I think it’ll depend on the vehicle but I wouldn’t use higher octane than needed.
However for “downgrading”, I’d consider testing one grade down for 3-4 tankfuls of typical driving - once in summer, again in winter. I did this with my 1995 Toyota Avalon and found that it made a 2.5 MPG difference (I have a light foot on acceleration and braking and time lights and traffic).
My typical driving pattern mileage is 27.5 with 89 octane and 25.0 with 87, so I am better off as long as the price differential between 87 and 89 is 10% or less which is always at today’s pricing.
The Avalon has 245,000 miles on it, with its first belt/hose/spark plug replacement at 215000. The plugs were still nice and nut-brown with the electrodes still in good visual shape.
I think that in addition to good fresh fuel, scheduled filters and fluid changes are important to maintain engine health. A couple of extra pounds in the tires also help, and don’t result in any abnormal wear on my vehicles.
I do have a question, though - can oxygen sensors affect engine tuning and not trigger the engine light? My “all freeway” mileage went from 31+ MPG to 29+ MPG, and I’m wondering if any sensors might be deteriorating and causing some mistuning by the computer system.
I noticed the drop shortly after the replacement of the timing belt, idler, water pump and plugs so could it also be something related to that work?
Let me preface my remarks by stating that the sum of my research into this topic consisted of reading the first couple of dozen responses. However, much like Tom and Ray, I do my best theorizing when completely unimcumbered by any actual data.
I think that there is a consensus that any modern car is capable of retarding its timing such that 87 octane will do no significant damage. However, it seems likely that a car running with retarded timing will get poorer gas mileage.
No one seems to have actually done the only test that matters, which is a carefully controlled and documented mileage test.
The BTU per gallon argument looses some of its luster when you consider the reasons why a gasoline engine is only about 25% efficient. Fuel that burns slowly and evenly is likely to transfer more of its energy to the piston. When you are throwing away 75% of your energy, increasing that waste by even a few percent has a dramatic effect on economy. If your car is turbocharged and recovers more energy from hotter exhaust, this discussion gets more complex.
In conclusion, I have no idea what the answer is, but I know that today at Costco, the difference between 87 and 91 octane was $4.20 vs $4.45, or about 5 1/2%. I know that when I burn 87 octane in my wife’s 330 BMW, the difference in performance is noticeable. With a 5 1/2% price difference, if her mileage drops from 26 mpg to 24.5 mpg, then I have lost the money I saved buying regular, AND the car runs poorly.
This is what keeps me away from those good german cars & other performance fun cars Premium is 40 cents/gal more than $4.00 regular. A question I always wanted to know was what if you downgrade to 89? Will there be long term effects/damage. At Toyota & Subaru the mechanics seem to prefer 89 implying less carbon build up & wear to engines. I use toptiergas.com as my guide and use Shell gas as we don’t have any other top tier gasoline co’s in Northeast PA. We have Valero, Lukoil, Sheetz, Sunoco all of which suck and give poor performance/20% less mileage. Took techron and 1-2 tankfulls of Shell to restore power and mileage. 89 doesn’t seem to boost performance or mileage noticeably. Someone who knows please help put me straight
The Regular vs. Premium debate is now just fodder for automotive columnist to fill up space. Too lazy to write a fresh column. Stick in the Premium vs. Regular debate. Just be sure to use the weasel words. “Probably” won’t void your warranty. “We don’t believe” it will hurt your motor. But hey, it’s not our car and we got another free column.
Truth is, if you wanted a car that runs on regular, why didn’t you buy one?
I have been driving a 96 Saturn SL2 for a number of years. I used to always put mid grade in and started checking my fuel economy. I checked every tank and got it down to a science. Then I switched to premium gas and my fuel mileage jumped by 1.5 miles per gallon. With the fuel prices the way it is I was saving 80 cents per tank using premium and I have never had a issue with anything. I now have a 2008 Nissan Sentra and am going to try it on this one. I think this using regular gas is a joke. I’ve had better fuel economy and better running car with now harm to the emission system or anything else on the car.
it makes me laugh when people spend many thousands on a new car then put the cheapest crappy petrol in their cars!!!here in england descent petrol is ?5.00 a gallon,thats almost $10.00!!!but rather than save 1 pound per tankfull by putting cheap supermarket fuel in,i always use high octane from b.p or shell.come on guys dont your cars deserve the best?especially when your gasoline is so cheap!!!
in england a bmw 330i outputs 221bhp on 95 octane petrol,and 231bhp on 97 octane,so that proves it makes a diffrence by using a higher octane.and ive been told that our ratings are higher than in the usa,so i guess 97 is like your 91 over here?
If your government wouldn’t tax your petrol so much, you’d be paying roughly the same prices we’re paying in America. We dumped our tea into the ocean and called it a revolution, we dump our oil into the ocean and they call it the Valdez.
I was going to call in. I have a 2001 VW Passat with a 1.8L 4 cylinder turbo. I love this car. It’s drives great and has wonderful pickup despite its rather small engine. And although it is a thrill to drive, I can get about 32mpg on the highway if I drive carefully. If I drive like the rest of the people in New Jersey, I get about 29-30 mpg.
I’ve always used premium fuel since the owner’s manual recommends at least 91 octane. Premium is around 93 octane, but mid-grade is only 89 octane.
My son started driving, and told me that the car doesn’t need premium fuel since the owners manual only “recommends” 91 octane. And, the owner’s manual even goes on to say “never put in fuel under 87 octane”. Therefore, he claims, it is okay to put in regular gas which is 87 octane. Yes, my son is planning to be a lawyer when he grows up.
I remember a call to cartalk about 5 years ago where someone asked if it was okay to use regular when the owner’s manual said to use Premium, and you two said that if the owner’s manual said premium, you should stick to premium.
We decided to experiment, and my son put in regular. There was no knocking, but the car was sluggish, and the gas mileage went down. We’ve switched to mid-grade, and the car seems fine. It has pretty good pick up again, and the mileage went back up, but I’ve been a bit leery ever since, and was thinking of calling in.
Thanks to this thread, I now feel better about putting mid-grade into this car. The car’s performance and gas mileage is fine. It might be a bit better with premium, but I’m not so sure it’s worth the 30 extra cents per gallon.
Mileage tests on my 1994 Ranger show about 22 mpg on Premium and 20 on Regular. If the price delta is less than 10%, it is not only more economical to use Premium, but there’s no knocking!
I’m sure that the oil company marketing gurus have designed premium as some s0rt of ploy, but the fact is I get 13% better mileage with 89 octane than 87 (2006 Nissan Maxima). So when the price difference is 13% or less,… (To be honest, I haven’t checked the mileaage with 91 octane.)
Premium is a relative bargain today! The price spread between grades is the same as it was two years ago, but gas has doubled. The additional cost as a percentage over the price of Regular is half of what it was.
My cars and pickup all do fine on regular but my Harley (2007 fuel injected) really likes premium better. So run the good stuff in it. It’s gets about 50mpg so it’s no biggie.
But I wonder…do most people shop for gas by price? by brand? or what?
If you shop by price do you also run the cheapest oil in your engine with no regard to it’s quality?
If you don’t know what oil is in your engine right you may be asking for trouble.
I might run cheap gas…but always the best oil…and filters.
I’ve read that for later cars it doesn’t matter what fuel octane you use they adjust for that. Maybe premium is a ploy. I don’t think so. I use premium, both high mileage, in a ‘92’ Ford truck and a ‘2000’ GM passenger car. I have never had any fuel or engine problems associated with either vehicle. Maybe it’s good luck. But, I also own(ed) a ‘92’ and ‘96’ GM passenger cars and used regular fuel in both. I’ve encountered numerous check engine problems with both. It could be bad cars, but the fuel has had something to do with it.
Compression will be higher at LOW altitudes thus requiring higher octane rating. Compression (or more properly combustion chamber pressure) will degrade at higher altitudes due to the thin air. (not as much stuff to compress) and thus allow lower octane fuel to run without spark retard or spark knock. In this case, you had it exactly backwards. This is why mountain states will have lower octane rated fuels.
But I do agree that in the old days, muscle cars ran on the high test (premium) because of the high compression engines with which they were supplied. Higher octane fuels resist preignition. In the good/bad old days, high compression was really high (as you stated, 12/1 not uncommon) but high test fuels were capable of dealing with this compression ratio due to the addition of (more)tetraethyl lead to increase the octane rating. Octane ratings of 100 or so were not uncommon. Nowadays, there aren’t any engines with 12/1 because tetraethyl lead had been eliminated as an octane enhancer. Now, octane ratings of 93 are pretty much the high end. Compression ratios even in performance cars are lower. (Lower compression ratios also help to lower NOx production which contriubute to smog.) Thus, spark retarding enables a modern performance engine to run on lower octane rated fuel, but with less power.
Bottom line: if your engine/owner’s manual/gas door calls for high octane fuel, there is a reason for that. Use premium fuel for best performance and fuel economy,. If your engine/owner’s manual/gas door does not specify premium fuel, there is no reason to use it. You will not “gunk up” the engine, and you will not gain any performance by using premium.
And up to a point, it is true that carbon deposites will cause an increase in combustion chamber pressure (by lowering the volume of the chamber) but this will happen on low or high octane fuels. It just happens. (Yes, some fuel additives are said to decrease carbon deposites). But carbon will build and increase pressures until the valves and piston rings wear at which point combustion chamber pressures will begin to decrease.
Premuim fuels is only called premium because of its ability to resist preignition. It has no more heat (btu’s) per gallon than regular.
Turbochargers don’t care about exhuast heat, but exhaust speed (volume). Actually, the cooler the exhaust the better. The gas is more dense and spins the impeller better, plus it imparts less heat to the compressed air.
i have a 2001 mitsu montero ltd. it says premium fuel only. i started using 87 octaine after the firs 2 tanks. i weined it off of premium by adding more and more 87 to the mix untill it was completly converted. its been 129,000 miles and the ONLY thing ive had to replace was the rear heater pipes. i get 16.5 average mpg and mine does zero to sixty in about 8 sec. iv had no loss of power whatsoever neither has my mother who drives a vehicle rated for premium only aswell.
