The Great Oil Change Discussion

[seohenning]

I am just wondering if anyone has religiously been using a lower grade than 93 octane in their IS250/350 and if they have noticed a difference in gas mileage/performance and or noticed any problems?

I have heard that you can use as low as 87 without any problems however I have also heard the opposite and the dealer states that the car might make some knocking noise's w/ lower octane.

It is understandable that you might get worse mileage with lower the octane but I was wondering if anyone has tried and had good enough gas mileage to make paying less worth it?

[bartkat]

I am just wondering if anyone has religiously been using a lower grade than 93 octane in their IS250/350 and if they have noticed a difference in gas mileage/performance and or noticed any problems?

I have heard that you can use as low as 87 without any problems however I have also heard the opposite and the dealer states that the car might make some knocking noise's w/ lower octane.

It is understandable that you might get worse mileage with lower the octane but I was wondering if anyone has tried and had good enough gas mileage to make paying less worth it?

It's not a good idea. Simply use premium gas and you won't have to worry about any of the problems. This has been concluded here several times before. There are plenty of threads on this topic already.

[bejoseph]

I thought I remembered that some panel had to be removed for an oil change, thanks.

The price definitely sounds much better if a loaner is included. I wonder if this is what separates the cheaper dealers from the pricier ones.

My father did have them inspect a few things, found nothing wrong. But that might be why he got a loaner. I don't know if his dealer (in Va. Beach VA) would include a loaner for just an oil change.

I doubt they would for an oil change, but they will for a minor service (the maintenance schedule calls for minor services every 5k miles).

Oil filter access panel is on drivers side right behind radiator accesed under the car. There are 3 10mm screws and the filter is right there, use a 63mm filter cap wrench to remove.

[larry chester]

I am also interested in finding out whether you have noticed any difference if you switched between Premium and Mid-Grade. I have used Premium and Mid-Grade, but since I don't push my car all out all the time, I don't know that it really matters. If I buy Premium, I feel that I am just spending $.10 per gallon for nothing.

Comments??

larry

[bartkat]

Using less than 91 octane is really not a good idea. I think if Lexus thought you could use regular gas on a ruotine basis they wouldn't have specified premium.

http://us.lexusownersclub.com/forums/index...;hl=premium+gas

[sjg86]

My salesman told me not to waste money on premium. He said mid-grade was perfectly fine, and he was very knowledgeable so I trust he knows that it work since its one of the biggest dealers in the east.

I just got my IS last week. I plan to rotate w/ a little premium every so often.

Has anyone had problems with mid-range?

Could there be any longterm effects/damage with this grade?

[is350ace]

My salesman told me not to waste money on premium. He said mid-grade was perfectly fine, and he was very knowledgeable so I trust he knows that it work since its one of the biggest dealers in the east.

I just got my IS last week. I plan to rotate w/ a little premium every so often.

Has anyone had problems with mid-range?

Could there be any longterm effects/damage with this grade?

I think you will be fine if you rotate with a little premium every once in a while. I wouldn't drop to regular though. As for me with the 350, my car will see nothing but premium. It great having 93 octane here in GA.

[larry chester]

I've been using midgrade since I purchased my IS250. I wouldn't drop to regular, because there may be some pinging or knocking that you don't hear. Any of that nonsense could result in damage to your engine which is not worth the savings.

But to mid-grade? Not sure that it's a bad option. I ran midgrade on my SC300, and it now has 210K on it.

Hmmmm Hey, what's a couple of octane points here or there?

On the other hand, look at the economics. Premium costs $.10 per gallon more than mid-grade. You put 20,000 miles on your car every year. You get roughly 22 miles per gallon. That means that you are using 909 gallons per year. Using a Mid-Grade will save you $90 per year. I'm all for saving a couple of bucks, but if it really made a difference in the way the car performed, I wouldn't do it.

larry

[warhummer1]

My salesman told me not to waste money on premium. He said mid-grade was perfectly fine, and he was very knowledgeable so I trust he knows that it work since its one of the biggest dealers in the east.

I just got my IS last week. I plan to rotate w/ a little premium every so often.

Has anyone had problems with mid-range?

Could there be any longterm effects/damage with this grade?

From an engineering standpoint, premium gasoline is specified due to the high compression ratio of the engine. Basically, the fuel/air mixture is "squashed" more as compared to a lower compression ratio engine. At higher compression ratios, the fuel has a tendency to spontaneously ignite, without the benefit of the spark from the spark plug. When this happens at any point other than top dead center (piston is at the absolute highest point of its travel), the engine will not be able to perform at its best.

The engine computer can help mitigate some of this but bottom line is that engine knock is bad. Think of it this way: if one was to go up to an engine and manually turn the crankshaft, you would see all the cylinders move up and down at different times, but all in some sort of synchronous motion. Proper ignition of the fuel/air mixture forces the pistons downward in their cylinders to turn the crankshaft. When this ignition happens prematurely (say from a lower octane fuel), you now have an explosive force trying to push downward on a piston that is supposed to traveling upwards, reducing power and introducing stresses within the engine that should not be there.

Could one get away with mixing gas? I would say in most situations where you're not max-performing the engine (think steady highway cruising) then any damage would be minimized. However, heavy acceleration, stop-and go traffic situations are cases where I would not skimp on the required fuel. It's good insurance if you plan on keeping the car.

Now sticking premium gas in a car that doesn't require it is, in my opinion, a waste of money. There might be some subtle difference in detergent additives among the different grades (company depending), but that's about it. One situation where this would not be the case is an older car that knocks or pings under acceleration. You can mitigate this with a higher octane gasoline.

So, after much rambling, if the owners manual says you need 91 octane or higher fuel, you need 91 octane or higher fuel. Regardless of what you hear some schmo say on the internet. ;)

[rhsmd]

what about the octane grade at high altitutes.

i live in denver.

in my acura tl i've used all three grades, and have never,ever noticed knock or other problems.

my dad always felt that it was all the same gas. anyway, i've heard that the grade needs change at altitude.

[lexus411]

Directly from the Lexus engineers.. 91 octane or better must be used because of the Dual Direct injection. Sorry iof the was mentioned above

[mdsbrain]

I have about 1k miles on my 07 IS250 AWD and the last few tanks have been regular 87 octane. I put in 93 for the first few hundred miles and since then its been running the cheap stuff with no ill effects on performance or gas mileage.

If the car is under warranty during the time I own it then it will run the cheap stuff unless they can claim my cheap gas causes a problem. But I am also a person who runs that fuel system cleaner treatments in my car. For what its worth...

[bartkat]

It might end up with you doing the proving. Run what you want to run. It's your $35 to 45,000 car. :chairshot: :chairshot:

[sjg86]

I've been using midgrade since I purchased my IS250. I wouldn't drop to regular, because there may be some pinging or knocking that you don't hear. Any of that nonsense could result in damage to your engine which is not worth the savings.

But to mid-grade? Not sure that it's a bad option. I ran midgrade on my SC300, and it now has 210K on it.

Hmmmm Hey, what's a couple of octane points here or there?

On the other hand, look at the economics. Premium costs $.10 per gallon more than mid-grade. You put 20,000 miles on your car every year. You get roughly 22 miles per gallon. That means that you are using 909 gallons per year. Using a Mid-Grade will save you $90 per year. I'm all for saving a couple of bucks, but if it really made a difference in the way the car performed, I wouldn't do it.

larry

Wow I never looked at it that way. I'd rather spend the extra $50 or so and feel secure.

[larry chester]

If the car is under warranty during the time I own it then it will run the cheap stuff unless they can claim my cheap gas causes a problem. But I am also a person who runs that fuel system cleaner treatments in my car. For what its worth...

Brain(?):

Don't kid yourself. Here's the scenario. You come into the dealership, under warranty, with a car that traditionally has ZERO problems running hi-test fuel for the 70K miles of the warranty, and you're having trouble. So they take a look at the engine. Compression is around 75 psi, and the only way that would occur is from bad valves or bad rings. The valves are most suspect.

So they tell you that they'll take a look, but the only way that this car goes through valves is if you don't use Premium gas. So they ask "have you used Premium Gas?" Now, whatcha gonna say, because they will know for a certainty when they open up that engine.

And then they'll give you the bill for the $6 - $7K that they'll charge for a set of valves and rings to bring the engine up to spec. Or else, you'll just drive your poor car home, limping with your tail between your legs. And all because you wouldn't pony up the extra $3.50 per tank. But you'll put in some gas additive every few tankfuls in your car for roughly the same amount of money.

Go figger. I sure can't. But like Bart said -- It's yer car, you can do what you want.

larry

[warhummer1]

If the car is under warranty during the time I own it then it will run the cheap stuff unless they can claim my cheap gas causes a problem. But I am also a person who runs that fuel system cleaner treatments in my car. For what its worth...

Brain(?):

Don't kid yourself. Here's the scenario. You come into the dealership, under warranty, with a car that traditionally has ZERO problems running hi-test fuel for the 70K miles of the warranty, and you're having trouble. So they take a look at the engine. Compression is around 75 psi, and the only way that would occur is from bad valves or bad rings. The valves are most suspect.

So they tell you that they'll take a look, but the only way that this car goes through valves is if you don't use Premium gas. So they ask "have you used Premium Gas?" Now, whatcha gonna say, because they will know for a certainty when they open up that engine.

And then they'll give you the bill for the $6 - $7K that they'll charge for a set of valves and rings to bring the engine up to spec. Or else, you'll just drive your poor car home, limping with your tail between your legs. And all because you wouldn't pony up the extra $3.50 per tank. But you'll put in some gas additive every few tankfuls in your car for roughly the same amount of money.

Go figger. I sure can't. But like Bart said -- It's yer car, you can do what you want.

larry

Buy a Mustang if you want to use 87 octane. :D

what about the octane grade at high altitutes.

i live in denver.

in my acura tl i've used all three grades, and have never,ever noticed knock or other problems.

my dad always felt that it was all the same gas. anyway, i've heard that the grade needs change at altitude.

Lower octane fuel can be used at higher elevations due to the lower oxygen concentration in the ambient air. That whole stoichiometric thing.

[SKperformance]

high compression engines especially with variable timing NEED higher octane to survive and run right. One or 2 gas tanks will show no difference until it completely balances . I never use low grade gas and this debate is sooooooooooo old it has so many threads and each one gets closed as there is never anything added that is new news (EVER). Just lots of guessing and hear say of i think.

Look in the general maintenance section for the octane thread.

[bartkat]

I left the thread open because as of yet we have not had an extended discussion on gasoline as applies to the 2nd generation IS. Many of the users here are new to Lexus and some are on their first new car. Le't leave it open awhile so later on when someone brings it up there will be something in the forum that can be searched up and referenced.

The great gas debate exists in other Lexus model forums, but we need one that's IS specific.

[chughtaijr]

Directly from the Lexus engineers.. 91 octane or better must be used because of the Dual Direct injection. Sorry iof the was mentioned above

So with my new car stuck in the blizzard I had nothing better to do except read the owners manual cover to cover, I think it is informative (and given it says so in the owners manual should be warranty safe)

Page 395

Premium unleaded gasoline with an octane rating of 91 or higher required for optimal engine performance. But... if premium is not available you may use as low as 87 octane.

On a slightly different note, it also says you may occasionally notice light knocking for a short time while accelerating or driving up a hill, This is normal and there is no need for concern.

Doesnt seem like you can go wrong following Lexus' recommendations, especially as was pointed out the cost savings is minimal over a year. Plus I bought the 350 because I wanted "Optimal engine performance"

Premium for me....

[Tango]

I think you will be fine if you rotate with a little premium every once in a while. I wouldn't drop to regular though. As for me with the 350, my car will see nothing but premium. It great having 93 octane here in GA.

In the UK I use 99 octane :) available at the local supermarket, BP Ultimate or Shell Optimax (which is 98 RON and the difference is noticable over 87 RON .....gives about 10% improvement on mpg..or just use the extra power available.

BP also have 103 octane on retail at selected stations in the UK, but it's intended for race/track day fuel and performance cars need to be mapped for it. It's also priced at £2.50 a litre, (nearly $20 US per gallon).

[mdsbrain]

Directly from the Lexus engineers.. 91 octane or better must be used because of the Dual Direct injection. Sorry iof the was mentioned above

So with my new car stuck in the blizzard I had nothing better to do except read the owners manual cover to cover, I think it is informative (and given it says so in the owners manual should be warranty safe)

Page 395

Premium unleaded gasoline with an octane rating of 91 or higher required for optimal engine performance. But... if premium is not available you may use as low as 87 octane.

This is also what I read. It says for "optimal engine performance". What is the definition of this? Best power or fuel economy or life of the engine?

[bartkat]

Optimal is the best all around performance in all categories. In other words, the way the engine was designed to operate.

Definition of octane rating

Octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline, for example, has the same octane rating as a mixture of 87 vol-% isooctane and 13 vol-% n-heptane. This does not mean, however, that the gasoline actually should contain these chemicals in these proportions. It simply means that it has the same autoignition resistance as the described mixture.

A high tendency to autoignite, or low octane rating, is undesirable in a gasoline engine but desirable in a diesel engine. The standard for the combustion quality of diesel fuel is the cetane number. A diesel fuel with a high cetane number has a high tendency to autoignite, as is preferred.

[edit] Measurement methods

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-95 (regular) in Europe.

http://en.wikipedia.org/wiki/Octane_rating...urement_methods

[Roq]

I am also interested in finding out whether you have noticed any difference if you switched between Premium and Mid-Grade. I have used Premium and Mid-Grade, but since I don't push my car all out all the time, I don't know that it really matters. If I buy Premium, I feel that I am just spending $.10 per gallon for nothing.

Comments??

larry

I just wanted to bring up a little flaw in your logic here. First you pose the question of "whether YOU have noticed any difference ... between Premium and Mid-Grade [gasoline]". The whole point of premium gasoline isn't so YOU can notice a difference, it's so your CAR can. It's not magical horsepower juice, its cleaner gasoline for high quality engines. Your car isn't a lawnmower, its a lexus.

Secondly your reasoning behind not using premium on top of "not noticing a difference" is that premium costs $.10 more per gallon. I drive more then probably anyone on these forums, or at least in the top 2%. I commute 72 miles each way, 144 miles a day, 4 days per week (I work 4-10's). Just commuting to and from work that's 576 miles a week, and 29,952 miles per year. This doesn't count going out, road trips, etc.

Lets assume I get 26 miles per gallon. That's 1,153 gallons of gas I have to buy per year. The difference between Premium and Mid-Range per year totals out to $115.30. That's a small price to pay to ensure your engine is running as clean and efficiently as possible. Odds are you, and most people here, drive half of what I do, making that total closer to $60 a year.

The Bottom Line: Put premium gasoline in your IS.

[larry chester]

Roq:

There's no denying that you put a lot of miles on your car. I average about 20K per year, which puts me at 2/3 of what you drive, which is why I like a car like a Lexus. More miles per total dollar spent. But the piont of higher cost and higher grade gasoline isn't that it burns cleaner, but that it burns FASTER. That makes it better suited to the turbo engines, the high compression engines that can make use of a higher octane gasoline. Even Lexus puts their stats on the car with a footnote saying that these are if you are using Premium Gasoline, indicating that using a lower grade of gasoline will reduce performance in the car.

I am not convinced that the car won't notice the difference between Premium and Regular over a long period of time, but between Mid-grade and Premium, I'm not so sure. As I had said. I put over 200K of mid-grade fill-ups on a Lexus SC300 that was supposed to burn Premium and I haven't notice the difference in how the car starts or runs, or in the gas mileage, except what you would expect from a 200K car.

Regarding the economic differences, you haven't really read all of my posts in this thread if you think that I have missed the paltry economic differences of this.

Hey, what's a couple of octane points here or there?

On the other hand, look at the economics. Premium costs $.10 per gallon more than mid-grade. You put 20,000 miles on your car every year. You get roughly 22 miles per gallon. That means that you are using 909 gallons per year. Using a Mid-Grade will save you $90 per year. I'm all for saving a couple of bucks, but if it really made a difference in the way the car performed, I wouldn't do it.

To be honest, if it made any difference, I wouldn't do it to save the money. And my a$$ can't tell if it notices a difference, it just knows that it loves sitting in the car while it's moving. ;)

larry

[bartkat]

Premium (higher octane) gasoline burns less easily, thus less tendency to pre-ignite (knock) in higher compression engines.

The IS250 has a compression ration of 12.0:1 while the IS350 has 11.8:1. That's high compression in anybody's book.

Seeing as how Lexus went to the trouble to build these fine, relatively high performance engines, and seeing as how I paid premium dollars to obtain one of these I'm sure not gonna feed it anything less than top shelf stuff.

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Adding some key search words for this thread so it can be easily found later on.

gasoline octane premium regular gas fuel pump additives go juice timing knock knocking compression filter tank mid grade mid-grade hi test high octane performance low petrol