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With the rising costs of gasoline lately...more and more questions are being asked about gas. Why do we have to use premium? What can I do to save gas? Where can you buy the best gas? So, if you have questions about gasoline or why your MPG sucks, post 'em here.

What is the real MPG for my car?
Find a Car

What is the best BRAND of gasoline to put in my car? Some would say TOP-TIER FUELS. For more information or to find who is a TOP-TIER retailer click below.
Top Tier Gasoline

The Lexus Manual says that "Premium Gasoline is REQUIRED"....not reccomended....but can I put in Regular gas? Some great information can be found here.
Your Car is a Temple, so Put in the Good Stuff. - Column/Larry Webster/C/D Staff/Columns/Features/Car and Driver - Car And Driver
The short answer is yes. The car will run fine with 87 octane. However, if used over a long period of time, your risks are: Decresed MPG, Decreased Performance, Possible Engine Knock and potential damage to your engine.

Here is a study from Car and Driver about the performance difference between Regular and Premium.
Regular or Premium? - Feature/Features/Classic Cars/High Performance/Hot Lists/Reviews/Car and Driver - Car And Driver
Basically for most cars if the car can use regular unleaded, you probably won't see much of a difference to add premium. Some cars might even lose power. However, if your car REQUIRES (not Reccomends) 91 octane or Premium, then you will lose power and have a potential knock problem. You're "seat of the pants" might not be able to tell the performance difference as it might only be 2-5hp. But anyone who has driven an IS300 knows....we need all the power we can get.


I will add to this list/thread as I have time.
 

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nice post. Top Tier Gasoline link was interesting. i always used mobil for years until i had no choice but to stop at a shell station because i needed gas. i was able to feel a difference in performance. i have switched back and forth between mobil and shell and i now use shell every time i can.
 

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Hello, everyone my name is Mike and I'am new to this forum. I own an '01 black IS 300 which I purchased a couple of weeks ago. I have a question....Will putting 89 hurt? I know many people with an IS use 89 and it's just one step lower then premium, has anyone here experienced problems while using an octane rating of 89 for a long period of time? I've had my car for a month and so far so good.. lol
 

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Hello, everyone my name is Mike and I'am new to this forum. I own an '01 black IS 300 which I purchased a couple of weeks ago. I have a question....Will putting 89 hurt? I know many people with an IS use 89 and it's just one step lower then premium, has anyone here experienced problems while using an octane rating of 89 for a long period of time? I've had my car for a month and so far so good.. lol
use search and 91+ octane. If you can't afford $1.50 more a tank, go pick up an econobox that uses 87 octane..
 

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I could get 91, I just wanted to know I usually pump gas at a bp or shell and I wanted to know if I use 89 for a long period of time will hurt my car if I get gas at a top gas station
 

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I was told by the dealer that my car requires 94 octane I had been using 91 before that but I use 94 now. Which is only available at Sunoco here in Canada. It’s not the price I'm worried about it’s only a $5 difference per tank but the question is do I really require 94 or is 91 just as fine.

I drive a 06 IS 250 AWD

Also the car starts going crazy with the AVG Tank MPG after i fill up I'm not sure which reading I'm suppose to look at.
 

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hmmm...not sure...93 is the highest we have here. actually didnt see this thread before. but describe how it goes crazy? once i got my car i just put in shell v-power all the time, with my old ride i just put whatever was the cheapest.
 

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by crazy i mean it starts to go up and down..like its not stable goes from 8.0MPG and keeps rising to 30.4 MPG then back down to 24 MPG and usually stops around 19-21 MPG
 

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by crazy i mean it starts to go up and down..like its not stable goes from 8.0MPG and keeps rising to 30.4 MPG then back down to 24 MPG and usually stops around 19-21 MPG
Yes, I've noticed this too. I hope I'm not misunderstanding you and giving you a silly response or something, but this is my understanding so far:

1.) When you re-fill your car, obviously the Tank AVG will be reset to 0,

2.) When you first start driving, you'll be generally in lower gear, accelerating more, etc. thus using more fuel than coasting/driving on a highway and such. This would probably be why you see 8 mpg,

3.) Once you hop on to the interstate/highway or even just a street where you don't stop much, you'll see your mpg shoot up to 30 (I've even gotten mine up to 37 straight up on the highway going at around 55 mph about 5 mins after I filled up the tank),

4.) Then as you average out your city/highway driving your mpg will pop back down to normal or estimated mpgs.

It's your simple mathematics principle of averages... which is why your mpgs fluctuate much less near the end of your fuel tank and settle to your actual average value.

Anyway, I apologize if I misunderstood you and am over-analyzing what you wanted for an answer; but I just wanted to make sure I tried to answer your question.

Good luck with your mpgs!!!

-kbkura

P.S. I pour 93 octane gas in my car... nothing but the best for a Lexus!!! There's a Shell near my house, but Chevron is much cheaper (although no V-Power...), so I usually go there...
 

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Hello, everyone my name is Mike and I'am new to this forum. I own an '01 black IS 300 which I purchased a couple of weeks ago. I have a question....Will putting 89 hurt? I know many people with an IS use 89 and it's just one step lower then premium, has anyone here experienced problems while using an octane rating of 89 for a long period of time? I've had my car for a month and so far so good.. lol
No I haven't. I think most people follow it as a safety precaution because we all LOVE our IS. However I might be one of those very few who are willing to take a risk with the LOVE OF THEIR LIVES.
 

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Discussion Starter #15
Hello, everyone my name is Mike and I'am new to this forum. I own an '01 black IS 300 which I purchased a couple of weeks ago. I have a question....Will putting 89 hurt? I know many people with an IS use 89 and it's just one step lower then premium, has anyone here experienced problems while using an octane rating of 89 for a long period of time? I've had my car for a month and so far so good.. lol
The Lexus Manual says that "Premium Gasoline is REQUIRED"....not reccomended....but can I put in Regular gas? Some great information can be found here.
Your Car is a Temple, so Put in the Good Stuff. - Column/Larry Webster/C/D Staff/Columns/Features/Car and Driver - Car And Driver
The short answer is yes. The car will run fine with 87 octane. However, if used over a long period of time, your risks are: Decresed MPG, Decreased Performance, Possible Engine Knock and potential damage to your engine.

Here is a study from Car and Driver about the performance difference between Regular and Premium.
Regular or Premium? - Feature/Features/Classic Cars/High Performance/Hot Lists/Reviews/Car and Driver - Car And Driver
Basically for most cars if the car can use regular unleaded, you probably won't see much of a difference to add premium. Some cars might even lose power. However, if your car REQUIRES (not Reccomends) 91 octane or Premium, then you will lose power and have a potential knock problem. You're "seat of the pants" might not be able to tell the performance difference as it might only be 2-5hp. But anyone who has driven an IS300 knows....we need all the power we can get.
Read the first post of this thread?
 

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Ummm I'm new here, but I was wondering what does it mean that it has "a potential knock problem?" The reason is that my car is making some weird noise lately and it sounds like it's from the back. Any advice? Sorry I'm a noobie :D
 

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Ummm I'm new here, but I was wondering what does it mean that it has "a potential knock problem?" The reason is that my car is making some weird noise lately and it sounds like it's from the back. Any advice? Sorry I'm a noobie :D
knocking happens when the combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The peak of the combustion process no longer occurs at the optimum moment and the shock wave creates the characteristic metallic knocking sound, and cylinder pressure increases dramatically. So when you use a lower octane gas, knocking happens...but because modern cars like ours have sensors that detect mixture levels the ECU reprograms to prevent knocking. So by using lower octane gas, your not doing any harm to the engine but it wont perform at its optimum peak, even head techs at Acura say they alternate between low and high octane gas, which is the best way to go...your weird noise is probably something in your trunk, check your spare tire and stuff, if its not, then have your car looked at
 

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knocking happens when the combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The peak of the combustion process no longer occurs at the optimum moment and the shock wave creates the characteristic metallic knocking sound, and cylinder pressure increases dramatically. So when you use a lower octane gas, knocking happens...
So far so good...

but because modern cars like ours have sensors that detect mixture levels the ECU reprograms to prevent knocking. So by using lower octane gas, your not doing any harm to the engine but it wont perform at its optimum peak, even head techs at Acura say they alternate between low and high octane gas, which is the best way to go...your weird noise is probably something in your trunk, check your spare tire and stuff, if its not, then have your car looked at

And here it falls apart.

Your ECU has no idea what "mixture" of fuel the car has in it.

knock sensors don't detect fuel octane...if they did they'd be named octane sensors.

They detect knock

So you've already damaged your engine (very, very slightly) when they detect knock happening.

Because they can sense it so quickly, and report it to the ECU, the ECU can pull timing from the engine to stop it, also quickly, hence why you do only very very slight damage.


What happens next though?

The ECU is still programed for the timing/octane it came from the factory for.

So over time it'll add that timing back, figuring the knock was an abberation.

Then the car will knock again, doing very very tiny amounts of harm, again.

Then the sensors will notice, tell the ECU, and the ECU will pull timing again.

Repeat ad naseum.

So you probably COULD safely drive a car programmed for 91 octane on 87, and let the ECU and sensors keep doing this, for 50,000 miles.

but if you tore the motor down it'd look like it had 150,000 on it.

(Engines being as reliable as they are these days it might well still have lots of life left even then though).

But don't for a moment think you're not doing any harm running lower octane than your engine requires, even once.
 

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I always use 91 octane as that is the best grade of fuel we have around here. I do have a buddy that uses 87 octane on his car and whenever he shuts it off the car shakes a little bit. I am pretty sure this is because he uses crappy gas, but I was wondering if it could be any other type of problem.
 
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