rx8cited

Me three :D, but I'd like to drive it for one tankful.

aggietiff28

Honestly...whatever is closest when the gas light comes on...or cheapest (note: I won't use HEB, Walmart, or no name brands). I will agree with you that Shell is the best that I have used...I am just not that picky since the 8 is greatly increasing the cash flow OUT of my pockets. I have been wondering about the "pinging" that people describe. Maybe I just got a really good 8 or maybe it really does take about 15,000 - 20,000 miles to completely break in the engine.

slllygrl10

I use Premium and well known brand. Such as shell, chevron etc

romulus

Just an observation that I noticed on my car. I may get flamed, but I thought that it would be interesting. My car has 16.4K and I have been getting 19 to 19.6 MPG. Usually I fill up my tank with 91 octane after 240 miles; about a notch or so lower of 1/4 tank mark in the gauge. I do about 80% freeway @ 70 mph and half of the distance with traffic ~30 mph with stop and go in some areas.
Now here is the interesting thing. I normally use 76 gas station and it gives me the mentioned fuel economy. One time I decided to go to Costco and fil up with 91 because I was running low; and besides I was already there anyways to do some shopping. I noticed that my MPG went up to 20.7 MPG. That is strange, so I decided to try it out a few more tanks (5 - 7 ) and indeed my MPG is about that. One time I got close to 22 MPG, and my driving habits has not change nor my route or the traffic. I simply use my car to go to work and back home with a few miles in between for small errants. When I switch back to known brand gas, regardless if is 76, mobil, chevron, etc. My MPG goes back to 19 to 19.6. By the way I keep a close log book about my fuel economy since I got my car. I know that costco gas is not the greatest thing but so far I haven't experience any engine pinging when I do a WOT.
Anyone have experienced the same?

Maolin34

I spoke to a Mazda Engineer today....I will make a new post with what was said, but part of it fits in this post...

It has been mentioned before, but the engineer confirmed it for me...using full with as little ethanol or any "nol" for that matter will make a measurable difference. I am not sure of the contents or additives used in different areas of the US or world for that matter...but for my area (Michigan) he recommended Sunoco Ultra 94. Typical premium octane is 92 in Michigan.

If you want to know more about what I found out...check my post in the RX-8 Discussions area.

czr

iTrader: (3)

I went from Hess (convenient) to Shell both mid grade and mpg jumped up over 1 mpg. For you looks like Costco jumped you up a little over 1 again. That Costco note was surprising and I'm tempted to try them out. But gas mileage aside, is their gas any better/worse for the car? It's definately cheaper but..

romulus

I remember back in May-June timeframe that there was a discussion regarding the quality of gas from the known brand and the "generic" ones. Based on what I remember that all the gasoline in your area are made in the same local refinery if any nearby. The tankers trucks pulls out from the refinery with the same "basic" gasoline. then they go to their company's formulation station to add their "additives" I am not sure what additives have the gas from costco or other small gas stations. At least I know that they are using the right additives to make 87, 91, etc. octane. My guess that the generic gas does not contain not much detergents like the brand names. But, for me I usually commute 60 miles per day and normally I fill up on Thusday night If I start my commute on Monday with a full tank. With Costco gas I can push it to 280 miles with 1/8 tank left and no low fuel light. And about 13.4 gallons pumped. I am planning to alternate the fuel brands so at least my baby gets all the cleaning additives.

quack_p

I read through a bunch of gas threads a while back, and several members swore by Shell V-Power. So that's what I always use.

Limey

In the US, 87, 89, 93 are the general three Octane levels available. I know in the UK, 95 is the lowest! So, my questions is, are the engines made different for the two countires.
I am from the UK but drive my 8 here in Alabama, US. I use 93 but have tried the 89 level a few times. I have noticed a reduction in performance, especially obove 6ooorpm. Due to this I have never even tried to use the 87 Octane. A reduction in performance I can handle at times, but engine damage, I cannot!

Rick

Doesn't the manual also say that using a lower octane fuel can result in a loss in performance? Correct me if I'm wrong but isn't the loss in performance caused by the timing being retarded because the knock sensor has detected knock which in turn is a bad thing for the engine? (gasp for air)

rodmeister

I was skeptical about Shell, but tried it and my car seems to run smoother and with a bit more pep. Costco gas was hit and miss, sometimes my car ran smoothly on a tankful, other times I'd immediately feel a roughness.

rx8cited

Different engines are not required. In the US octane in computed using the (R+M)/2 method or (RON+MON)/2 in other countries such as the UK, they use compute using RON which calculates to a higher number for the same fuel.

For example, if you look in the owner's manual, they recommend fuel with octane 91 [ (R+M)/2 method] or above (96 RON or above) ..... so US 91 octane is UK 96 octane.

Limey

Thanks for tech info. Bottom line is I do not want to do damage and hear about "Knocking" sounds. It seems to me that if you get to the point where your engine is making these noises, damage may have already occurred. I drive about 4K miles per month and would love to reduce my costs by using lower priced fuel, but is it really worth it?

rx8cited

Trust me, I don't want engine damage either ...... I've never heard any knocking or had any engine problems in my 15k miles. Also, my understanding is that the ECU compensates for lower octane fuel by adjusting the timing to prevent the knocking.

If using 87 octane is guaranteed to cause engine damage, I hope to hell that Mazda would not have said it was okay to use in the owner's manual.

If you try 87 octane and hear knocking or experience any other problems, then switch back. If you're going to try it, I'd suggest starting with Shell. Let us know what happens if you do.

steve@vivid

I'm sure somebody has said this before but I'll say it anyway. The purpose of designating different octane levels is a way of measuring HOW the fuel burns. The higher the octane the smoother and more controlled the burn. 87 tends to burn faster thus requiring more fuel and less timing. The PCM takes care of this for you learning between different fuels it can take several drive cycles for the PCM to learn though, so constantly switching is worse than sticking to one octane. For me personally running higher octane is better, there IS less risk of detonation and a performance difference. Probably not enough performance difference for the average person to notice on a close to stock car though.