High Octane Gas and the CX7

Ok, I have seen some discussion amongst people about high octane fuel and the CX7. I am turning my 07 lease in on Monday but just got back from the dealership and had this exact conversation with my sales person and a tech about the high octane fuel and people getting hit with lower trade in dollars on the 07's because of this...

I have not ran but the first tank of gas (dealership supplied) with high octane fuel. The 07 called for Premium but with a high mileage commute and limited funds I ran 87 or 89 octane only. I never threw a cel nor had any problems with the vehicle what-so-ever! Even having it plugged in to their computer they could not tell it never ran premium, 23500 miles. The 08 lowered the rating for fuel and "suggested" premium (no change to the motor or compression at all) and now the 09 does not ask for premium at all (no change to the motor or compression). I was told by the tech that the ECU would adapt for the lower octane and run fine. At most you MIGHT notice a slight decrease in power but the average person would not know a difference in performance what-so-ever.

I just wanted to clarify this because several people including the service writer were perplexed as to my not having problems and never running premium. No BS I never ran premium and I have all gas receipts and maintenance records with mileage per tank on each reciept. We averaged 22 MPG and at times saw 26 MPG highway. Once my wife got 28 MPG on a long trip to Northern Michigan. The only mod on the vehicle was a K&N Drop in filter and Synthetic Oil (mobil1).

Moral of the story, dont throw your money away running premium when you dont have to. It is affordable now but wont be in the very near future...

I tried 87 for awhile in my 07 and it was OK UNTIL I got in a situation where I had to really stand on it and boy did the engine rattle until I backed off. I ran 89 after that for awhile and noticed no difference in normal easy driving but, was very aware of the potential for problems. I now just use 91 or 93 and occasional mix it with 1/2 tank of 89. I see no value in risking my engine serious harm to save 15% on my fuel bill.

Well, as Mazda has now backed down on its designation for fuel ratings in the car, 87 octane is fine and there is no change to the motor at all I dont think you were causing problems.

According to Mazda there are several changes between the 07 and 08 CX7 engines. Valve timing, ignition timing, boost control and ECM. Mazda has stated that you will not be able to update the ECM to make an 07 into an 08 so you can safely run 87 octane. Seems that some engines tolerate lower octane fuel better than others or there owners just always drive easer or whatever. I have the latest & greatest ECM & TCM updates and if I run 87 and snap the throttle open fully at certain speed & rpm, I will get violent knocking. Could some engines be higher tuned than others or the ignition and valve timing advance be more aggressive. I don't know.

If he's averaging 22 MPG, I'm willing to bet he never goes more than half throttle.

I'd be curious to if '07s that were manufactured later in the year would have slightly different engine tunings (valve timing, ignition timing, etc.) as they got closer to releasing the '08.

My Vin # is JMER293670164052. I am not sure but, this may be the toward the end of the first buil or start of the second. I'm not sure how to tell. Ed

i just run premium only....why bother taking any risk of running something that is not recommended. Mazda tells you upfront that this vehicle requires it, so why would you not do it, and if you didn't want to premium, why buy the vehicle?

marciano said:

i just run premium only....why bother taking any risk of running something that is not recommended. Mazda tells you upfront that this vehicle requires it, so why would you not do it, and if you didn't want to premium, why buy the vehicle?

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your premise and opinion are sound, very sound in that you would choose not to chance it and you cant really go wrong doing it by the book, BUT a lot of us think it really doesnt harm the vehicle to run 87, and that modern vehicles with computers that are sold allover the world can adjust to octane levels of under 85 to premium and even higher octane race gas. I put 87 in my CX-7 and it runs fine, it runs a bit nicer on 93. if I can buy 93 for around $2/gal I will use it, but if gas goes crazy again, and if its $5-$6 a tank extra to use premium on top of $4/gal I think I will let the cars computer detune so I can ferry my family around on regular. oh, on your point about what mazda says, I have a Harley motorcycle that Harley says I have to use premium gas and 'harley brand' oil... it gets premium when its affordable and brand name synthetic oil. its 8 years old and has been running fine...

**edit** I guess you guys must be talking about 07s? if they really run crappy on 87 maybe thats another story.

AWmustang said:

If he's averaging 22 MPG, I'm willing to bet he never goes more than half throttle.

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Half throttle? hope you arent reffering to me.... I am a lead foot with some serious points on my license. Look at my sig. I dont mess around with my cars. My wife on the other hand is a very average driver. We drive a lot of highway miles as we have easy access to and from work. however, I am not a light foot.

i can definetly see your point chilidogtampa, i agree with what you said. i just got done reading forums about people complaining about buying premium for the vehicle and the fact it does not get 30mpg. i was a little pissy when i wrote that.sorry. How much is gas where you are, I'm in St Louis Missouri and premium here is currently at $1.85

We are about the same for Premium... Regular can be had for around 1.55 if you look for it but averages about 1.61. Makes filling up a lot less painful, that is if you still have a job. LOL...

My only thought on this is that in stock form with premium, the disi knocks like crazy. I've been watching the knock retard since I got my dashhawk about a month ago, and although the ecu is catching most of this, there still has to be a knock detected for the computer to react. I have seen up to 8 degrees of knock retard at times, which indicates a pretty severe instance. Mind you, I've only ever run 93 octane. Hotter burning low octane fuel is not going to help that situation.

I will say that the damage that detonation causes is not going to show up with an ecu scan. What would be most evident would be pitting on the tops of the piston, warped rods or of course catastrophic engine failure (read: piston through the bock).

I'm of couse being a little facetious, but with MS3's blowing for unknown reasons, I am being a bit more careful than I otherwise would be. This car needs to last me 100,000+ miles and I will of course be continuing modifying, so it will be 93 every fill for me. Besides, I spent $25,000 on this car; the extra $3 or $4 a week for my peace of mind is money well spent. IMHO, of course...

Maybe do half tank premium and half 87 but it may not be worth the trouble.
how about them octane boosters? anybody try them with a regular 87 tank of gas?

regiomus said:

Maybe do half tank premium and half 87 but it may not be worth the trouble.
how about them octane boosters? anybody try them with a regular 87 tank of gas?

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octane boosters end up being more expensive than just buying premium.

And around me there is a mid grade option. If i were going to do half regular and half premium, i'd probably just do all mid-grade.

Here is what I don't understand. You have a car payment, insurance, maintenance, all of which cost a fair bit of money. You then go to refuel your vehicle and wish to save $4 on a tank of gas by going with regular instead of premium?

I'm not flaming, I'm just trying to understand the (lack of) logic in this. If $4 a tank bothers a person, I'd imagine a big car payment would be significantly more stressful?