Just bought a new RX-350. Previous models said premium “recommended,” but now say “required.” Ran first tank of premium, mixed highway/city, and got just over 26 mpg. Second tank tried regular–with basically same mix of highway/city, got about 22 mpg. Doing the math, I figured regular would cost about an extra $5 for the same miles per tank of premium. Did notice a decrease in power with regular, but not significant. I do worry about your comments on high ambient temperatures (I live in Florida), and load–I’m about to do a 2,000-mile trip with four pax and seems premium would be the more prudent choice. Any thoughts?
in my 49 years of life i have heard many things about hi test and regular, here is my non scientific findings- everyone knows that the higher the octane - the harder the fuel in terms of lighting occurs- hense ping and knock eliminated by its use- low octane has lower ignition point- i have in the past found that if you mix equal parts of each, the fuel seems to act as hitest. i used to dragrace and found i could save by doing this. this is my findings and i have no evidence to verify it works- i did however not ewxperience ping or knock- this was in the 80’s too. try it and you may find it is viable way to have hitest results on a mediumtest fuel. remember how sunoco used to mix thier fuel??? hope this helps
Premium, a scam? No way! Not to us who drive turbocharged cars, or anything else with a modicum of high cylinder pressures due to high compression ratios.
I own a '93 Eclipse GSX that is my daily driver AND my weekend racer, so my boost levels see many extremes. 17-25 PSI, and sometimes 28 at the track. Puting in 87 octane piss water would be asking for detonation. On top of that, I live in California, so I have to stay smog legal & green, which I don’t mind doing (in fact, I kinda like the challenge sometimes) & I have to rely on premium gas to keep the car running in perfect tune. I often envy the 92-94 octane other states get. You can really see the difference in octane ratings at the track if you’re running a wideband O2 sensor tuning set up. We happen to be lucky to have gotten a station here in town recently that sells 100 octane pump gas for the motorcycle & off-road enthusiasts here in the desert.I often mix the 91 octane swill out here that passes for premium with the 100 octane. The difference is remarkable when the car is using its boost.
Don’t ask me to change or sell this car for a naturally aspirated car. I like the dual personality of a turbo four /all-wheel-drive car where you can get reasonable gas mileage one minute if you stay off the boost/throttle and then being able to annhilate Corvettes the next. Plus my insurance rates are for a 14 year old car… The only cars I would trade for would be OTHER turbo all wheel drive cars like the Subaru STi or the Lancer EVO, and I’ll only do so when I do my career change in to software programming when I can afford new car payments again.
I love protecting the environment, but I wish our legislators would get their heads out of their asses & give us 94 octane or more E-85 out here. (Ironically, California, the green “enviro wacko” state, only has TWO E-85 stations)The octane rating has nothing to do with pollution if your car runs like it’s supposed to. A well tuned motor IS a green motor with respect to the CO2 ouput. In fact, I would be3 willing to bet that many of my fellow import hot rodders running engine management setups like DSMLink are running far greener than most vehicles, but we’re always the first to get targeted…
I own a 2006 Cadillac STS with the 4.6L Northstar V8 with Variable Valve Timing. This engine is rated at 320 hp/315 lb-ft. The owner’s manual recommends 91-octane fuel. I started out buying premium, but switched to 87-octane regular last Summer (tentatively at first). My car now thrives on a steady diet of regular. The only circumstance where premium gives me a repeatable and measurable advantage is at the drag strip, where premium lowers my quarter-mile et by 0.2 second to 14.5 from 14.7. (Sunoco 100-octane unleaded racing fuel is even better.) I suppose that the engine computer dials ignition timing back when I really get into the throttle with regular fuel, and so increases my fuel consumption, but I have not seen a repeatable difference.
For an explanation of how a high-compression engine like the Northstar can run happily on regular, follow this link to GermanMotorCars.com and read the (lengthy) technical article on detonation and pre-ignition: http://www.germanmotorcars.com/Detonation.htm
Here on the left coast I save 20-25 cents/gallon buying regular.
You haven’t been reading the posts. The answer is, no premium will not hurt a car designed for regular. Only hurts your wallet.
Here’s some food for thought. This is what the 2007 Acura MDX manual says:
“Your vehicle is designed to operate on premium unleaded gasoline with a pump octane of 91 or higher. If this octane grade is unavailable, regular unleaded gasoline with a pump octane of 87 or higher may be used temporarily. The use of regular unleaded gasoline can cause metallic knocking noises in the engine and will result in decreased engine performance. The long-term use of regular-grade gasoline can lead to engine damage.”
When one of the top engine-builders on the planet uses the words “engine damage”, it certainly gets my attention.
Very good info. You have just proven what others are saying here. If you use a lower octane than recommended and you don’t like the result, (in either general performance or pinging), move up. Otherwise stay put.
Others want to move into in-depth analyses on mpg or drag-strip elapsed times. Fine. It is up to you. Point is, you are in charge given the pertinent facts.
Good point. How do I check the octane of my gasoline?
If the RPM goes up with a constant speed, then you have a problem with a slipping clutch!
I agree with this metric. I have a 2003 Acura TL-S. I tried running with regular for several months and compared the gas mileage (MPG) vs. using premium. I saw over 10% reduction in MPG. Now when gas was around $2/gallon the 0.30/gallon difference made sense to try regular. Now with gas over $3 for regular and $3.30 for premium it makes economic sense to stay with premium since I get more than 10% better MPG with premium for only a 10% price difference.
2005 + Mustang GT’s call for 87 octane. However, using higher octane gas has shown marginal inprovments on the dyno, roughly five RWHP or so. Is is worth the extra cash per year? Dunno, but it does show that higher octane gas can occasionally be better for your car.
The Neon’s engine control computer is very good at ‘taking advantage’ of higher octane fuel (or, to put it the other way, it retards the heck out of the timing when it’s fed regular). For what it’s worth, I think the octane makes a bigger difference in the DOHC-engined Neons rather than the SOHC ones.
…Or, if it’s an automatic transmission, it could be that the engine is delivering more power, thereby allowing it to maintain a given speed in a higher gear (or even just the unlocked/locked state of the lockup torque converter).
In the first scenario, the engine is developing less power, so the driver is standing on the throttle to make it go, and the transmission is accommodating with a less-than-top gear choice. In the second, the throttle doesn’t have to be worked as hard because the better-running engine can develop enough power to maintain highway speed without as much pressure on the gas pedal, so the transmission can shift and maintain a higher gear.
My 2003 Mercedes C230 Kompressor’s manual bears a similar warning, though the only language on the filler door is PREMIUM FUEL REQUIRED.
Given that the car gets 30+ mpg on the highway, the incremental cost of premium fuel is a small price to pay to help avoid engine damage. Compare with my wife’s car which gets about 27 mpg, but takes regular gas, and I think it’s about even.
I used premium in my BMW for a few months then I tried a tank of 87 and well it wasn’t quite the ultimate driving machine after that. I use mine for racing, I didn’t buy a monster to putz around and never floor it, I drive the living sh1t out of that car and believe me there is a big difference between 87 and 91 octane.
It’s the government’s fault.
In the old days more power could be obtained by simply making bigger and bigger engines. With the CAFE and Clean Air Act statutes to comply with and the power contained in the gasoline already being used as effectively as possible (as evidenced by the low unburned HC and low CO outputs, the only ways to get more power out of the engine are increased compression and a technical trick here and there (like variable valve timing). And increased compression requires better octane.
So I blame the government.
- mountainbike
I have a 2005 RX-8 and tried running 87 octane in it. Hard to tell if a rotary is knocking, but my mileage went into the toilet. 30% less with 87 vs. 91 octane. I only use “premium” anymore. For my car’s engine, it’s cheaper.
dave
All gas has mandated(US) levels of detergents. Very few if any cars are going to need more.
Remember you could be loosing performance and mileage
It’s a case by case basis. If someone has a car that pings on 87 does this mean the gasoline is at fault?
Not necessarily. Carboned up engine, clogged EGR passages, faulty knock sensor, improperly set timing on distributor equipped models, etc can all contribute to that problem.
Premium is recommended for my Lincoln Mark.
It’s been living on 87, and less, for 120k miles now and has never suffered a hiccup, loss of power, mileage, or anything else due to 87.
Numerous trips through the Colorado Rockies running 85 octane, pulling 6-7% grades in summer with a load, and not a peep out of it,while still maintaining 27 MPG.