prankster

iTrader: (3)

IMO, people with "six-figure job" are not the kind of people that do something without any research. Engine knocking is not an urban myth, it is real. It is a part of engine design parameters.

I think you used that as a get-away excuse when you knew that you had done something stupid.

Again like other fellow CL members have stated, if you have six-figure job, $5 saving is nothing compared to potential engine repair.

Just my 2 cents

neomedic

iTrader: (5)

Agree...why so much emotion? If OP understands the risk and want to experiment...go right ahead and report back to us. Someone has to take risks in experiments. Won't know till someone try it.

Toymota

Actually I don't mind the responses. I knew I was going to get flamed for posting something controversial like this. In some responses, you might even think I had wronged someone's mother, lol! Anyway, I did try to put up some real numbers, and I would still like to hear anyone else's real evidence that 89 or 87 octane reduces your mileage or damages your engine.

Kurtz

iTrader: (1)

What generally happens in a modern car when you run lower than required octane:


The knock sensors will detect the first hint of ping/knock and retard engine timing.

This reduces power,and also usually hurts mileage as you're getting less than optimal combustion


But the ECU knows the car is SUPPOSED to be getting the proper octane, so eventually it begins to add timing back... then it detects more ping, and retards timing again.

Over and over and over again, forever, or until you put the correct gas in the car.


So unlike the old days where it'd just ping/knock away till your engine blew up, it protects the motor.

You end up with less power, in general less mileage (this will depend on a LOT of factors though), and you ARE putting more wear on the engine, but a lot less than in the old days before advanced knock sensors.


So you probably could go 100k miles on 87 octane without needing a new engine, but if someone tore it down it'd probably look like it had 200k on it.


Anyway, a true MPG test would require the following to produce really valid data:


The same route driven, with the same frequency, on the same days and times to normalize traffic variance, using the same fuel (same brand AND same blend, meaning you can't go changing seasons), oh, and using the same tires, with the exact same inflation schedule too... (and probably a few other factors to correct for I'm not thinking of) over a reasonably long period of time... then the same done with the other octane.


A couple months, especially changing seasons, isn't nearly enough data to conclude anything.useful. By all means if the OP wants to keep collecting data long enough to make a good comparison, and he's normalizing for all the items I mention, he's welcome to do so and I'm certainly not gonna flame him for doing it.

But as noted, if Lexus could sell the car using 87 they'd love to do so. (In fact I think the ES recently did that, though it runs lower compression and makes less power than say the IS350 motor) so I think it's likely they put 91 on there for a reason with the 2IS.

udithadj

I have a 07 Rav4 V6 Sport. even though toyota recomends 87 i have seen a difference in gas milage and responsiveness onf the engine with 93. Funny thing is that lexus recommends 93 for 2GR FE engine (ES350, RX350)

Kurtz

iTrader: (1)

You can't really go by that, since the engine often has different compression, timing, programming, etc in each vehicle.

The ES350 by the way, as I just mentioned does not recommend 93.

It never did (it was 91 before), but even that was changed to 87 for the 2011 model year.

How? They changed the timing/programming. The car lost a few hp in official ratings, but was able to safely run the lower octane fuel as a result.


And FWIW, unless there's something wrong with the car, it'll never see any improvement from running a higher octane than the engine is designed/programmed to use.

the only thing octane is a measure of is resistance to knock.

That's all octane means.

So if a car is designed and programmed to not knock on 87, it won't ever run better on anything higher. It can't.

Now, if one of many possible causes is leading to knocking on that 87, you'd certainly see improvement with 93 by avoiding it... but in that case I'd suggest fixing what's wrong with the car rather than using the band aid of higher octane.


The general rule is to always use the lowest octane possible that does not, ever, knock or ping. As designed by the engineers and programmers from the factory, that is 91 for the ISx50.

Running lower is a potentially bad idea for the several reasons already discussed in the thread, though not a "your engine will explode" bad idea like it used to be year ago.

Running higher is a waste of $ in a properly running engine.

TooFly4Ya

Couldn't have said it better Kurtz, and OP your car not ours no one on here has the right to tell you what to do with "Your Car". We have done tests on a few of our cars at the shop here in Orlando and octane does make a difference on the engine. You wouldnt usually notice it right away but that TOTALLY <---- depends on the engine. Ive seen some knock in less than 5 minutes. Others knock in days. For my lex, only premium is going in nothing else, not even 95 oct like a few of the guys here use. Just my preference. Even though I would love to save $5 a fill-up.

Toymota

Hey thanks for all the replies. They have been very useful.

I am aware of the risks I am taking. The way I look at it is there would be a safety margin designed into the engine so that it does not come anywhere near knocking at any point in its operating range on 91 octane. There is also the knock sensor system as detailed by Kurtz. By stepping down to 89 mid-grade, I know that I have reduced this safety margin, and could even cause knocking under certain conditions within the usual operating range. This is why I make a point to avoid those conditions (low rpm, high load). I'm pretty sure I can make the engine knock by flooring it from a standstill with a hot engine, but not even I am stupid enough to do that. Like I mentioned, I have a very relaxed driving style, so I don't come anywhere near the design limits of the car, which makes it possible for me to conduct this experiment. If you do take your car to the design limits, then definitely do not use anything less than 91 octane!

ibidu1

iTrader: (1)

For a low hp (is250) easy commuting driver 87 octane is fine.

For a higher hp (ie IS350,ISF) 89-up octane.

You are not going to blow up your engine! You are not going to ad more wear. These cars ecu are a lot more advanced nowadays. ECU stores driving habits! If you run 87 stay at 87. If you switch octanes your cars ecu will relearn itself

350250

i only use +94 i get 495 km a tank the higher octane better gas mileage so you think you saving with cheaper gas your not probably wont harm the engine but engine wont have maximum power and car runs horrible

350250

i only use +94 i get 495 km a tank the higher octane better gas mileage so you think you saving with cheaper gas your not probably wont harm the engine but engine wont have maximum power and car runs horrible

Kurtz

iTrader: (1)

The ECU has no idea what octane your fuel is.

The only thing the ECU knows is the engine just knocked (damage to engine- though only a very very tiny amount since the sensors pick it up immediately and react)

Then the ECU retards the engine timing a bunch (pulling power and leading to less efficient combustion)

So now the knock has stopped, but you're not running as well.

After a while, because it has no idea why the engine knocked... it will slowly add timing back in.

Then it'll eventually knock again. At which point it pulls timing again.

Over and over. Forever.

Because, again, your car doesn't know a thing about what fuel you're running.

Nobody ever said you'd blow the engine.

But you will be putting a bit more wear on it than if you ran the correct fuel, in both the 250 and 350. And you'll be burning your fuel less efficiently and with less peak power available when it's pulling timing.



What's especially funny in these threads is you see them come up when gas gets more expensive... but premium is actually less of an additional cost when prices go up.... and running regular makes even less sense.

Here's the math:

Generally (round here anyway, and most places I've been) 87->89 is 10 cents more, 89->91/92/93/94 is another 10 cents.

At $1 a gallon (anyone remember that? ) for regular, you'd paid $1.20 for premium. A 20% cost bump for premium.

At a 20% price jump it might even be "worth" running regular if you want to really nickle-and-dime everything because the hit to power and economy is almost certainly less than 20%, and most people aren't keeping their car 200k miles to care about slightly more engine wear anyway.


At $4 a gallon for regular you paid $4.20 for premium. A mere 5% cost bump. And the hit to power and economy probably is probably >5%.

rookieIS

iTrader: (8)

Guys, forget about the science, costs and all those explanations regarding 89, 91, 93 etc..

Its just simple "following the instructions" when deciding what gas to fill. If the car says use premium only, then use premium! Simple as that. Lexus/Toyota/Auto engineers have made our lives easier by doing tons of R&D and come out with an answer for us, why be ignorant? They are not benefiting from what octane you use, its your car ultimately.

/rant

Qbenjamin

I don't know what's going on with my car, but I am only getting 25 mpg max on the highway. My city driving stays around 21 mpg, as my driving is almost 100% this type style.

I usually don't get above 75 mph on the highway, but I have noticed that some of you guys are getting near 32 mpg? I haven't been able to find anything else to warrant a trip to the dealer, but the highway mpg is a bit disappointing.

Oh, and btw, I only use Premium fuel in my car.

laobo979

iTrader: (5)

It's just an average of 32mpg it's not really getting 32mpg. Cause if your doing the math 32x15gallon cause of 2gallon left in the reserve equal 480 miles. I'm yet to see any post that on here miles too empty actual photo. So go by your actual mileage not average.