Da Hapa

I know the owners manual states that 87 is fine but you can get better performance with higher octane rated gas.

Sadly, here in CA, we're limited to 91 octane but what do you guys/gals use and why?

Is anyone actually noticing better mileage and/or performance with higher octane gas?

Thanks for your input in advance.

Christian

LexRX

This topic has been covered so many times it makes my head spin. The general consensus is that there isn't one. Use whatever gas you want. Like you said, the manual states 87 octane can be used, but 91 is recommended for improved performance. Some cars are designed to run only regular gas and premium is a waste - I don't think this is the case with the RX (as you can see in the manual).

Everyone will have an opinion on the subject, some reasoned, some not. All I'll give you is my choice and that is to run 92 or 93 octane (i.e. premium grade). That is based on the recommendation in the owner's manual. I have a FWD, drive fairly conservatively on the highway and realize an average of over 26 and sometimes over 27 mpg on the highway at speeds between 65 and 75 mph.

The only difference from stock is a Rod Millen Stainless Exhaust and I use Mobile 1 5w-30 synthetic oil. I must be doing something right.

JRB

Or another alternative is to buy mid-grade, which in this area is 89 or 90. This is what our dealer recommended, and the car seems to perform real well with it.

ederny

Da, Just remember

Premium is for Peformance.

When is performance used? At wide open throttle (WOT) - like in passing vehicles on narrow roads. There is a measurable difference in these cases, you may not notice it yourself. Bottom line, for normal driving there is no need to spend the money.

If you are interested in more on this, just do a search on gas milage on this forum or read the articles at Item A 4

Da Hapa

Hi guys -

Thanks for the feedback so far.

To clarrify, and in hopes of gettting your continued input and discussion let me state a couple of things that contributed to me posting this thread.

1) Unlike our IS300, LS400 and S2000 (which all specify the use of 91 octane or higher gasoline), the RX's owners manual only says 87 but better performance can be attained with premium fuel.

2) My experience with a now gone but much loved 1990 Miata taught me that putting a higher octane fuel in a car that didn't need it was akin to burning money. Granted a miata isn't the same thing as an RX but I guarantee you that I drove the snot out of that Miata and it didn't perform any better or get any better gas mileage on 91 than it did on 87. The Miata Club did a scientific study on this topic and came back with the same conclusions.

In fact, the article that ederny pointed me to substantiates that by saying "Once you have identified the fuel that keeps the engine at optimum settings, there is no advantage in moving to an even higher octane fuel. The manufacturer's recommendation is conservative, so you may be able to carefully reduce the fuel octane". Thanks for the article, btw, Ed.

3) In CA, we're limited to 91 octane as premium anyway.

So... I asked the question because I'm hoping that some of you might have emprical or personal experience telling me whether you get better mileage with premium, increased performance, etc. I'm not so cheap that the extra 15 cents per gallon will kill me but at the same time, I'm also not a big fan of just throwing money down the drain.

(Side note - the dealership told me two separate things. The service advisor told me 91 octane or higher. The master service tech told me that unless its really hot outside, 87 octane is more than fine.)

Your thoughts???

jcg

Had a 2000 rx untill last week when I picked a 2004. on the 2000 I was inroute from NY to FL one time when I was filling up and realized that I was pumping hi-test instead of my normal 87 octain. This was after I had filled the tank which had been almost empty.

From that tank I got no better milage and could not differentiate any difference in power. So, I use nothing but 87. I have never heard a ping from the engine.

mikey00

I tried 87 octane and premium in both my 2000 and 2001 RX. I found no difference in gas mileage or performance. If you feel a difference with premium it is just because your wallet is lighter.

SteveH

I have a 99 with 48K miles and have tried all three gas octanes and have not seen
any difference in gas mileage or "performance". I just came back from a long trip down south
and used prem all the way and the mileage 16 to 23 and speed was from 55 to 75 with
mostly flat terrain. Here in the city I have been using 87 and average 16 to 17 with a combination
of city and highway but mostly city and 92 was any better.

I would really like to know how everyone else is getting 20+mpg?

Mine is pure stock and has regular oil changes and Lexus maintenance, so if there
is some thing I can do to get better average gas mileage I would really like to know.

mikey00

There are so many variables affecting mileage it is difficult to do a comparison here. The people reporting the better mileage often are one or more of the following: very light on the gas pedal, drive more country or highway than city, don't live in high altitude, have FWD (which they neglect to tell you when they post their mileage). I average 19.7 (AWD) and drive about 80% country roads, 19% city and 1% or less highway. The best mileage seems to come at around 55-60 on the highway. The RX is geared lower than most cars I have driven and the RPM's really start to go up at higher speeds and the mileage goes down.

LexRX

Mikey, I hope you are not referring to me here. I always cringe when people ask for and post gas mileage statistics - there are many variables that are often left out.

At any rate, concerning octane ratings for the RX, it is really up to you whether you want to use regular, mid-grade, or premium. The RX engine is a high(er) compression engine. High compression engines are designed to use a high octane fuel. Using regular, however, will not be detrimental as the computer controls on the engine will change (or retard) the engine timing so that there is no pinging. High octane gases are more difficult to ignite (require higher pressure than, say, 87 octane - therefore a high compression engine is necessary to take advantage of 91+ octane). High octane gas also burns longer, hotter - creates more pressure.

Here is an exerpt fromt the Star Tribune that explains it well. The full article has some great information:
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http://www.startribune.com/stories/435/1622112.html
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"Now, here's the catch. Higher-octane gasoline requires more heat and pressure to ignite, meaning it's actually harder to ignite. That's why higher-octane fuel is less prone to pinging. This also is why high-performance engines with rlatively high compression ratios require higher-octane fuel. These engines develop higher combustion pressures and temperatures, which would cause lower-octane fuels to "pre-ignite."

The primary characteristic of higher-octane fuels is longer hydrocarbon molecules. These are stabler and more difficult to ignite, but when they do ignite they burn slower, producing higher cylinder pressures. To capitalize on higher-octane fuel, the engine must be set up with more compression and in many cases, more ignition timing."
-----------------------------------------------------

EDIT: Okay, so you have to register to view the page - somehow I was able to pull it up before without registering. If you have the time, still a good article.

You may also want to check out this article about compression ratios and the proper octane. It may be something you want to try:
http://www.leeric.lsu.edu/bgbb/7/ecep/trans/b/b.htm

FWI, the compression ratio for the RX300's engine is 10.5:1. The RX330's is up to 10.8:1 - those are relatively high numbers and usually seen in natually aspirated high performance engines (Honda S2000: 11.7:1; Murcielago: 10.7:1) This is part of what allows the RX to get a decent amount of power out of a 3.0 liter engine.

mikey00

Sorry if it appeared I was referring to any individual. I was making a general statement. All too often I see a AWD RX unknowingly comparing mileage with a FWD RX .
Great articles on octane in your links. I always felt octane over 87 was of no benefit whatsoever for the RX. The article not only supports this theory but also makes reference to higher than necessary octane being harmful, causing your engine to become an "octane junkie".

LexRX

Exactly. I learned that fact for the first time reading the article, ironic really - the fact that using a higher octane than necessary is not only unnecessary (and wasteful) but creates carbon deposits; at the same time, many lower compression engines (that are designed for 87 octane) need a higher octane fuel to stop the pinging.

Da Hapa, I hope that helps answer your question, or make your decision.

Da Hapa

It does.

thanks to everyone for their input.

kRonX

iTrader: (1)

I also have a question concerning the type of octane im suppose to put in my rx300. Since i bought the car in 2002 i always used medium grade (89). And just about a month ago, when i tried to start my engine, it would start right up but would die immediately, wouldnt idle unless i pressed the gas pedal and hold it. This happened like 5 times in one month. So I took it to the dealer, and the guys asked me what type of gas im putting into the car and told them 89. Then they told me that it is not idleing because im not putting in the highest octane gas (91). Therefore causing the idle control valve to not work properly... They replaced everything and now im using 91. Its been about a month and no idleing problem. So im wondering is it really the type of gas i put in my car or is there something else that causes this idleing problem?

jcg

Not only are people stating milage and not specifying AWD or FWD they don't say if they took the reading off the trip computer or figured it out themselves.

My trip computer reading has never been closer than 1 1/2 miles per gal when figuring it myself.

Computer is always on the high side.