Gasoline Grades
 

Before you all jump all over me: Yes, I did a search and did not find a thread answering my question.

SoOOoOoOoo....

I know the car manual and the sticker on the gas door says 'Premium Fuel Recommended' but has anyone tried either a mid-grade or *gasp* regular grade?

I know this will open up the discussion about octane and the such...but does anyone here run something other than premium and if so, have you noticed any bad effects?

I haven't personally, but I've heard lots of stories of people trying lesser grade gas without adverse effects. The manual says you can do that, but you'll sacrifice some performance. I haven't heard stories of mileage using lower grade, but I'd expect a marginal decline there.

I bought my car on 04/15/04 after I sent Uncle Sam his check.
My first fillup I got 164 miles and 7.8 Gals = 21mpg
Filled with Premium Amoco/BP.
Second Fillup 212 miles and 10.95 gals = 19.4mpg
Filled with Amoco regular(due to gas price)
Third fillup 231 miles and 11.1 = 20.8mpg.
Filled with Shell Premium
Fourth fillup 142 mile and 7.45 gals = 19.06
Filled with shell regular
Fifth fillup 122 miles and 5.8 gals = 21.03mpg
Filled with shell regular
Sixth fillup 178 miles and 8.6gals = 20.7

So far basic evidence shows me that I am getting better mileage
with regular than premium. I now have 1200 miles on the car and
I know that I do not have the L or M flash. Matt Davis the sales guy at Trussville Mazda lied to me about this. I ask before I bought the car. It doesn't sweep on the stomp test.
Otherwise I love it.

katchoo you might want to read this thread started just today asking the same question.

There are a lot of threads on the subject. You'll have to change your search terms.

I have been using Shell 87 almost exclusively for over 7000 miles. I'm getting typically 18-19 around town, 23-24 on the highway, all with plenty of zoom-zoom, and no detonation or performance degradation that I can sense. But, then again, I don't drag race it...

I switched to 87 octane. Runs just fine. No problem with performance.

A lot of dealers will tell you a car needs premium gasoline just to make you feel like you drive a "premium" car. But I would definitely like to see some definitive data on this. Those extra few cents per gallon = more money spent on the car itself.

The term I used was 'gasoline' - a rather broad sweep. I just didn't see a thread that answered my question. I wish people would label their threads better...

Anyway, it seems that most folks have not had a problem running the lower grades. I will try it next tankful.

My Probe GT said use premium also, but I never did and it always ran fine.

I was concerned more about damaging the engine rather than performance.

Thanks for all your responses!

Try this thread. Should tell you all you want to know about Octane.

I have been using regular for a couple of months. Performance could be lower, but I can't tell the difference. Mileage has stayed the same at 19 in mixed driving. I would not have tried it, except the manual says it is OK.

From what I read, lower octane gas actually have more stored energy per volume than higher octane gas. So the general recommendation is to use the lowest octane gas that doesn't cause detonation.

I've even done several of my own (unscientific) tests in my old I4 Accord. All I remember from them is that my MPG actually went down with no perceptible change in power (butt dyno!) with the higher octane gas. I'm sure that'll be the same with my new I4 Accord.

The one rumor that I've found interesting is that the Accord's V6 will output 240 HP on 87 octane, but will output 250 HP on 93 octane. This is according (no pun intended!) to Honda's engineers, but I haven't done a whole lot of research on this as I wasn't too interested in the V6 at the time. Alot of people claimed that this is true according to their "butt dyno", but it might just be a placebo effect. They do say that it takes several tankfuls as it take a while for the computer systems to detect the change in the octane. I wonder if the Renesis engine is similar. Especially since one person in the other thread mentioned that the first tankfull of 87 octane gas had lower MPG, but the subsequent tanks got better MPG than when he was using premium gas.

The Accord's I4 has a 9.7:1 compression and the V6 has a 10:1 compression.

Someone needs to do some dyno runs or Gtech runs on both regular and premium with the same outside condition, and the same gas level in the car to see what happens.

That's a really good thread.. albeit really long.

Quick question... The manual states using a grade with less than 91 octane results in reduced performance. Does that have any affect to longevity of the engine?

While I know that premature detonation in the engine can reduce the engines effectiveness... does it actually hurt the engine?

Sorry if that's a stupid question... but when it comes to cars, I claim stupidity.

Thanks.

I tryed 4 tankfuls of Citgo Reg. I think in ran OK and even gave slighty better mileage. You can run it if you want. The high test will make it run a lot smoother. I am back to prem now. I still have the C patch est. My dealer believes you must get a check engine light to get a patch. He just might get a lawsuit instead.

I think that the issue is that lower grades theoretically might cause the computer to adjust the ignition timing to prevent detonation with a net loss of power. In other words, you don't notice engine knock with lower grade gas, but you lose power.

I have tried all grades and have discerned no great change in power nor in mileage. I have kept careful records and my best mileage has consistently been recorded with mid-grade 89 gas. 87 and 93 seem to be the same and close enough to the 89 that I can't tell is the effect is real or not.

There have been many threads on this subject and the overwhelming consensus seems to be that 87 works fine.

Right..

So it's basically "wait and see". "Do it if you feel comfortable with it." I understand that.

From what I gather...
10:1 compression + lower octane = higher temperature than expected
higher temperature = possible premature combustion?
premature combustion = engine wear?

Is that a reasonable assessment? I'd love to jump on the 87-grade bandwagon.... but really worried about the long term risk.

What does theory say about that?