I'm the proud owner of an '08 G35s 6MT (Black on Black) and am curious what kind of fuel I should be putting into it. The dealer said that they run all of their cars on 87, which I find a bit dubious, and the OM indicates premium, which I also find a bit suspect.

I also have a question about 93 Octane...I live in Maryland, which mandates a relatively high ethanol content in their fuel blends. From prior experience with a BMW that I owned, I found that I would need to use mid-grade gasoline in the winter because on cold mornings the ethanol would separate out of solution and I would get cowl shake and occasional stalling from a cold start.

So, I guess I actually have two questions:

1. Should I run this car on premium at all?
2. Anyone who is running this car on premium with high ethanol content in a cold climate notice any of the cold-start issues I experienced with the BMW?

Thanks

 

I didn't know dealers admitted using 87...

1. If I could put in 93 octane, I'd do it in a heartbeat. The best we have at most gas stations in CA is 91.

2. I don't live in a cold climate so I'm not sure, sorry.

 

Why would you think the type of gas the car's owner manual recommends you to use is suspect? Do you think they just make up stuff to recommend for no reason? You can use whatever you want, 87, 89, 91 or 93 but if the manufacturer recommends something I'd think you want to follow their guidelines.

Perhaps next you should become the proud owner of a garage to avoid those cold starts.

Haha... I'm just having fun with you. I've never had any problems starting the car but mine is garaged. And I use premium gas. Congrats on your purchase.

 

when they trying to sell you a car and if you ask that question, they will say, sure you can use 87 or 89. If you want to get the best gas mileage and don't mess your engine up, you need to use 93 Octane.

 

I wish we had 93s in California.

 

Yea, what is up with capping the octane? Thats silly

 

I can get 100 octane gas from few places here in local.... they actually have a pump for 100 octane in a station... it' in Huntington Beach BTW, they sell VP Racing 100 Octane fuel.

 

In cold climates you can get away with lower octane. For best performance use premium, but face it, Hertz has been renting G35s and the Infiniti dealers have been giving loaners out for years and they get regular **** gas and cars aren't falling apart on the road. People will talk about knock sensors and how the engine has to knock first, but I haven't seen ANY!!!!!!!!!!!!!!!! data that shows running an engine with a knock sensor recommending premium with regular causes premature failure of the engine.

I wouldn't do it on my car, but with today's ECUs and technology you could run a car on 85 octane in Denver and not have any issues short of reduced performance. Some of the cost savings will be washed up with the weaker efficiency of the engine. It's your call, but if you're trying to save a buck or two when you fill up then you bought the wrong car.

Anyone that concerned about the additional $0.20-0.30 should consider the Prius.

 

Don't you wish every gas station had 100 octane gas?

I wonder how many people would buy it.

 

1. Yes
2. No (but "cold" down here is high 20s).

 

Well the highest octane we have is 94, and that is what I pump in my car. Only one gas station sells it here in Toronto "Sunaco". Other than that my uncle works at the Airport and has access to jet fuel. He has put it in his pathfinder a couple of times and he said he noticed a huge jump in performance, but I don't know if thats true or not as I wasn't there to witness any of this. But yes generally speaking follow the manufacture guideline, from what I understand the higher the octane the more refined the gas is. Which means its more combustible and thus the computers in the car can ignite it at precisely the correct time in order to get the best performance.

 

Okay, first off, Octane is the rating given to the resistance to combustion of a given fuel mixture. You need higher octane for one reason and one reason only. To prevent, pre-detonation (aka "knocking"). Using a fuel with a higher octane rating than required is just dumb, because that leads to incomplete combustion (and you can usually smell the fuel in the exhaust).

The G35 and some other more modern cars with anti-knocking ECU technology ( by controlling ignition timing) complicate the picture. It used to be that you could start with the recommended and then slowly downgrade octane until you heard a knock then go back "up" one notch and be perfect. Now because of the advancement in motor technology, you can't really do that, so pretty much staying as close to the recommended value as possible is probably the best bet. The only thing to really do is the exhaust test. So if you can't smell the fuel at the exhaust level then, at least, you know you're not running too high of an octane.

 

Lower octake = ECU pulls timing = Less power (and less efficiency, even though you're using the same amount of fuel per stroke)

As a side effect, most customer's that I talk to report lower MPGs with lower octane, effectively negating the cost savings.

I run 91 only in my G35.

 

The best gas to use for your car is the lowest possible octane that results in 0 degrees in knock (knock being the term used to describe gasoline that ignites before its supposed to, its called knock because when it happens, it creates a distinct "knocking" or pinging sound in the engine that the driver can hear).

Of course most people don't have scanning tools to read knock nor do they have a knock gauge so they can't really measure how much knock you get, so its best to just use the recommended fuel.

Engines require different fuel because either they're turbo/supercharged or have high compression ratios (our cars falling in the latter category...306 hp out of a 3.5L V6 doesn't just come out of no where). High compression engines or engines that employ turbo/superchargers create a lot of highly compressed air...which is hot by nature. The more compressed air you have in the combustion chambers of your engine, the more violent and powerful the explosion once the gas ignites, this results in your increase in power. Since compressed air is so hot, lower octane gas may ignite before its supposed to. Higher octane gas simply burns slower hence making it less likely to prematurely ignite, its not better quality or anything. In fact, running higher octane when the car doesn't need it may actually hurt performance.

Knocking commonly occurs at wide open throttle (WOT), driving in hot conditions also increases the probability of knock occuring.

Cars these days have knock sensors which will detect engine knock and pull back the timing. The result of this is decreased fuel economy and decreased performance...and its certainly noticeable. Should your knock sensors ever fail (not likely to ever happen), then kiss the engine goodbye.

To address your second question, no I've never experienced any issues with cold starts. Our gas also has ethanol mixed in.

 

We use 95 around here as recommended by the Nissan, Infiniti Agency.