View Full Version : More on gas...
08-16-2000, 08:19 AM
I was reminded of this by reading another thread. On the inside of my gas tank cover thingy it says "Premium recommended for best performance." I've been making a 50+ mile commute for the past few years, and I couldn't justify the extra cost. Now that I live about 10 miles from work, I don't see that being a problem, which leads to 2 questions.
1) Since it seems to recommend premium gas, will I really get better performance?
2) Are there problems with just switching gas like that? Should I get my current tank as low as possible? With the extreme difference in octane, will it not burn as well mixed?
OK. That's like 4 questions. So, who's done this?
08-16-2000, 08:28 AM
With my previous car, switching from regular to mid-grade had no noticeable difference (I had hopes that things were running cleaner/better). The manual for my current car recommends AGAINST using premium grade gasoline.
08-16-2000, 08:58 AM
As is mentioned in the other gas thread, if your car is not designed to run on high octane (and is in good running order) then using premium gas will get you no better milage, will cost more, and could do your engine harm.
Several gas chains have been sued for misleading advertising for making "performance" claims for premium gas. On most cars, it's simply not true.
08-16-2000, 09:07 AM
On the other hand, some cars _are_ designed for it. I believe the Corvette's are still requiring 92 octaine.
I love watching Adam-12. Stop a robbery at a gas station, get a look at those lovely old pumps, putting out 102 octaine Leaded for a mere 25cents. Droool.
08-16-2000, 09:12 AM
One of the dealership (a Chevy-Pontiac-Oldsmobile dealer) mechanics to whome I have spoken before warned me about using anything other than the lowest, 87 or so octane gasoline (that means no mid-grade, no premium) in my small-engine car (4-cylinder Pont. Sunfire). They weren't designed for those octane levels, and the gas will burn too hot, causing whatever damage will occur from the cylinders exploding at too high a temperature. I assume this could include warping, cracking, etc. My father, however, has a big ol' honkin' SUV that, as if it doesn't burn enough gasoline in the first place, recommends that it be filled with higher octane gas. When I take it to the gas station for him though, seeing as how gas here in Illinois was almost $2.00 a gallon for even the cheapest stuff, I cheated him (maybe) and filled it up with the lower-octane gas so he could get a full tank for under $40. I figured he didn't pull a trailer or use it for anything else halfway strenuous, and he really never even could tell the difference.
08-16-2000, 09:18 AM
Thanks for the advice, but that's just the thing. I think my car is designed to run on high octane. For reference, it's a 1997 Nissan Maxima. With this particular car in mind, will it hurt?
08-16-2000, 09:42 AM
I feel your pain. I have made modifications to my truck that require me to run premium fuel
Here's the scoop as I understand it. If your car is designed or tuned to run the higher octane, you may actually cause damage to your car by running the lower octane gasoline. This is unlikely unless you drive your car hard, though.
The problem with the lower octane fuel is that it burns faster and more violently (Yes, that is right), which in some instances can cause detonation and nasty knocking in the cylinders, eventually leading to big problems if you let it continue.
The higher octane stuff burns more slowly and more controlled, which often results in more even power. Switching back to the higher octane will not hurt it in the least. It MAY perform a little differently as the computer adjusts, but after driving for a little while, all will be normal again.
08-16-2000, 10:18 AM
If your car is designed to burn premium gas, you should use that. Lower octane gas can ignite before the spark plug fires in a high compression engine, causing knocking. This can damage an engine, costing far more money than you save in lower gas prices.
Some engines have "knock sensors" that can detect when this is occuring and changes the timing in some way, preventing any damage. But you lose power and it may not be good for the engine in the long run.
For your 97 Maxima, does the owners manual say anything about damage or just about performance? If all it talks about is better performance, and you don't hear or feel and knocking, than you probably are OK with lower octane than recommended. But you can't always hear knock, so I'd check with the dealer or a good mechanic that knows your car.
08-16-2000, 11:42 AM
Regarding gas for your car:
1. Use the octane recommended by the manufacturer, and stick with it. If it says to use premium, then I would use it. But there is absolutely no advantage using 93 octane if your engine is designed to run on 87 octane.
2. Try to make it a habit to fill-up at the busiest gas station you can find. Busy gas stations refill their tanks more often, and thus there is less likelihood of water getting into the gas (via leaks or condensation on the sides of the tanks' walls).
08-16-2000, 01:23 PM
Cool. I think I'm just going to do it. The manual does say recommended, though not required. But, since I've put 113,000 miles on it in less than 4 years I'm going to just do everything I can to keep it running smoothly. I've never had to do a repair on it before, and I intend to keep it that way. Thanks for the advice.
Here try this link from the Federal Trade Commission (http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm).
08-16-2000, 05:30 PM
Find out for yourself. Fill up with regular unleaded and drive your regular commute for a week. Record your mileage for that tank. Next time, fill up with high octane and run your regular commute.
08-16-2000, 07:10 PM
I drive a 1996 Chevy Impala SS which has the same LT-1 engine (and bad gas mileage...a whopping 15mpg) as the Corvette. Yet, as has been suggested earlier, the Corvette manual specificly tells you to ONLY run the premium stuff while my manual is a little less specific and says only to use a gas of octane 87 or more.
So, if it truly is the same engine (and I can't totally vouch for that) then it sounds like Corvette owners are being fed a line of crap because I use the cheap stuff and my car runs great (less the wierd cooling problems I wrote about in a thread about two weeks ago that many Chevys seem to have)
08-16-2000, 07:56 PM
More information on octane (http://www.howstuffworks.com/question90.htm)
08-16-2000, 08:00 PM
Another issue that can come into play is altitude. At high altitude, you should use a lower octane. (Less oxygen in the air makes fuel ignite less easily, lower numbers ignite more easily to compensate for this.) This is reflected in what stations offer. The low grade at a typical sea level pump is 87; driving across the Rockies at about a mile up most stations were selling 85.5 as the low grade. The other grades were scaled down too, I think. My car ran well on 85.5 at high altitude.
My understanding is that it's worst for the engine to run with fuel with an octane rating that's too low (which causes premature combustion, causing pinging and poor milage.) Running a car with higher-than-necessary octane fuel is bad for milage as well but less harmful to the engine, or so I'm told.
For the OP: IMO it seems likely that the gas you were using, that got you 113,000 miles without repairing your car, is not too low in octane. I wouldn't change what you were doing. (IANA mechanic)
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