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Here is a weird situation I have an 06 automatic G35. If I used 87 Octane and put in about 16 gallons I can get 300-350 miles from it. If I put in the same 16 gallons using 91/93 Octane my gas mileage is terrible; I’m talking like 200 miles if I’m lucky. I have done this three or four times from different gas stations with the same results. I changed the spark plugs recently and the engine doesn’t knock or ping everything seems fine. I’m just curious if this a problem since my car was designed for premium fuel only.
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I’m not an expert, but I don’t think it’s a problem. Your engine just happens to like that fuel better. My understanding of octane was that the higher the octane the more resistant to burning it is. Meaning that the compression of the engine is less likely to cause it to burn at the wrong time. Maybe after wearing some your engine compression and spark timing is more compatible with the lower octane. Personally I wouldn’t worry about it, but there’s a lot more knowledgeable people on this forum.
Thanks for the response. That’s what I’m hoping, I was just curious if could possibly be a sign of my engine not combusting the premium fuel properly or something. I can literally watch the needle drop as I drive after putting premium in.
I understand the point of octane, but I’m mostly concerned about the drastic difference in MPG. I don’t experience any misfires, knocks, pings, or too lean/rich codes. The only difference I see is in my wallet and MPG, lol. I’m mostly concerned with since it burns through the high octane so fast (I can literally watch it go from full to half) how can I know it’s all being used properly (if that makes sense)? Would I need to have my air-to-fuel ratio measured or something? But, since the engine seems to be perfectly fine with each and doesn’t act up can I just assume everything is okay?
This is a stretch but if you’re getting your fuel from the same place when you fill up that could be the issue. Perhaps there’s more sediment or moisture in the Premium fuel tank in the ground than in the 87 tank. This might be the cause. You might try filling up somewhere else just to see if you have the same issue. Keep us posted.
Ahh the man himself responds, lol. Just wanted to say thanks for your videos they are awesome and I have learned a lot and especially the little tricks when something doesn’t go right. Unfortunately, I have tried that and have used several different gas stations in two different states.
I did fix the following today that I noticed wrong with my car, but not sure if it would have affected the difference in octane. Replaced both front calipers one was sticking and the other looked like it was slightly shaving the top of my new rotor at an angle. Installed two new struts and replaced two failing lower ball joints.
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