much less scientific. I just fill er to the brim, go on a road trip, when the light has been on for awhile, say at 500 to 550 miles on the trip odometer, I fill it to the brim again. It works for me.

What has your approach taught you?

SilverMax_04

Thanks for your conficence. I try hard and have an SAE friend I can consult when needed.

As to measurement error (I assume in calculating MPG). I have noticed that just about every gas station pump will shut off with a somewhat different level in your fuel tank. There is no help for this, it is the variety we see in our everday world. When filling my tank, I like to fill it past where the auto shut-off cuts the flow off the first time. I can listen to the fuel (when the tank is nearly full) flowing into the tank, down the filler neck to the tank. When that sound changes, I feel the tank is full. I believe this gives me a more accurate measure (rather than use first shut-off every time) from tank to tank of how much gasoline has been burned.

When my 04 was new, I compared the calcualtion using the gasoline into the tank with what the Max's computer said was my mileage (in MPG). I understand the computer has the ability to measure the flow of fuel into the engine, so that number should be very good. I found that the two numbers were quite close. So, while I continue to keep gasoline purchase records (and can go back an do all of the calculations), I tend to believe the computer calculated numbers as being at least as accurate as my manually calculated MPG figures.

dr-rjp

iTrader: (4)

Thank you for asking. I found variations in the areas mentioned:

I get better mileage in the morning when the temperature is 75 than in the late afternoon when the temperature is in the upper 90's.

I get better mileage when my tires have been driven awhile as opposed to starting with them cold.

I get better mileage at a constant 50 mph than at 70mph.

When my speedometer reads 80mph, I am actually going 77mph, so I have to multiply my mpg results by 77/80.

I get more accurate mileage estimates when I fill the tank up to the brim, and when I fill it first thing in the morning when the car is still cold.

And, believe it or not, I get slightly better mileage on Chevron than on other brands...including BP and Shell. Must be the Techron.

Up until my highway trip, I had only been calculating city mileage by using one tankful plus 10 gallons to reduce error caused by variations in filling and by having a bigger numerator.

BTW, I didn't intend on only going 158 miles for my highway test, but the distance was dictated by the reason for the travel. If I could have gone 450 miles, I would have. Since my company pays for business trips, I rent a car, so I do not have many opportunities for highway drives.

Bobo

Aha, your last paragraph explains it all to me because I was questioning the validity of the results of a 158 mile road trip. But if that is what constitutes a road trip so be it.

I take it you may not have winter gas in Florida which I find reduces my fuel economy by as much as 10%, although colder startups and longer to operating temp in colder weather may account for some of that. Hopefully switching to Esso XD3, 0W30, full sythetic from dino juice following my AutoRX clean and rinse will offset that to some extent.

dr-rjp

iTrader: (4)

How does winter gas differ from normal gas? And, what is AutoRX? Any better than Seafoam?

dr-rjp

iTrader: (4)

I was wondering if our cars could stand a mix of gas and ethanol without any mods or ill effects if the percentage of ethanol is low?

SilverMax_04

All new cars (since about 95 or so) are designed to handle up to 10% ethanol in the gasoline. You should have no problems -- unless you have a lot of water in the bottom of your tank and have never used ethanol in gasoline before. The ethanol combines with the water and it all goes through your engine. A little is not problem, a lot can be. Also remember that gasoline with 10% ethanol has about 6% less energy than gasoline without. So your actual mileage will suffer, although you may not notice that small of a loss in mileage.

Winter gasoline is blended so that it evaporates faster than summer gasoline. If it did not, it would be much harder to start your engine on a cold day (below about 20 degrees F). The Fed Govt regulates how volitile winter gasoline can be to control evap emissions from vehicles. But it still evaporates faster than summer gasoline. Most oil companies add some butane to the gasoline to increase its ability to evaporate in the cold.

Bobo

AutoRX is more effective for cleaning ring packs, crankcases and engine internals than Seafoam. I haven't used Seafoam but would consider using it through the brake booster cable to clean out the intake manifold, which is not the role of the AutoRx. A lot of members of bobistheoilguy.com swear by AutoRX. See www.auto-rx.com

There is also a product called LubeControl (LC for the crankcase and FP for the gas tank that is garnering a lot of kudos. See www.lubecontrol.com

spoon787

About using cheaper gas to save money. If you just think about it, no matter what the price of gas is, premium is only 20 cents higher than regular. I dont let my tank get below 1/4 tank. it usually takes around 10-13 gallons to fill. thats only 2.00-2.30 more to fill up. in fact if you could actually take the enitre 20 gallons it would only be 4 dollars more per tank. neglagable in my opinion. plus the higer octane gets better milage. this formula works no matter how high the price of gas gets, because they regular is usually 20 cents cheaper no matter what.

JwaxMax99

iTrader: (14)

SilverMax....does premium really produce better mileage like this guy claims? Is their solid data to back this?

SilverMax_04

Accurate Answer: It depends on the specific engine and your driving habits. For cars specifically designed to burn regular, premium will make no difference. For cars designed to run on premium, but capable of burning regular there may be improved mileage. What I think most of us want to know is: Will premium in my Max improve my mileage?

I maintain that for driving around town there are simply too many factors in play to get reasonable numbers on this question. Driving the expressways removes many (but not all) of those variables.

I did a small test this summer on my almost 5k mile trip using premium for a segment of that trip. The numbers seem to indicate a slight improvement in mileage, but the cost per mile for premium vs regular was essentially the same. In other words, the higher cost for premium was almost exactly "paid for" by the slightly better mileage. This small test indicates that I need a "better answer" to this question. Previous to this, I've always assumed that regular was the most economic choice (cost per mile) for my Max.

This December I will be driving to and from Chicago. I plan to do an even more extensive test on that trip. I will burn the cheapest fuel on the trip east -- in Nebraska and Iowa that is mid-grade made with 10% ethanol -- which has 6% less energy than gasoline without ethanol. On the trip West I will fill up in eastern Iowa with premium in an almost empty tank and burn premium for the entire trip home. I will record the wind direction and its approximate strength for each segment between fill-ups. I'm hoping that this test will indicate to me whether the higher cost (20 cents per gallon) is more than paid for by better mileage. I will report the results of this more extensive test on a new thread on this site when I get back in early January.

dr-rjp

iTrader: (4)

I have been mixing roughly equal parts of 89 and 93 octane to get a yield of 91 octane. Car drives just fine on this mix, plus I am actually getting slightly better gas mileage than running straight 93 octane.

I did not believe it at first, but after three tankfuls, I do now. Best city mileage I had ever gotten on 93 octane was 19.3mpg. After three tankfuls on the 91 mix, my best mpg was 20.8 and a three tankful average of 19.7mpg. This includes carrying around three passengers over the long Labor Day weekend and a few, jack-rabbit starts.

Could it be because running on 91 backed the timing off a few degrees fom its 15 degree advance??

SilverMax_04

I still maintain that there are too many variables trying to compare mileage while driving around town. Slightly cooler temps alone could have caused the 0.4 mpg average improvement you saw -- or how you filled your tank on each fill-up.

But the real test of whether paying more for higher octane is worth doing is not a better mpg on premium, but a better cost per mile driven for the higher cost gasoline.

In your case, buying cheaper mid-grade and getting a better mpg average is obviously more economic than burning pure premium.

dr-rjp

iTrader: (4)

Well, that was the substance of my post ("RE: Calculating city mileage is a big waste of time"), so I agree with you.

On the other hand, I am comparing myself to myself, rather than to anyone else, so we have a case-controlled study here. The weather here has been about as constant as it gets, and my mileage is constant as well in terms of when and where I drive; e.g. about 80% of it is back and forth to work.

With gas prices the way they are, my driving goals have changed from running redlight grand prixs to one of maximizing fuel economy.

This goal is expecially important for the very constancy in my travelling; i.e., there are no other options for going back and forth to work except via my car.

I was hoping that this thread would begin to turn in that direction; i.e, how to get the most out of a gallon, rather than continuing on as a p***ing contest where the distance travelled is not the car but the claim.

Maybe it is time to begin a new thread that would invite members to share new mileage tricks, or at least, ones we haven't heard a gazillion times.

Thoughts?

SilverMax_04

This is a thread about Octane and not about Improving Gasoline Mileage. So a new thread would be the best option.

A simple example of what I'm talking about cost per mile and cost per gallon calculations.

Assume that you can buy regular gasoline (87 octane) at $2.00 per gallon (don't I wish) and premium gasoline (93 octane) at $2.20 per gallon. Also assume that your Maxima will run somewhat better burning premium but will operate adequately burning regular (this describes my Max).

If your Max get 22 mpg burning premium your gasoline cost per mile is 10 cents. If you Max only gets 20 mpg burning regular, your cost per mile is still only 10 cents. If you get better than 20 mpg bruning regular, it becomes a better buy than premium. If you get less than 20 mpg burning regular, them premium is a better buy for your Max.

The simple calculation for each grade is cost per gallon divided by miles per gallon: cents per gallon / miles per gallon = cents per mile.

dr-rjp

iTrader: (4)

In keeping with your cost per gallon concept, I would also include other costs (repair and maintenance costs) that may arise from using gasoline with a lower octane rating than what is recommended by the manufacturer.

Are there any research to show what, if any, are the long-term effects (three or more years)?

I've read some anecdotal claims here and there, but what I want to find is some hard evidence.

SilverMax_04

For my 04 Maxima, Nissan recommends premium for maximum performance. (I take that to mean on the track or at a dyno test. Since I do neither, I don't normally burn premium.) They also say that the car will perform adaquately on regular. I have 38 K miles (and about 2.5 years -- bought Max in May of 03) on my 04 normally burning regular. (In Iowa and Nebraska I burn mid-grade because it is cheaper than regular.) I have no expenses to date from burning the cheapest grade of gasoline. So what should I add to the cost per mile calculation for bruning regular? Should I just assume some cost that I have not paid, yet? Based on Nissan's recommendations, I don't think there will be any added maintenance cost from burning regular. Time will tell.

dr-rjp

iTrader: (4)

I find it hard to believe that Nissan would equate "Maximum performance" with a dyno or a track for a car marketed to be driven on American roadways under normal driving conditions. To me, "Maximum performance" means better acceleration, better starting, better gas mileage, and less reliance on sensors and computers to compensate for low octane gas.

When you think about it, we put an awful lot of reliance on these sometimes flaky electronics to bail us out if our cars start to knock. Knocking is not something that can immediately make itself known unless one actually listens to his or her engine every time. If the AC is running and the stereo is playing, well, then, good luck hearing anything.

Now, better acceleration may not be a big deal to some, but for me, having that extra power can mean the difference between avoiding an accident, or getting into one.

If Nissan recommends 91, then they want you to use 91 if it is available. If it is not available, then they say that 87 can be used. For how long can it be used?

Aye, there's the rub.

Maybe, the manual should read, "If you cannot afford to use 91 octane, then how could you afford to spend 30K on our car?"

SilverMax_04

We can agree to disagree on this topic. I find that my Max gives me quite good acceleration burning regular. I had a rental car for 8 days when the Max was getting body work done -- now that was a dog as far as performance.

If I were going to race someone, I would want premium in the tank for the extra bit of performance. Since I don't, I don't.

RandyZ

I use regular so far and am happy.

SilverMax_04

Good for you, Randy. I suggest you find out a little more about octane. Remember both of us are burning regular in an engine with a 10.3 to 1 compression ratio. The VQ is a very sophistocated engine, but you should know more about what causes engine knock. Suggest you go to my earlier thread on this site and read about what operating factors cause engine knock -- here:
http://forums.maxima.org/showthread....6&page=1&pp=30

You will find there the 3 major factors that you need to watch out for to be certain you don't get engine knock.

dr-rjp

iTrader: (4)

About your suggestion to add Techron to your gas tank to clean out deposits, do you happen to know what, if any, differences are there in the amount of Techron added to premium Chevron versus regular Chevron?

SilverMax_04

In the mid 90's most oil companies put a higher dose of fuel injector cleaner in their premium than in their regular. With the very competitive gasoline market in the late 90's and after 2000, many cut their treatment rate in all grades to the government mandated minimum. Now some oil companies are still claiming to be putting a higher treat rate in premium. I can not be certain if Chevron still does this, but there is a good chance. You might check their web site to see if they make this claim.

junzhang

The price difference is $0.2 between 93 and 87. With sky rock gas price, the relative is less and less. With more high octane and better more detergent, Get 93 or maybe mix 93 and 87 to get the best performance and peace of mind. If oneday gas price base price become $5.99, I'll turbo all my car and switch to Oct93.

dr-rjp

iTrader: (4)

Taking a page from SilverMax, I filled up with 87 octane BP...right before the prices shot up due to Rita, I might add.

Here's my subjective appraisal of how the car is reacting, so far:

First of all, there is no knock or ping...which is a good thing.

In fact, the idle is exactly the same...maybe a tad smoother.

Where I notice the difference is in acceleration and shift timing. First of all, the acceleration is a lot slower: it feels like I'm towing something or if I've got a carload of passengers instead of just me. The sound of the acceleration (engine & exhaust) is also different: it is more muffled than before.

Next, downshifting from 1st to 2nd produces more hesitation, shudder or "shift shock" than before. Upshifting is not affected at all, even with the decline in acceleration.

It will be interesting to see what happens to my gas mileage. I predict that my gas mileage will probably increase -- not from the adjusted engine timing, but from being less inclined to punch the accelerator to pass other cars.

Bottom line: I probably could learn to live with the change, if I had to do so. What's more likely is that I'm not going to use anything less than midgrade again. It's worth the extra $2 per fillup.