The manual for our Lexus LX470 recommends premium gas and that's what we've always used but it's SO expensive I've considered switching to the mid-grade. Anyone know the reason(s) behind using premium vs. mid-grade unleaded and why it would be specifically recommended in the Owner's Manual? I want to take care of this vehicle (2002 w/ 106k miles) and have been hesitant to switch since but am not sure the benefits of premium gas will outweigh the cost (~$5-$7/fill/week).....

I get better millage with the mid grade than with the lower grade.
Tried the premium and could not tell any difference.

If the compression ratio and ignition advance curve are optimized for higher octane fuel, then that's what the engine wants.

I don't know when engine management systems started to incorporate knock sensors so the computer can back off the timing. Cars thus equipped will run on lower octane fuels, the system protecting them from "knock", but the performance will be compromised, particularly under heavier load like passing, hill climbing and the like.

What that tells us is the particular engine combination needs no more octane than provided by mid grade fuel to perform at its peak.

In my base model tin can there's no advantage to going above the 87 octane base grade unleaded.

High compression engine with regular, or midgrade may knock. Usually the question is why burn premium in regular engines. With the computer timing the engine may adapt to whatever octane, but it may come at a mileage reduction from retarding the engine.

Colorado, in their wisdom has 85 octane, claiming it is equal to 87 at high altitude; I am not sure. What does Nebraska have? I know Wyoming gas is superior to Colorados.

I'm in your same class of vehicle with a bit more. Owners Manual calls for premium and I do it.

Noticed yesterday I received 20mpg on a 500 mile trip using 93oct. The last time I used 91oct I only received 18mpg.

Further, if I can I stay away from the ethanol stuff things just feel better. That's also why I drink good whisky!!

I had a 1987 model car with a small, high compression engine. Double overhead cams, fuel injection, rpm's like crazy. It needed good gas, and it's engine management system wasn't new/sophisticated enough to protect it against low octane fuel. It also had a smallish fuel tank, so while it got nearly 40 mpg highway on cruise control I still had to sometimes buy gas whenever/wherever available.

One time I got caught (out in west Texas IIRC) and the only unleaded available was some horrid 83 (yes, 83) octane motor killer. I put enough in the tank to get me to a bit larger population area and crossed my fingers. Man, did I ever have to feather the throttle to get going without knocking the engine to death. At the first decent place I could stop I dumped two bottles of octane booster in the tank and topped it off with premium.

I dont think you need premium anymore. I could very well be wrong. With E10 all over you have high octane in regular gas. Ethanol is 116 octane. E 10 should raise it at least one octane. I could very well be wrong however but I always wondered if E10 makes midgrade premium grade.

All the addition of ethanol does is allow a lower grade gas be used in the blend for 87, 89, 91 or whatever.

So no, 89 octane with ethanol in it isn't the same as 91 without.

We're pretty much 87 Octane w/ premium running 91 to 93 depending....

Altitude does affect it. Here at 4600+ feet in northern Utah, regular grade is 85. Down south in St George's 2800-foot altitude, regular is rated at 87. I'm assured it is the exact same gas.

One trick you can do is alternate grades. Refill when the tank is at half, and buy mid-grade now and premium next time. It'll save you a few bucks. Not much, but it won't harm your mileage or engine much, either.

Octane rating once was way more important than it is with currently manufactured gas engines - octane rating now seems to be a gimmick taking advantage of those who don't understand the issues. In my limited view, the stuff labeled "premium" should be that with no ethanol added - that stuff can be a mess.

The primary mechanical/chemical issue to be dealt with is pre-ignition (fuel starts to burn too soon before the piston reaches TDC) and this is where the "knocking" arrives. That is mechanical hammering on a small scale, but it will cause wear and damage over time. Seems like almost all modern computer-controlled engines - especially those with variable mechanical aspects - will easily control timing of fuel ignition as related to power output and mpg.

So - how important is high octane today for the average owner? Don't know, but am suspicious that those "premium" labels and charges don't relate to higher octane as in the past. Maybe something in there is worth the higher cost, but am thinking it is not octane-related ignition control. Am thinking that some of those premium fuel mixes might have a higher energy quotient - thus giving better mpg in general - but have no evidence there.

In older engines with owner-adjusted mechanical ignition systems, especially those built with high compression ratios - octane control can be a real factor. Do you remember tetraethyl lead (ICC)? Wish I had a gallon (careful - very poisonous).

However, with precise addition of aromatics, particularly like toluene (the perfect gasoline), one can boost octane rating in non-ethanol gas to help in such cases. But, unless you are craving big power, easier to de-tune.

A friend of mine drives a high performance car with direct injection, high compression, and supercharging. Sure, the controller will protect the engine, but it detunes it to do so.

You can buy 110 at some of the pumps in SC. Especially, around the local Friday and Saturday night tracks.

Wish we had such near here - no such luck. When I worked at Sunoco in the 1950s, in R&D we were running quality control tests on that new blend pump - it enabled the consumer to select one of about 7 octane ratings from the same pump. It selectively blended a base gas with a high octane concentrate. Their label range started at 190 (not octane rating) and the top lever was Sun 260. That might still be what they are selling near those race tracks.

Back then we built up more than one engine that needed the 260. Good old days.

The book for the old 944A Cat loader says to use the cheapest fuel that gives satisfactory performance. Now that is diesel, and it also says to change the crankcase oil oftener if a high surfer fuel is used.

I'd still use the cheapest gas/fuel, that gives satisfactory performance. Check mileage each way, and do the math.

I had a Toyota Sequoia with the same 4.7 liter V8 engine and it required regular unleaded.

Your cars computer is set to run whatever octane rating is stated in the owners manual. Put anything else in the tank and the computer will adjust out the difference. You gain nothing but a higher fuel bill. In the case of the Lexus I would expect performance to suffer as the computer will adjust fuel and spark timing to prevent pre-ignition.

That's correct. Many years ago I worked for an Acura dealership and all cars called for 91 octane. But I sold one to an Air Force pilot, who said he had run the calculations and that 85 octane would work great at altitude and it was unnecessary.

We run 93 octane in my wife's supercharged Audi crossover and her Porsche Boxster as recommended and they run just fine. I run the same in my '73 Cleveland powered Mach 1 and it is fine. My Tundra sees 87 octane and it is fine. All with ethanol. I will leave it at that.

Just avoid anything with ethanol Jeff and you'll be fine. As you know I'm in the petroleum equipment business and this ethanol push here in the midwest is pure bull$hit! The state and the ethanol board are throwing big money at these station owners and the ones that are falling for it are going to be sorry after they do.

Mike

Thanks for all the input!

BTW, I agree with you on the Ethanol Mike. The folks running that industry really know how to lobby....

Our 92 Legend said to use 91 octane...but running 87 it ran fine... one really only noticed a difference if you really were trying to run it hard... the computer detuned the engine on 87... the car didn't get run hard.....

wife drove it, she got 22 mpg... I drove it and it got 28 mpg...women are harder on the gas pedal...


something else mentioned here, ( by Rocky Raab) was 85 octane fuel in Utah.... when I travel east on I 80, that is what plenty of places pump in East Nevada and across most of Wyoming... or you can buy 91 octane at a much higher price...

Going across in my Honda Pilot, I get 22 mpg around town, and 24 to 26 on the freeway.... when I have to run 85 octane, it drops down to a flat 16 mpg... and noticeably less power and responsive to the accelerator pedal.....

however, putting in some additive, that someone on the campfire mentioned a year or more ago, bounces the power and fuel mileage right back up to normal.... carried at all truck stops and most fuel station... costs me $1 to $1.25 to add to each tank...

Nice vehicles all - and good that the eth fuel works so well in them. But, I would be sure to keep running it through and not store or let any sit very long without a good additive - aging eth can make a mess. How is the cam/valve train on that Boxster holding up?

My Hemi manual says for best performance run 93 or high , ans 93 with no ethanol gets about 2MPG better mileage and lots more pulling power.Ethanol sucks unless a motor was specifcally made for ethanol ,even than do not store more gas than needed cause the ethanol will gum varnish and [bleep] every thing up

Zero issues. It is a 2010.

The obvious and cost effective thing is to buy the lower octane gas and add an octane booster. Last I priced it you could get an 18 gallon treatment of STP octane booster for $1.29. Around here its $0.38 a gallon more for premium gas. Do the math 18x0.38=6.84.

An old buddy that delivers gas to stations says to NEVER buy mid grade. He says it's a complete rip off.

Octane booster is a scam. When STP says it raises the octane 2 points that doesn't mean it makes 87 octane into 89.

The octane booster will turn 87 into 87.2

Exactly, modern computer controlled engines will burn anything without damage, however the computer will detune the engine to allow it to run the lower octane fuel and your mileage will suffer. So you're really not saving anything by running lower octane fuel because you're burning more of it.

I pretty much just go with what the owners manual calls for unless it's knocking then I go higher. Most newer engines control the knocking but I was riding I a fairly new Nissan Maxima about 6 years ago and I could hear knocking every time it accelerated. I asked the driver what fuel she ran and she said whatever was cheapest. I then pulled the owners manual out and it clearly said premium only. It was definitely newer than a 2000 model and had a fairly high compression ratio V6.

I run ethanol free premium in my small engines but think it's a waste of cash in my vehicles.

Bb

This. My 2002 Crown Vic gets good mileage on mid grade but lacks performance. The mileage does not change with premium but when I step on the gas "stuff" happens.

kwg

Energy quotient.

you get the most power from the LOWEST octane gasoline that you can run without pre-ignition.

Use what it calls for, save your self some grief or get a vehicle that calls for unleaded.

Your gas stations only receive 2 grades of gas - premium and regular. Mid grade pulls (supposedly) equal portions from each tank for a blend.

I only buy low grade for my Chevy Malibu. Shell = 28~29 mpg. Any other brand = 31~32 mpg.

actually , I would suggest you try a couple of tanks of E30 , if it is available in Omaha .

that will get you a high octane rating at what should be a cheaper price

dont swallow the idea that higher ethanol blends will hurt your engine....I have been running E30 in a 2001 non flex fuel Durango for well over 100 K miles , the vehicle is nearing 220K and still runs excellent


as far as lobbying , ethanol has a good way to go to catch up with Big Oil.....

Around here even E10 screws up the little passages on fuel injectors and lawnmower carbs. There are 2 places in all of Denver metro where you can sometimes get E0, in a gas can but not in a car. I missed both times I went out of my way to find it so the lawnmower is still on regular stuff.

I couldn't POSSIBLY agree more!!


I refuse to buy any gas that has ethanol in it.. Luckily, we have several stations that offer 91 octane gas w/o ethanol - and that's the ONLY gas I buy..

Ethanol lowers mileage and increases cost of food and fuel at the same time...

Ok,onto the question, I don't regard Lexus as cheap vehicles.

Worrying about cost of premium after buying a Lexus boggles my mind.

But the question is fuel grades... I forgot and put low octane in my airboat one weekend a while back. It dieseled all day long. The next day the oil pressure line snapped and locked the engine before I could catch it.

It was only an engine valued at about 11K to replace....

YMMV

If Al Gore wasn't into climate and instead he sold gasoline, he'd sell ethanol fuels. A huge con game "fueled" by lobbyists.

Use what your vehicle owner manual recommends and don't let your next door neighbor or a stranger on the internet decide what is best for your particular car. Same with engine oils. Many newer cars that are designed for modern blended oils for longer life get nothing but a diet of regular oil with super cheap and inefficient oil filters at cheap change locations. Engine life suffers.

I know for a fact that with a 7.0 L Camaro, anything less than 93 octane which I have to buy in some higher elevations (where sometimes only 87 or 91 are available) retards ignition and definitely affects overall performance. I had a 400+ mile weekend trip this past weekend and averaged 22.7 miles per gallon on 93 octane with both freeway and city driving, and I didn't baby the speed for an MPG rating.

Why would you want to baby it if you bought a higher performance car? And running it on cheaper gas is definitely not doing the engine any good. Again, use what the car was designed for in both gasoline and oils and you'll save money in the long run.

It may run fine, but you WILL NOT get the fuel economy from the higher ethanol blends. They are nothing but a rip off and put just as much crap in the air as straight gas.

I burn the e-10 in my vehicles, but I will not go any higher than that.

Nothing but pure gas in my chainsaws, mowers, etc.

I get the same mileage with E30 in the Durango as I ever got with E10 . The University of Mn has run some tests with different vehicles and found that a blend from E30 to E20 was optimum for fuel mileage with many rigs

I have a GS 350 and fill it with the cheap stuff without complication. I am also at 1000' elevation, so take that into consideration. I've had one Lexus or another since 1992. I've fed them 92 octane and 87 octane. I run them for 160,000 and they run better when I turn them in than when new. Very well build and engineered autos.

Like others have pointed out, the fuel computer will adjust. If you notice a performance difference with 87 or 89, then you have the anser and need the good stuff. Otherwise, save the cash.

Excepting the fact that I've NEVER gotten as good a mileage out of ethanol blended fuels as with non.

AND the fact that ethanol is hygroscopic (i.e., attracts water) and will, at some point, screw up whatever it's in..

No thankee...

Search web for non alcohol gas.....
Lots of stations out there.
But, I drive a pre def diesel.....

In general, higher octane gasoline burns cleaner than lower octane gasoline so the automobile manufacturers have an interest in recommending the higher octane fuels so they can claim lower overall fleet air pollution emissions.

Disclaimer: I work for a company that licenses petroleum refining technologies so I have an interest in ever higher octane standards. However, I DO NOT speak for my employer about this or any other issue. I only write my personal opinions.

Oh, and my wife and I only burn regular gasoline in both Lexus cars we own.

Pure gas, without ethanol, will give you better mileage, regardless of the octane. This has been my experience with a number of different vehicles.

I used to be a gasoline blender, though it was before ethanol got introduced to the mix. The octane of the gas you buy will meet the posted specifications on the pump, but you can bet it won't exceed the spec. And Uncle Sam watches real close, so if you sell an 87 R+M/2 octane gas, it had better meet that spec. You never know when they'll pull a sample and test it. They are not forgiving people. Over the years I suppose I blended billions of gallons of gasoline, and we tested every batch and had a test certification issued by an independent testing firm. I was scared of messing up and having the Feds on me.

Gasoline is made up of an assortment of blend components, and for me it was what I had on hand that would blend up to the spec. If I needed more octane, I'd buy the volume of higher octane that I needed. It's not just octane that you blend for. There are distillation curve temperatures to meet, and a vapor pressure. Alcohol gives decent octane, but has a low midpoint, which has to be compensated for by one of the other blendstocks. What I believe, but can't prove (these days) is that today's ethanol gasoline has a lower BTU content than non-oxygenated gasoline. That would lead to lower mileage.

Also of note is that I had to blend for the region where the gasoline was going. Each region does not have the same specification requirements (octane and RVP, for instance). And there were seasonal variations to meet.

As for what to run in your car or truck, you would be wise to run the fuel/octane that the manufacturer suggests.

The power of gasoline and Ethanol is rated by BTU, Gasoline contains 114,500 btu's per gallon, Ethanol (E100) contains 76,100 btu's per gallon.

Anytime you add ethanol to gasoline you reduce it's power. Gasoline is a far better choice for Engines than ethanol is by far.

The .gov demands better mileage out of car manufacturers and they reduce the efficiency of gasoline at the same time. Fuqking dunces is what they are.


For you guys that can't get ethanol free fuel for your small engines use a product called Ethanol Shield, Add this to your E10 at the rate of 1 ounce to five gallons and you will have no worries.

My daughter's 1998 Nissan Pathfinder with 180K on the clock runs decidedly better on 87 without ethanol than either 87 or 91 with ethanol. My daughter was complaining about the higher cost of fuel, 'cause Sam's Club is selling 87 with ethanol for $1.919 per gallon, but they don't sell any non-ethanol fuel, so she's paying $2.359 per gallon.

12344mag made a good point on the BTU's, and ihookem may not be clear that a tested octane is a blended octane. You don't blend up Premium and then add the alcohol for a higher octane. The blend Target is to hit all the specs that matter, while not giving valuable specs away for nothing. It's all about the money. I had huge tanks of various blendstocks and more on the way in tanker ships, and I could buy what I still might be missing. Let's say your latest test blend hit the octane spec and the RVP (Reid vapor pressure), but was shy on the midpoint. I'd have to shop around in my tanks to see what I had to raise the midpoint but not disturb the RVP and not give away octane. Octane is money. Computers really came in handy for optimizing blends.

Regarding BTU, I don't remember ever testing a blend for BTU content, which is why I said I suspected that the oxygenated gasoline was light on BTU's. But, an oxygenated gasoline blend could easily be low on midpoint, which would indicate low BTU content, but I would have had to correct that in order to meet spec. To correct it, I'd likely have to pull some of the stock (in a computer simulation) and replace it with some other stock to raise the midpoint enough to meet spec. And if I did that, I'd be raising BTU content.

That's why I said that I suspect the oxygenated gas would possibly be light on BTU's, but I don't know that for sure. All I do know is that oxygenated gasoline gives worse mileage in my vehicles, so I'm thinking that it has to be a function of BTU content.

Gasoline blending was a combination of science and the black arts. Most specs didn't blend in a linear fashion, so no matter how many simulations you ran, it was still often a guess that would have to be marginally corrected before shipping.

In a gallon of E10 gasoline you have a 10% Ethanol content. to make this you remove 12.8 Fl ounces of gasoline out of the gallon and you replace it with 12.8 Fl ounces of Ethanol, I'm sure the blending process is much more complicated than just adding or subtracting but I'm trying to make this simple.

With Gasoline at 114,500 btu and Ethanol at 76,100 btu you have less power in the gallon of E10 than you do in the gallon of E0.

ANY engine burning E10 will be less efficient than an engine burning E0.

As to the op's original question with out knowing the computer tuning of the Lexus it would be impossible to tell whether the lower octane gas would be bad for it or not.

I have a friend who has a LS3 engine in his sand buggy, he is putting 1200 hp to the wheels this is a very high performance engine and has to have the computer tuned to what ever is in the tank. If it is tuned for e10 and he uses pure gasoline he'll toast it in a very short period of time.

Performance and mileage?

Energy quotient.