Ok, In my '91 Toyota V6 truck I used to always run what is called "marked gas" - - it's just 89 octane fuel with purple dye in it. It's sometimes called "marine gas" and isn't supposed to be used on the roads because there's no road tax built in to it. It's cheraper than regular 87 octane. Maximas call for 91 octane fuel, but the owner's manual says that they will run, but not recommended, on lower octane fuel. My local dealer says there are lots of Max's running around on midrade ('89). I've run about 4 tanks of 89 octane marked gas in my Max with no problems as it's about 15% cheaper than 91. I've never had any knocking. If I were to run high RPMS a lot, I'd run 91, but I rarely exceed 3000 rpm. Anyone else ever run marked gas? Any comments on marked gas being ok or not?

 

I believe that if you listen closely you will hear knocking when starting up from a standstill. My 98 does. The only cure is 93 octane. what are we talking about, maybe $1100/yr in fuel, 15000 milea @ 1.489/gal. So 15% of that is a savings of $165, which would be $13.75/month. Not even enough to take a date to a movie for an evening, let alone for a month.

I don't think it's harmful, as Nissan does not state that premium is required. It is "recommended." BMW says premium is REQUIRED. I read in my grandma's chevy caprice's owners manual that knocking is normal and NOT harmful to the motor. At least that's Chevy. It's really a personal preference though. People on this forum waste $165 in a single traffic ticket, so I wouldn't go out of my way to save the 15% you mention. my 02

 

Agree with frank, if you wanted to save a few bux, trade for an altima. Seriously, if your not a real performance person, lower octane will be ok.

For a few dollars I would not do it, especially if I noticed any knocking.

 

My car got worse milage (3-4 mpg) with lower octane fuel. I've got about 25 fill-ups in a spreadsheet that show this.

 

how does the dealer know who puts what in their tank?

 

The local dealer has you fill out a form that asks what grade fuel is used on a regular basis.

 

Wait a second.
We won't hear knocking because we have knock sensors that retard our timeing. When a low octane fuel is used we just loose a substantial amount of performace because the timming has to be retarded so we don't ping. I believe we have a 10:1 compression ratio which is rather high which needs higher octane fuel.
there are dynos or track times to prove the effectiveness of higher octane fuel. Always use 91+ octane.
If this is not right educated me.

 

You will hear knocking when you start up from a light with the max when running 87, and also when you go uphill even at 3500 rmp etc. I have heard it. And it's also true, for the early 90's Chevy Caprice the owner's manual states that knocking is normal and not to be concerned, and above 87 octane is not necessary for that car.

Any dealer that wants me to sign a form stating what grade of petrol I used can go **** themselves. Who in their right mind is gonna sign something like that? They ought to sign a form stating how many people they ripped off in a lifetime of shady sales.

 

The dealer uses this when trying to diagnose problems with noises - it's a checklist to help them diagnose. I agree with you though!

 

You're right. But, in order for ur knock sensors to work, there must be an initial "knock" before timing is retarded, and this initial one can cause damage. 87 octane, I agree, is too low for the Max unless it's occasional and you baby it. But this 89 midgrade marked gas? I've yet to hear a knock, even at start up. I'll run some premium again and compare...

 

Marked gas may or may not have the detergents/injector cleaners that road cars want. Adding it yourself works but now you gave back some of the 15%.
Knock is not a function of RPM, but load. It is possible to drive gently enough to avoid knock or resultant spark retard with lower octane gas but that's pretty gentle. You will suffer some MPG loss compared to 91 because of the retard, giving back more of the 15% savings. Light knock is not good for the engine, but it's not disastrously damaging either, it just doesn't seem that the marginal savings are worth the risk.

Or, as I always say, "If you want to drive retarded, use lower octane."