sendsley

What type of gas is recommended in the RX330?

What are you using? Has anyone done a test of different octanes and seen a difference?

One of the reasons I ask is because as I await my new RX330 the MPG will certainly be less than my sports car ....... but my sports car requires premium gas so if I can use lower octance gas this will balance out the drop in MPG.


Thanks!

Scott
www.ScottsPicks.com

ederny

The bottom line is:

• The RX 300/330 engines are designed for regular gas (87 Octane).
• You will not get higher milage with higher octane.
• Although the engines are reasonably high compression, they use knock sensors to cut back performance by retarding spark, etc. when under heavy load accelerating & WOT)
• Premium gas comes into play at WOT (wide open throttle), like when passing, hill climb, accelerating, towing (i.e you may see a little more performance at high output levels).

You can find discussions about Octane here. Select item #4 under General.

CK6Speed

iTrader: (1)

Anyone have the 330 manual on hand? My wife has the car so I can't view it right now, but I read in the 330 manual that the engine was designed to run on #91. However, every car I've had that required premium fuel, it would say so on the instrument cluster near the gas gauge and the 330 does not say so. So far I've filled up twice with Premium since there are places where we can get it for $2.07. Most places are around $2.14 right now. Eitherway, its not that much more expensive and I rather not have the knock sensors retard the ignition timing. We have been getting about 20-21MPG thus far. In comparion, my NSX gets about 21MPG and my old 2.5L BMW used to get about 22MPG. My 3.2L Legend used to get about 20MPG as well. All my driving is about 60% city and 40% highway. I know the MPG will go up when we move later this year and it will flip flop the city/highway ratio.

smalcom

The manual for the RX330 actually recommends 87 octane (Research Octane 91). Am using regular (87 octane) with no adverse effects.

LexRX

This topic comes up often. I say, it it doesn't explicitly say to use premium only, then use what you want. If you want regular, use regular; you're paying for it.

I know the RX300 manual states that premium fuel is recommended. The RX300's engine has a fairly high compression ratio of 10.5:1 so using premium fuel isn't fatuous. I use premium gas on every fill up, no regrets.

CK6Speed

iTrader: (1)

Ahh, I knew I saw 91 somewhere. I didn't realize there was a difference between Research octane and what they post on the pump.

Skip

My first tank was filled with 87. Car would nose over on shifts and heavy throttle position. Second tank was filled with 91. No more nosing over. I am sure that it was the knock sensors telling the computer to pull some timing that was causing the nose over. I will probably run 91 as it is cheap insurance against detonation. My 330 runs better on 91 than 87. I did not say that it is faster, just that it runs smoother. Skip

CK6Speed

iTrader: (1)

For anyone who is interested, this is exactly what is printed in the manual.

"Select Octane Rating 87 (Research Octane Number 91) or higher. For improved vehicle performance, the use of premium unleaded gasoline with an Octane Rating of 91 (Research Octane Number96) or higher is recomended."

My take is 87 is the minimum they recomend and can be used since the vehicle is equiped with "Knock Sensors" and will retard timing. However, Premium would probably be a better choice as to avoid knock all together if possible. I get this from the statement in the manual where it says...

"However, occasionally, you may notice light knocking for a short time while accelerating or drving up hills. This is normal and there is no need for concern."

I rather avoid this as much as possible, and if it can happen with the recomended premium fuel, I figure it would happen more often with 87 octane fuel. Anyone else have any input?

JRB

One other option of course is mid-grade (89 or 90) - would save a little money and also minimize any knocking.

lexuslover

i've been using 89 octane (mid-grade in So Cal) and i think the car is driving fine. i tried two tanks of premium 91 octane, and didn't notice much of a difference. i also used 89 octane in my old RX300 ('01), and never noticed anything bad.

i don't understand the mechanics of the whole gas issue - can someone explain what "knocking" is and what compression ratios have to do with gas selection?

also Skip - what do you mean that your car is "nosing over"?

seems like there's some conflicting info in this post. so what's the bottom line? is using 87 or 89 as opposed to 91 or 93 octane going to HARM your car, or cause it to drive funny, or nothing at all?? i've only used premium fuel in cars where it says it's required (like on the dash or on the gas cap door)

LexRX

lexuslover, simply put, using regular fuel (87 octane) will not hurt your engine. Take a look at a couple of explanations I found, and can agree with. I hope this begins to clear things up for you.

-----------------------------------------------------------------------------------------------------

First, a an explanation from another message board:
http://member.rivernet.com.au/btaylo...uelOctane.html

-----------------------------------------------------------------------------------------------------

Second, a good Q&A:
Q: Will my car benefit from octane boosting?
A: Consumer organizations have effectively emphasized the larger markups that oil companies charge for high octane gasoline, implying that for most vehicles higher octane fuel is a complete waste of money. It has been quite a long time since the consumer alert was issued. Since then engine technology has evolved greatly, while people's perceptions generally have not.

Modern vehicles now use computerized engine management systems that can react to engine knock and retard ignition timing if low octane fuel is being used. Consequently cars are now being manufactured with very high compression ratios that appear to give good fuel economy and at the same time good performance. This combination does assume that fuel of adequate octane is being used.

Q: Why bother to boost octane at all since my engine can run just fine on lower octane fuel?

A: For a high compression engine to run on low octane fuel, the engine management system will need to retard the ignition timing to prevent preignition or pinging. Retarding the ignition timing means that the firing of the spark plug is delayed until a later moment in the compression stroke. It does not take much to see that a later onset of combustion means that the combustion is less complete, which in turn mean less power and poorer fuel economy. It is possible that the casual driver will still come out ahead in terms of saving money by using low octane fuel, but the retarded ignition advance also means a rougher running engine and a much duller throttle response. Thus octane boosting is not necessarily of interest to all motorists but rather the enthusiasts.

For turbocharged or supercharged engines, insufficient octane will also lead the engine management system to curtail the amount of boost which in turn defeats the purpose of these engines.

-----------------------------------------------------------------------------------------------------

ederny

...keep in mind, that ping (knock) is a function of how fast the fuel/air burns when it is ignited during the compression stroke and most importantly, the amount of charge (read as how far open the throttle is).

That is, at idle you generally don't get knock, but at WOT with a lot of mixture going into the combustion chamber, the pressure from the burn (explosion) is much higher contributing to knock or pounding of the piston top, often as the piston is still trying to compress the the burning mix (normal spark timing is generally before TDC (Top Dead Center).

Higher octane slows the burning (the flame front going out from the spark).

However, I would take exception with the retarded spark causing incomplete burn and therefore less power. Rather, delayed spark causes latter burn where the pressure maxium (power) happens as the piston is on it way down and therefore less force and mechanical advantage applied to the crank shaft. Be it as it may, retarding = less power, noticable at high output or WOT.

LexRX

I think this, in a nutshell, is why Lexus recommends 91 octane.

Skip

What I meant ,is the car feels like you take your foot off the gas, for a split second, then get back on the gas. What is happening is that the knock sensors hear some pinging and the computer pulls some spark advance out till it doesn't hear it any longer. The reason that it happens on the shifts and high throttle position is that there is more load on the engine during these times. I drove my 330 to Big Bear and back today and it is really a great driver. I have the performance package and I just set the ride height to low and it handles the mountain roads great. Much better than the 2001 Denali that it replaced. The auto stick shifter is really nice on twisty mountain roads. I hardly changed throttle position going up the hill but I shifted it more times than I care to admit. Going down the hill I used the shifter instead of brakes and that worked neat also. I think that I am going to really like this car ! I just wish that they would get the trailer hitch out before summer is over. Skip

lexuslover

thanks for the quick replies! hmmm, i wish i had the perf pkg to test out the shifter too.

oh well, i guess i will try a few more tanks of premium to see if i notice anything better this time. i'm already at 2100 miles, so i have a good feel for the car, but i see what you mean about "nosing over" now. maybe premium octane will help improve the gear changes.

the gear changes have been a little rough sometimes, usually in the morning when the car is just getting warmed up. also a little sluggish IMO. but perhaps the 91 octane will give it a little more smoothness and a lot more "umph". i guess i'm just spoiled by the smooth Lexus V8 in the GS430 . . .