PSA: Lexus ES350 Use Regular Gasoline Instead
 

I just discovered that the Lexus ES350 has the exact same engine as the Camry and Avalon and that the Camry has a 1mpg combined advantage over the ES350. The only difference between these two vehicles is that the ES350 calls for the usage of premium gasoline while the Camry calls for regular. There is a very slight performance decrease in using the Regular gasoline with the ES350 compared to using Premium gasoline as mentioned on the fuel door.

According to the New EPA mpg numbers from 2007-2010 MY.
V6 Camry:19/28/ [23 combined]
ES350: 19/27/ [22 combined]

To give you an idea of how small of a performance difference:
The ES350 with Premium is rated at 272hp at 6200rpm 254 lb-ft of torque at 4700rpm while the Camry with Regular is rated at 268hp @ 6200rpm with 248 lb-ft of torque at 4700rpm. They both have a compression ratio of 10.8:1.

Another example of this occurring is with the Toyota FJ Cruiser and Toyota Tundra with the 4L V6. It is another example of a Toyota Vehicle that claims it needs Premium but actually does just fine on Regular.
Straight from the Wiki:"The 1GR-FE is the 4.0 L version. Bore is 94 mm and stroke is 95 mm. Output is 236 hp (176 kW) at 5200 rpm with 266 lb?ft (361 N?m) of torque at 4000 rpm on 87 octane, and 239 hp (178 kW) at 5200 rpm with 278 lb?ft (377 N?m) at 3700 rpm on 91 octane."


So at the very least, going with regular gasoline with save you money both on fuel and should provide a slight increase in fuel economy. For those who are concerned that the Camry weighs less and therefore gets better fuel economy... The ES350 weighs 3580lbs while the Camry V6 XLE weighs 3516lbs

Are you sure they're tuned the same?

The idea is probably good, though; I suspect that most modern cars use less gas money on regular than premium even if they're designed for premium.

Seems to me that the mileage might drop slightly using regular. If the engine is running more spark advance, which it would using premium, it should get a little more power, and a little better fuel economy. The difference in miles per dollar spent on fuel might point toward using regular, if the loss of FE was only very minor.

That's the thing though, this is a case where I specifically can show a mileage improvement going with Regular vs. Premium.

My 2 volvos both call for 91 octane but do just fine on 87. There is a very slight FE advantage for 87 octane but the 91 produces more peak power. You'll never notice it unless you're flooring it. Octane requirement is dependent on a lot of factors like air temp, coolant temp and load. Most modern engine magement systems can adapt to low octane fuel without any FE penalty.

Yeah, its true that the two cars could have different timing tables in the computers. There might also be subtle differences in camshaft design or something else which isn't published.

However, I'd love for any premium car manufacturer to have a simple switch (performance / F E ) to switch between two timing tables, with the latter requiring high-octane fuel. I bet most people would use FE mode and use the low octane.

And since I'm on my soapbox, I think any car equipped with a gauge package should include a gauge that shows the amount of knock retard.

-BC

Plenty of cars have switches for economy vs. normal vs. power, which usually change transmission programming. People in general don't use them, are usually scared witless of the switch, freak out if they accidentally hit it, and resent the economy option.

A switching timing table is really not necessary. The knock sensors on these engines function in closed feedback loop to advance timing beyond what the timing table sets until its running on the verge of knock all the time. You and I can't hear it but the knock sensor sure can. The closed loop system can be extremely aggressive and adapt to fuel octane on the fly. BMW and a few other manufactueres have started measuring the resistance between the spark plug electrodes in real time to measure the peak pressure and timing inside the cylinder. It then adjusts timing and fuel mixture for each cylinder individually for maximum performance and fuel economy.

You are correct tjts, a modern engine with a knocksensor automatically adapts to the octane rate and delivers always full power when flooring it.
On half load, it will always be as economical as possible. In my understanding, it's because of the knock sensor there IS a difference in performance. There's no difference possible without knocksensor.
Without knocksensor the 'mapping' is always adapted to the minimum octane requirement, and riding on a higher octane rate does not help you safe fuel or deliver more power.
Changing to a higher octane rate without knocksensor can help in situations where there's a lot of carbon in the cylinderhead, tuned engines (higher endcompression), changed ignition timing...

Just thought I would throw some real world data into the mix here.

Through dynamometer testing at work we were able to determine that using regular fuel in an Acura 3.5L that requires premium will increase fuel economy but will lower performance.

I'm not familiar with Acura. But I suppose there's a knocksensor on it?
About differences in FE: the energy content of a fuel can be different, independant of the octane rate. Very hard to compare. Theoretically you should investigate in a lab what's the energy content of the different fuels you're using on the runs.

Yep knock sensor. Knock events start happening like crazy under heavy load and ignition timing gets pulled way back.

Under normal driving or cruise it didn't knock at all.

Usually when manufacturers use the same engine across cars, the only difference in mileage comes in with the overall weight of the vehicle.

That 1mpg difference is likely due to the weight and maybe some aerodynamic differences.

The good news is that, with newer (at least 2004) vehicles the new O2 sensors and ethanol requirements will allow you to drive lower octane. The trick is to drive conservatively for the first few tanks. The onboard computer is going to adjust the fuel injector timing during this time as "knocks" and emissions change due to the lower octane.

Of course, you should not go back to higher octane without first repeating the same process.

Good luck and post some mileage logs ok?

Ethanol has a higher octane than gasoline.
Thats not true with cars built in the last 10 years. Modern engine management systems adapt in real time. Long term fuel trim is no longer an issue.

A knock sensor requires knock to work. That kind of knock might not blow your engine up on the first day, but inadequate octane (causing knock) over a hundred thousand miles or more will cause head gasket problems, smushed crank bearings, etc. My point is that every engine should be designed to avoid knock in the first place, not to use knock as a tuning parameter.

If there are alternate ways to avoid knock (not just react to it), that's fine too. That BMW system sounds pretty slick.

-BC

Hi Bob,
I can't agree with your vision.
It's different: an engine should be designed to not have knock with the lowest required octane rate.
A knock sensor helps you getting the benefit of higher octane rate (e.g. my Civic min. requirement is 95RON, but I can put 98 also in it). This benefit can be lower fuel consumption or higher power.
On top of it: the knock sensor protects your engine for unexpected problems (carbon, very bad fuel, a bit diesel residue, too high temperature...etc) that can cause knock.
The knock captured by the knock sensor is not dangerous at all as it's already captured from the very first signs of knock and doesn't continue for long seconds.

I'm not saying there should not be knock sensors - I agree that there could be problems (fuel issues, carbon buildup, etc.) but for this the knock sensor functions as a safety device. I don't think that the OEMs should program too much timing into their motors and just hope for the knock sensor to find the best timing, like is how I believe things are now.

I just saw a Civic in the shop last weekend that had a head gasket problem with less than 100k miles on the motor. In fact I see lots of head gasket problems (i.e. the yellowish goo under the oil cap) on 100k mile cars, on cars that are otherwise in good condition. In my opinion there are way too many head gasket failures, and I attribute this to incorrect timing from the OEMs. Not to mention that I also hear knock when I drive cars, even though the "correct" octane fuel is being used.

And a few seconds of light knock won't hurt anything, but years of knock will. I say this because I see it too often.

I'm not exactly sure what you don't agree with - do you think it's a bad idea to have an economy (low octane) / performance (high octane) switch for the driver?

- BC

Well Bob, I don't agree when you say knock shouldn't be used as a tuning parameter. It's a wonderfull parameter to adjust your timing to the limit.
It's not fair to relate headgasketproblems to existance of a knocksensor. The very limited 'allowed' knock (before ignition is retired) by the engine ECU can never cause such problems.
The way people drive is far more destructive for the headgasket (high load with cold engine), just as a broken cooling system.
An economy/performance switch for the driver seems very inconvenient to me for 2 reasons:
1)Independant of the octane rate I may need power in some situations. Those situations can be overtaking a car, crossing a street... Dangerous and I don't want to depent on a switch.
2)Economy: I want to have my engine always as efficient as possible, no matter what octane rate, when I don't need power.
All this is done automatically by the knocksensor.

Bob, which brands do you observe more of that with, and which brands do you see less?

I'm going to guess that brands with 100,000 mile warranties have safer timing...they have something to lose by making their vehicles die early.

It's fine for an OEM to use knock (although a 5-gas analyzer is much more indicative of what's going on in the cylinder) to develop an initial tune. But once they've established an optimum timing table (which should not knock except under unusual conditions), then they can use that table in the production vehicles. They put thousands of man-hours into tuning these engines, and by the time the engines reach the consumer I consider any knock to be unacceptable (provided the consumer is using the required octane level).

By the same token, I also would like to see OEMs add some retard during transitional events (i.e. throttle movement, shifting, etc.). Maybe some or all of them do this now, but the programs I've been in don't consider those events for timing.

As far as what vehicles- recently I recall seeing a Northstar, a civic (the guy just bought it for a "bargain" unfortunately), a Volvo, and a Trailblazer with foamy oil caps. But since I only work at the shop one day each week, I probably only see about 7 - 10 cars each week, and I don't really keep a log of what vehicles have problems and which ones don't.

Headgasket technology and machining practices are so far advanced nowadays that cars nowadays should all last 200K+ miles without a major failure.

-BC

I wonder if aggressive timing is part of the reason early Northstars all had premature deaths.

It's possible - I don't know much about the Northstars actually, but I did drive them as rental cars a couple of times when traveling on business. The thing is that those rental cars knocked like a bastard, even when driving pretty tame. I'm sure that when the cars were returned to the rental agency, as long as the needle pointed to "F" the companies didn't check the octane of the fuel in the tank. Most (all?) renters would just put in the cheapest crap they could to get the needle to F, instead of putting in the high-octane fuel they required...

-BC

=> only foamy oil caps or a broken headgasket? My wife's car has >80% of the time a foamy oil cap. We baught the car brand new and I also know that a foamy oil cap CAN be a sign of broken gasket. Turns out it's condensewater as she uses the car to drive only a few miles/drivecycle. In the beginning I was worried, but there's nothing going on. If I drive the car in summer to work a few times it's all gone. It's also because the valvecover and cap are of plastic and the cap is 10cm above the valve cover. With the 0W30 in it since a few weeks the mayonaise is now much thinner.
=> what you're saying it's true, but it's the financial department that decides on the cost and quality of every part.:mad:

...and the marketing department. At least the financial department cares about potential warranty, recall, and (if enough have short service life) class action lawsuit issues. The marketing department, IF they have a long view at all, cares about reputation but reputations are set in stone these days.

The poor engineering department doesn't get the involvement that they should.

Detonation and pre-ignition is what kills head gaskets, a little knock shouldn't harm anything. Have you ever taken off at a light next to a 90s ford? You'd think it was going to knock itself to death but that's just how they are. They get great economy and the bodies fall apart or the transmission dies way before the engine shows signs of fatigue.