Grumpa72

I agree. Almost all cars today that require premium will run perfectly well on mid or regular low. The engine has a knock sensor and lowers timing and other engine parameters to allow you to SAFELY use a lower octane level. The need for premium is merely to get maximum horsepower. This is driven by marketing, imho. Lower the octane rating and you lower the horsepower but not necessarily the mpg's. I doubt that most of us drive our cars to the edge and really need all the horses.

Gary

32kcolors

Given that, are any of you RX350 owners brave enough to drive your car on regular?

IS350_PHIL

iTrader: (2)

My wife's had regular for the first 3 tanks and did not suffer any ill effects that I can tell. Now that she saw the little sticker on the fuel door, she is only putting super in the tank. I wonder if you used regular unleaded long term if there would be any problems...

neverest

There shouldn't be. It's not like regular fuel is any worse than super in quality - it's just different octanes. If the ECU compensates for it, over time it will most likely adapt into that setting, robbing your car of horses, but it shouldn't do damage. Nevertheless, if the engine is designed to put out a set number of horses, why should a self-respecting Lexus owner deprive the engine of its horses by putting in regular?

I mean, this IS a Lexus forum. All of us paid good amounts of money for our beloved cars. Is ~20c/gal cost different really that prohibitive for most of us, at the expense of power that the car was designed for? I'll just eat the price difference.

USLEX

I have run my LS430 on regular from day 1. Not a problem at all and it accellerates better than I want.

lexusman1

I run my 2003 GS300 using only BP or other higher brand gases with high octane BP has an impressive 93 octane. compared with other gas stations selling premium with lower octanes like 91 I kinda afraid to use anything but premium in my lexus after all i payed premium dollar for the car the least I could do is reward it with what it wants which is premium. I believe in If you treat a car with respect you get good results and if you neglect than if somethings acts up mechanically dont whine or cry u only can expect the worse. I've heard some rumors and myths from people who own other brands of cars from germany(m-benz,audi,porche,bmw)who say they've tried using regular grade gas (87-89) octane and got bad results mechanically with the engine parts. I dont know if the same applies to us after all we own vehicles engineered by the japanese they're built totally different. But I rather not take that chance and find out the hard way I payed to much in to this car for it to act up.

TunedRX300

Can someone please explain why 2006 Toyota Avalon, which has the same 2gr-fe engine as RX350, requires octane rating 87?
http://www.automotive.com/2006/12/to...ons/index.html
Don't tell me Lexus put a premium requirement so RX350 owners feel they have a better engine...

USLEX

Any automotive engineer will tell you that it doesn't matter besides a slight loss in horsepower. Pay for Premium and drag race, I'll stick to regular and a secoond behind you

TunedRX300

No, Toyota put the same engine in Avalon and RX350. If regular (gosh, that sound so cheap) is required for Avalon, premium (man, that sound so much better) is not needed for RX350. Unless it can sell cars...hmm...to those who are willing to "pay good amounts of money"?

neverest

Comparing the Avalon's 2GR-FE and RX350's:

Avalon:
268 hp @ 6200 rpm
248 lb.-ft. @ 4700 rpm
Compression Ratio: 10.8:1
Recommended fuel: 87 octane

RX350:
270 hp @ 6200 rpm
251 lb.-ft @ 4700 rpm
Compression Ratio: 10.8:1
Recommended fuel: 91 octane

So, in short, it seems to me that the reason why premium fuel is recommended for the Lexus's engine, which has the same compression ratio (which usually dictates what kind of fuel needs to be used) as the Avalon's, is that with a higher grade octane, the engine is able to squeeze out 2 more hp and 3 more lb.-ft of engine power. It goes on without saying that without the premium fuel, you will lose that engine performance, but it should hold up fine, with no repercussions, as I previously said with regular fuel.

Interesting footnote found on Lexus's RX350 site:
"Ratings achieved using the required premium unleaded gasoline with an octane rating of 91 or higher. If premium fuel is not used, performance will decrease."

Implies no warning regarding engine malfunction.

TunedRX300

Actually the HP and Torque difference can also be caused by difference in intake and exhaust design.
Official dyno from www.lexus.jp you will see IS350's hp/tc differ slightly than those of GS350, they both have 2gr-fse motor and using same fuel.

neverest

You're right, I stand corrected. However, intake and exhaust design won't necessarily dictate the type of fuel that must be used - although I suppose if the fuel-air mix is different, that may be why premium is required.

At any rate, I'll be putting 91-93 octane on mine. No reason not to - just put in what it was designed for.

CK6Speed

iTrader: (1)

While others may not agree, I do get better fuel economy using premium with our RX330. They way I figure my MPG is to zero my trip meter at every fill up. I then fill the tank and divide the gallons going into the tank by the miles traveled. Since I do this at every single fill up, it gives me a very accurate average MPG. With premium I get XX, and the last time I tried 89 for a couple of weeks I got XX-2. In other words. I got about 2 MPG less than with premium gas. The very next tank that was filled with premium again yielded my usual average. Thus, I conclude that I get better fuel economy with premium. I know we all don't drive our cars to the edge, but you don't have to drive it 100% to utilize what performance the engine can provide. Often you will notice the difference when going up hills or passing. For those that have tried types of gas themselves and documented no change I envy you. I wish my RX330 behved the same.

Just to add, E10 gas has dropped my fuel economy again as well. I no longer can get the mileage I used to. This happened within a matter of weeks when our state required all gas to have E10.

TunedRX300

Yes, intake and exhaust do not change fuel requirement, just allow the motor to breath better.
I suggest those who are interested in this topic to search on the maintenace forum. You will find some gets worse mpg, some better mpg but not to the same % difference in $ . The most interesting post to me is one year Lexus changed fuel requirement on the ES to premium, whereas all previous years requires regular and above, with no change in design (same generation).
At the end of the day, what one puts into his car is his personal choice. Do whatever makes you happy

Grumpa72

I drive my Acura, which requires premium, on regular. Have been doing it for years and it continues to run fine.

Gary
05 330 (running on regular)